diff --git a/src/cmd/services/m3comparator/main/parser/series_iterator_builder.go b/src/cmd/services/m3comparator/main/parser/series_iterator_builder.go
index c38252f465..6bfaec2736 100644
--- a/src/cmd/services/m3comparator/main/parser/series_iterator_builder.go
+++ b/src/cmd/services/m3comparator/main/parser/series_iterator_builder.go
@@ -21,12 +21,10 @@
 package parser
 
 import (
-	"io"
 	"time"
 
 	"github.com/m3db/m3/src/dbnode/encoding"
 	"github.com/m3db/m3/src/dbnode/encoding/m3tsz"
-	"github.com/m3db/m3/src/dbnode/namespace"
 	"github.com/m3db/m3/src/dbnode/ts"
 	"github.com/m3db/m3/src/dbnode/x/xio"
 	"github.com/m3db/m3/src/query/models"
@@ -34,9 +32,6 @@ import (
 	xtime "github.com/m3db/m3/src/x/time"
 )
 
-const sep rune = '!'
-const tagSep rune = '.'
-
 // Data is a set of datapoints.
 type Data []ts.Datapoint
 
@@ -46,9 +41,7 @@ type IngestSeries struct {
 	Tags       Tags
 }
 
-var iterAlloc = func(r io.Reader, _ namespace.SchemaDescr) encoding.ReaderIterator {
-	return m3tsz.NewReaderIterator(r, m3tsz.DefaultIntOptimizationEnabled, encoding.NewOptions())
-}
+var iterAlloc = m3tsz.DefaultReaderIteratorAllocFn(encoding.NewOptions())
 
 func buildBlockReader(
 	block Data,
diff --git a/src/cmd/tools/read_data_files/main/main.go b/src/cmd/tools/read_data_files/main/main.go
index 550d4ff563..72dfa54de2 100644
--- a/src/cmd/tools/read_data_files/main/main.go
+++ b/src/cmd/tools/read_data_files/main/main.go
@@ -21,7 +21,6 @@
 package main
 
 import (
-	"bytes"
 	"encoding/base64"
 	"fmt"
 	"io"
@@ -35,6 +34,7 @@ import (
 	"github.com/m3db/m3/src/dbnode/encoding/m3tsz"
 	"github.com/m3db/m3/src/dbnode/persist"
 	"github.com/m3db/m3/src/dbnode/persist/fs"
+	"github.com/m3db/m3/src/dbnode/x/xio"
 	"github.com/m3db/m3/src/x/ident"
 
 	"github.com/pborman/getopt"
@@ -159,7 +159,7 @@ func main() {
 		if benchMode != benchmarkSeries {
 			data.IncRef()
 
-			iter := m3tsz.NewReaderIterator(bytes.NewReader(data.Bytes()), true, encodingOpts)
+			iter := m3tsz.NewReaderIterator(xio.NewBytesReader64(data.Bytes()), true, encodingOpts)
 			for iter.Next() {
 				dp, _, annotation := iter.Current()
 				if benchMode == benchmarkNone {
diff --git a/src/dbnode/client/config.go b/src/dbnode/client/config.go
index 474346f2f6..18bc61e361 100644
--- a/src/dbnode/client/config.go
+++ b/src/dbnode/client/config.go
@@ -23,7 +23,6 @@ package client
 import (
 	"errors"
 	"fmt"
-	"io"
 	"time"
 
 	"github.com/m3db/m3/src/dbnode/encoding"
@@ -43,11 +42,6 @@ const (
 	asyncWriteWorkerPoolDefaultSize = 128
 )
 
-var (
-	errConfigurationMustSupplyConfig = errors.New(
-		"must supply config when no topology initializer parameter supplied")
-)
-
 // Configuration is a configuration that can be used to construct a client.
 type Configuration struct {
 	// The environment (static or dynamic) configuration.
@@ -412,10 +406,7 @@ func (c Configuration) NewAdminClient(
 		encodingOpts = encoding.NewOptions()
 	}
 
-	v = v.SetReaderIteratorAllocate(func(r io.Reader, _ namespace.SchemaDescr) encoding.ReaderIterator {
-		intOptimized := m3tsz.DefaultIntOptimizationEnabled
-		return m3tsz.NewReaderIterator(r, intOptimized, encodingOpts)
-	})
+	v = v.SetReaderIteratorAllocate(m3tsz.DefaultReaderIteratorAllocFn(encodingOpts))
 
 	if c.Proto != nil && c.Proto.Enabled {
 		v = v.SetEncodingProto(encodingOpts)
diff --git a/src/dbnode/client/fetch_tagged_results_accumulator_misc_test.go b/src/dbnode/client/fetch_tagged_results_accumulator_misc_test.go
index 2eb8d6837b..66b6e14019 100644
--- a/src/dbnode/client/fetch_tagged_results_accumulator_misc_test.go
+++ b/src/dbnode/client/fetch_tagged_results_accumulator_misc_test.go
@@ -22,7 +22,6 @@ package client
 
 import (
 	"fmt"
-	"io"
 	"math/rand"
 	"os"
 	"sort"
@@ -32,7 +31,6 @@ import (
 	"github.com/m3db/m3/src/dbnode/encoding"
 	"github.com/m3db/m3/src/dbnode/encoding/m3tsz"
 	"github.com/m3db/m3/src/dbnode/generated/thrift/rpc"
-	"github.com/m3db/m3/src/dbnode/namespace"
 	"github.com/m3db/m3/src/dbnode/storage/index"
 	"github.com/m3db/m3/src/dbnode/x/xpool"
 	"github.com/m3db/m3/src/x/ident"
@@ -272,9 +270,7 @@ func initTestFetchTaggedPools() *testFetchTaggedPools {
 	pools.readerSlices.Init()
 
 	pools.multiReader = encoding.NewMultiReaderIteratorPool(opts)
-	pools.multiReader.Init(func(r io.Reader, _ namespace.SchemaDescr) encoding.ReaderIterator {
-		return m3tsz.NewReaderIterator(r, m3tsz.DefaultIntOptimizationEnabled, encoding.NewOptions())
-	})
+	pools.multiReader.Init(m3tsz.DefaultReaderIteratorAllocFn(encoding.NewOptions()))
 
 	pools.seriesIter = encoding.NewSeriesIteratorPool(opts)
 	pools.seriesIter.Init()
diff --git a/src/dbnode/client/options.go b/src/dbnode/client/options.go
index e329d0ffce..e2e3608e28 100644
--- a/src/dbnode/client/options.go
+++ b/src/dbnode/client/options.go
@@ -22,7 +22,6 @@ package client
 
 import (
 	"errors"
-	"io"
 	"math"
 	"runtime"
 	"time"
@@ -37,6 +36,7 @@ import (
 	m3dbruntime "github.com/m3db/m3/src/dbnode/runtime"
 	"github.com/m3db/m3/src/dbnode/storage/index"
 	"github.com/m3db/m3/src/dbnode/topology"
+	"github.com/m3db/m3/src/dbnode/x/xio"
 	"github.com/m3db/m3/src/x/clock"
 	"github.com/m3db/m3/src/x/context"
 	"github.com/m3db/m3/src/x/ident"
@@ -473,16 +473,17 @@ func (o *options) Validate() error {
 
 func (o *options) SetEncodingM3TSZ() Options {
 	opts := *o
-	opts.readerIteratorAllocate = func(r io.Reader, _ namespace.SchemaDescr) encoding.ReaderIterator {
-		return m3tsz.NewReaderIterator(r, m3tsz.DefaultIntOptimizationEnabled, encoding.NewOptions())
-	}
+	opts.readerIteratorAllocate = m3tsz.DefaultReaderIteratorAllocFn(encoding.NewOptions())
 	opts.isProtoEnabled = false
 	return &opts
 }
 
 func (o *options) SetEncodingProto(encodingOpts encoding.Options) Options {
 	opts := *o
-	opts.readerIteratorAllocate = func(r io.Reader, descr namespace.SchemaDescr) encoding.ReaderIterator {
+	opts.readerIteratorAllocate = func(
+		r xio.Reader64,
+		descr namespace.SchemaDescr,
+	) encoding.ReaderIterator {
 		return proto.NewIterator(r, descr, encodingOpts)
 	}
 	opts.isProtoEnabled = true
diff --git a/src/dbnode/client/session_fetch_bulk_blocks_test.go b/src/dbnode/client/session_fetch_bulk_blocks_test.go
index 611c85c97f..dac836d680 100644
--- a/src/dbnode/client/session_fetch_bulk_blocks_test.go
+++ b/src/dbnode/client/session_fetch_bulk_blocks_test.go
@@ -24,7 +24,6 @@ import (
 	"bytes"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"math"
 	"sort"
 	"sync"
@@ -58,17 +57,19 @@ import (
 )
 
 var (
-	blockSize       = 2 * time.Hour
-	nsID            = ident.StringID("testNs1")
-	nsRetentionOpts = retention.NewOptions().
-			SetBlockSize(blockSize).
-			SetRetentionPeriod(48 * blockSize)
+	blockSize = 2 * time.Hour
+	nsID      = ident.StringID("testNs1")
+
+	nsRetentionOpts = retention.NewOptions().SetBlockSize(blockSize).SetRetentionPeriod(48 * blockSize)
+
 	testTagDecodingPool = serialize.NewTagDecoderPool(
 		serialize.NewTagDecoderOptions(serialize.TagDecoderOptionsConfig{}),
 		pool.NewObjectPoolOptions().SetSize(1))
+
 	testTagEncodingPool = serialize.NewTagEncoderPool(
 		serialize.NewTagEncoderOptions(),
 		pool.NewObjectPoolOptions().SetSize(1))
+
 	testIDPool     = newSessionTestOptions().IdentifierPool()
 	fooID          = ident.StringID("foo")
 	fooTags        checked.Bytes
@@ -101,9 +102,7 @@ func testsNsMetadata(t *testing.T) namespace.Metadata {
 
 func newSessionTestMultiReaderIteratorPool() encoding.MultiReaderIteratorPool {
 	p := encoding.NewMultiReaderIteratorPool(nil)
-	p.Init(func(r io.Reader, _ namespace.SchemaDescr) encoding.ReaderIterator {
-		return m3tsz.NewReaderIterator(r, m3tsz.DefaultIntOptimizationEnabled, encoding.NewOptions())
-	})
+	p.Init(m3tsz.DefaultReaderIteratorAllocFn(encoding.NewOptions()))
 	return p
 }
 
@@ -1455,10 +1454,9 @@ func TestStreamBlocksBatchFromPeerVerifiesBlockErr(t *testing.T) {
 	require.True(t, ok)
 	segment, err := reader.Segment()
 	require.NoError(t, err)
-	rawBlockData := make([]byte, segment.Len())
-	n, err := reader.Read(rawBlockData)
-	require.NoError(t, err)
-	require.Equal(t, len(rawBlockData), n)
+	rawBlockData, err := xio.ToBytes(reader)
+	require.Equal(t, io.EOF, err)
+	require.Equal(t, len(rawBlockData), segment.Len())
 	rawBlockLen := int64(len(rawBlockData))
 
 	var (
@@ -1510,8 +1508,8 @@ func TestStreamBlocksBatchFromPeerVerifiesBlockErr(t *testing.T) {
 		Return(&rpc.FetchBlocksRawResult_{
 			Elements: []*rpc.Blocks{
 				// First foo block intact
-				&rpc.Blocks{ID: []byte("foo"), Blocks: []*rpc.Block{
-					&rpc.Block{Start: start.UnixNano(), Segments: &rpc.Segments{
+				{ID: []byte("foo"), Blocks: []*rpc.Block{
+					{Start: start.UnixNano(), Segments: &rpc.Segments{
 						Merged: &rpc.Segment{
 							Head: rawBlockData[:len(rawBlockData)-1],
 							Tail: []byte{rawBlockData[len(rawBlockData)-1]},
@@ -1519,16 +1517,16 @@ func TestStreamBlocksBatchFromPeerVerifiesBlockErr(t *testing.T) {
 					}},
 				}},
 				// First bar block intact, second with error
-				&rpc.Blocks{ID: []byte("bar"), Blocks: []*rpc.Block{
-					&rpc.Block{Start: start.UnixNano(), Segments: &rpc.Segments{
+				{ID: []byte("bar"), Blocks: []*rpc.Block{
+					{Start: start.UnixNano(), Segments: &rpc.Segments{
 						Merged: &rpc.Segment{
 							Head: rawBlockData[:len(rawBlockData)-1],
 							Tail: []byte{rawBlockData[len(rawBlockData)-1]},
 						},
 					}},
 				}},
-				&rpc.Blocks{ID: []byte("bar"), Blocks: []*rpc.Block{
-					&rpc.Block{Start: start.Add(blockSize).UnixNano(), Err: &rpc.Error{
+				{ID: []byte("bar"), Blocks: []*rpc.Block{
+					{Start: start.Add(blockSize).UnixNano(), Err: &rpc.Error{
 						Type:    rpc.ErrorType_INTERNAL_ERROR,
 						Message: "an error",
 					}},
@@ -1606,10 +1604,9 @@ func TestStreamBlocksBatchFromPeerVerifiesBlockChecksum(t *testing.T) {
 	require.True(t, ok)
 	segment, err := reader.Segment()
 	require.NoError(t, err)
-	rawBlockData := make([]byte, segment.Len())
-	n, err := reader.Read(rawBlockData)
-	require.NoError(t, err)
-	require.Equal(t, len(rawBlockData), n)
+	rawBlockData, err := xio.ToBytes(reader)
+	require.Equal(t, io.EOF, err)
+	require.Equal(t, len(rawBlockData), segment.Len())
 	rawBlockLen := int64(len(rawBlockData))
 
 	var (
@@ -1666,26 +1663,26 @@ func TestStreamBlocksBatchFromPeerVerifiesBlockChecksum(t *testing.T) {
 		Return(&rpc.FetchBlocksRawResult_{
 			Elements: []*rpc.Blocks{
 				// valid foo block
-				&rpc.Blocks{ID: []byte("foo"), Blocks: []*rpc.Block{
-					&rpc.Block{Start: start.UnixNano(), Checksum: &validChecksum, Segments: &rpc.Segments{
+				{ID: []byte("foo"), Blocks: []*rpc.Block{
+					{Start: start.UnixNano(), Checksum: &validChecksum, Segments: &rpc.Segments{
 						Merged: &rpc.Segment{
 							Head: head,
 							Tail: tail,
 						},
 					}},
 				}},
-				&rpc.Blocks{ID: []byte("bar"), Blocks: []*rpc.Block{
+				{ID: []byte("bar"), Blocks: []*rpc.Block{
 					// invalid bar block
-					&rpc.Block{Start: start.UnixNano(), Checksum: &invalidChecksum, Segments: &rpc.Segments{
+					{Start: start.UnixNano(), Checksum: &invalidChecksum, Segments: &rpc.Segments{
 						Merged: &rpc.Segment{
 							Head: head,
 							Tail: tail,
 						},
 					}},
 				}},
-				&rpc.Blocks{ID: []byte("bar"), Blocks: []*rpc.Block{
+				{ID: []byte("bar"), Blocks: []*rpc.Block{
 					// valid bar block, no checksum
-					&rpc.Block{Start: start.Add(blockSize).UnixNano(), Segments: &rpc.Segments{
+					{Start: start.Add(blockSize).UnixNano(), Segments: &rpc.Segments{
 						Merged: &rpc.Segment{
 							Head: head,
 							Tail: tail,
@@ -1769,8 +1766,8 @@ func TestBlocksResultAddBlockFromPeerReadMerged(t *testing.T) {
 	require.NoError(t, err)
 
 	// Assert block has data
-	data, err := ioutil.ReadAll(xio.NewSegmentReader(seg))
-	require.NoError(t, err)
+	data, err := xio.ToBytes(xio.NewSegmentReader(seg))
+	require.Equal(t, io.EOF, err)
 	assert.Equal(t, []byte{1, 2, 3}, data)
 }
 
diff --git a/src/dbnode/encoding/encoding.go b/src/dbnode/encoding/encoding.go
index f6623124ec..0a0389b179 100644
--- a/src/dbnode/encoding/encoding.go
+++ b/src/dbnode/encoding/encoding.go
@@ -43,7 +43,7 @@ func LeadingAndTrailingZeros(v uint64) (int, int) {
 }
 
 // SignExtend sign extends the highest bit of v which has numBits (<=64).
-func SignExtend(v uint64, numBits uint) int64 {
+func SignExtend(v uint64, numBits uint8) int64 {
 	shift := 64 - numBits
 	return (int64(v) << shift) >> shift
 }
diff --git a/src/dbnode/encoding/encoding_mock.go b/src/dbnode/encoding/encoding_mock.go
index 526895fc58..201a89c74c 100644
--- a/src/dbnode/encoding/encoding_mock.go
+++ b/src/dbnode/encoding/encoding_mock.go
@@ -25,7 +25,6 @@
 package encoding
 
 import (
-	"io"
 	"reflect"
 	"time"
 
@@ -707,7 +706,7 @@ func (mr *MockReaderIteratorMockRecorder) Close() *gomock.Call {
 }
 
 // Reset mocks base method
-func (m *MockReaderIterator) Reset(reader io.Reader, schema namespace.SchemaDescr) {
+func (m *MockReaderIterator) Reset(reader xio.Reader64, schema namespace.SchemaDescr) {
 	m.ctrl.T.Helper()
 	m.ctrl.Call(m, "Reset", reader, schema)
 }
@@ -1495,7 +1494,7 @@ func (m *MockDecoder) EXPECT() *MockDecoderMockRecorder {
 }
 
 // Decode mocks base method
-func (m *MockDecoder) Decode(reader io.Reader) ReaderIterator {
+func (m *MockDecoder) Decode(reader xio.Reader64) ReaderIterator {
 	m.ctrl.T.Helper()
 	ret := m.ctrl.Call(m, "Decode", reader)
 	ret0, _ := ret[0].(ReaderIterator)
@@ -1508,130 +1507,6 @@ func (mr *MockDecoderMockRecorder) Decode(reader interface{}) *gomock.Call {
 	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "Decode", reflect.TypeOf((*MockDecoder)(nil).Decode), reader)
 }
 
-// MockIStream is a mock of IStream interface
-type MockIStream struct {
-	ctrl     *gomock.Controller
-	recorder *MockIStreamMockRecorder
-}
-
-// MockIStreamMockRecorder is the mock recorder for MockIStream
-type MockIStreamMockRecorder struct {
-	mock *MockIStream
-}
-
-// NewMockIStream creates a new mock instance
-func NewMockIStream(ctrl *gomock.Controller) *MockIStream {
-	mock := &MockIStream{ctrl: ctrl}
-	mock.recorder = &MockIStreamMockRecorder{mock}
-	return mock
-}
-
-// EXPECT returns an object that allows the caller to indicate expected use
-func (m *MockIStream) EXPECT() *MockIStreamMockRecorder {
-	return m.recorder
-}
-
-// Read mocks base method
-func (m *MockIStream) Read(arg0 []byte) (int, error) {
-	m.ctrl.T.Helper()
-	ret := m.ctrl.Call(m, "Read", arg0)
-	ret0, _ := ret[0].(int)
-	ret1, _ := ret[1].(error)
-	return ret0, ret1
-}
-
-// Read indicates an expected call of Read
-func (mr *MockIStreamMockRecorder) Read(arg0 interface{}) *gomock.Call {
-	mr.mock.ctrl.T.Helper()
-	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "Read", reflect.TypeOf((*MockIStream)(nil).Read), arg0)
-}
-
-// ReadBit mocks base method
-func (m *MockIStream) ReadBit() (Bit, error) {
-	m.ctrl.T.Helper()
-	ret := m.ctrl.Call(m, "ReadBit")
-	ret0, _ := ret[0].(Bit)
-	ret1, _ := ret[1].(error)
-	return ret0, ret1
-}
-
-// ReadBit indicates an expected call of ReadBit
-func (mr *MockIStreamMockRecorder) ReadBit() *gomock.Call {
-	mr.mock.ctrl.T.Helper()
-	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "ReadBit", reflect.TypeOf((*MockIStream)(nil).ReadBit))
-}
-
-// ReadByte mocks base method
-func (m *MockIStream) ReadByte() (byte, error) {
-	m.ctrl.T.Helper()
-	ret := m.ctrl.Call(m, "ReadByte")
-	ret0, _ := ret[0].(byte)
-	ret1, _ := ret[1].(error)
-	return ret0, ret1
-}
-
-// ReadByte indicates an expected call of ReadByte
-func (mr *MockIStreamMockRecorder) ReadByte() *gomock.Call {
-	mr.mock.ctrl.T.Helper()
-	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "ReadByte", reflect.TypeOf((*MockIStream)(nil).ReadByte))
-}
-
-// ReadBits mocks base method
-func (m *MockIStream) ReadBits(numBits uint) (uint64, error) {
-	m.ctrl.T.Helper()
-	ret := m.ctrl.Call(m, "ReadBits", numBits)
-	ret0, _ := ret[0].(uint64)
-	ret1, _ := ret[1].(error)
-	return ret0, ret1
-}
-
-// ReadBits indicates an expected call of ReadBits
-func (mr *MockIStreamMockRecorder) ReadBits(numBits interface{}) *gomock.Call {
-	mr.mock.ctrl.T.Helper()
-	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "ReadBits", reflect.TypeOf((*MockIStream)(nil).ReadBits), numBits)
-}
-
-// PeekBits mocks base method
-func (m *MockIStream) PeekBits(numBits uint) (uint64, error) {
-	m.ctrl.T.Helper()
-	ret := m.ctrl.Call(m, "PeekBits", numBits)
-	ret0, _ := ret[0].(uint64)
-	ret1, _ := ret[1].(error)
-	return ret0, ret1
-}
-
-// PeekBits indicates an expected call of PeekBits
-func (mr *MockIStreamMockRecorder) PeekBits(numBits interface{}) *gomock.Call {
-	mr.mock.ctrl.T.Helper()
-	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "PeekBits", reflect.TypeOf((*MockIStream)(nil).PeekBits), numBits)
-}
-
-// RemainingBitsInCurrentByte mocks base method
-func (m *MockIStream) RemainingBitsInCurrentByte() uint {
-	m.ctrl.T.Helper()
-	ret := m.ctrl.Call(m, "RemainingBitsInCurrentByte")
-	ret0, _ := ret[0].(uint)
-	return ret0
-}
-
-// RemainingBitsInCurrentByte indicates an expected call of RemainingBitsInCurrentByte
-func (mr *MockIStreamMockRecorder) RemainingBitsInCurrentByte() *gomock.Call {
-	mr.mock.ctrl.T.Helper()
-	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "RemainingBitsInCurrentByte", reflect.TypeOf((*MockIStream)(nil).RemainingBitsInCurrentByte))
-}
-
-// Reset mocks base method
-func (m *MockIStream) Reset(r io.Reader) {
-	m.ctrl.T.Helper()
-	m.ctrl.Call(m, "Reset", r)
-}
-
-// Reset indicates an expected call of Reset
-func (mr *MockIStreamMockRecorder) Reset(r interface{}) *gomock.Call {
-	mr.mock.ctrl.T.Helper()
-	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "Reset", reflect.TypeOf((*MockIStream)(nil).Reset), r)
-}
-
 // MockOStream is a mock of OStream interface
 type MockOStream struct {
 	ctrl     *gomock.Controller
diff --git a/src/dbnode/encoding/istream.go b/src/dbnode/encoding/istream.go
index f4eeba5426..1d1d2e6a83 100644
--- a/src/dbnode/encoding/istream.go
+++ b/src/dbnode/encoding/istream.go
@@ -21,169 +21,121 @@
 package encoding
 
 import (
-	"bufio"
 	"io"
-	"math"
-)
 
-// istream encapsulates a readable stream.
-type istream struct {
-	r         *bufio.Reader // encoded stream
-	err       error         // error encountered
-	current   byte          // current byte we are working off of
-	buffer    []byte        // buffer for reading in multiple bytes
-	remaining uint          // bits remaining in current to be read
-}
+	"github.com/m3db/m3/src/dbnode/x/xio"
+)
 
-// NewIStream creates a new Istream
-func NewIStream(reader io.Reader, bufioSize int) IStream {
-	return &istream{
-		r: bufio.NewReaderSize(reader, bufioSize),
-		// Buffer meant to hold uint64 size of bytes.
-		buffer: make([]byte, 8),
-	}
+// IStream encapsulates a readable stream.
+type IStream struct {
+	r         xio.Reader64
+	err       error  // error encountered
+	current   uint64 // current uint64 we are working off of
+	index     int    // current index within data slice
+	remaining uint8  // bits remaining in current to be read
 }
 
-func (is *istream) ReadBit() (Bit, error) {
-	if is.err != nil {
-		return 0, is.err
-	}
-	if is.remaining == 0 {
-		if err := is.readByteFromStream(); err != nil {
-			return 0, err
-		}
-	}
-	return Bit(is.consumeBuffer(1)), nil
+// NewIStream creates a new IStream
+func NewIStream(reader64 xio.Reader64) *IStream {
+	return &IStream{r: reader64}
 }
 
-func (is *istream) Read(b []byte) (int, error) {
-	if is.remaining == 0 {
-		// Optimized path for when the iterator is already aligned on a byte boundary. Avoids
-		// all the bit manipulation and ReadByte() function calls.
-		// Use ReadFull because the bufferedReader may not return the requested number of bytes.
-		return io.ReadFull(is.r, b)
-	}
-
-	var (
-		i   int
-		err error
-	)
-
+// Read reads len(b) bytes.
+func (is *IStream) Read(b []byte) (int, error) {
+	var i int
 	for ; i < len(b); i++ {
-		b[i], err = is.ReadByte()
+		res, err := is.ReadBits(8)
 		if err != nil {
 			return i, err
 		}
+		b[i] = byte(res)
 	}
 	return i, nil
 }
 
-func (is *istream) ReadByte() (byte, error) {
-	if is.err != nil {
-		return 0, is.err
-	}
-	remaining := is.remaining
-	res := is.consumeBuffer(remaining)
-	if remaining == 8 {
-		return res, nil
-	}
-	if err := is.readByteFromStream(); err != nil {
-		return 0, err
-	}
-	res = (res << uint(8-remaining)) | is.consumeBuffer(8-remaining)
-	return res, nil
+// ReadByte reads the next Byte.
+func (is *IStream) ReadByte() (byte, error) {
+	res, err := is.ReadBits(8)
+	return byte(res), err
+}
+
+// ReadBit reads the next Bit.
+func (is *IStream) ReadBit() (Bit, error) {
+	res, err := is.ReadBits(1)
+	return Bit(res), err
 }
 
-func (is *istream) ReadBits(numBits uint) (uint64, error) {
+// ReadBits reads the next Bits.
+func (is *IStream) ReadBits(numBits uint8) (uint64, error) {
 	if is.err != nil {
 		return 0, is.err
 	}
-	var res uint64
-	numBytes := numBits / 8
-	if numBytes > 0 {
-		// Use Read call rather than individual ReadByte calls since it has
-		// optimized path for when the iterator is aligned on a byte boundary.
-		bytes := is.buffer[0:numBytes]
-		_, err := is.Read(bytes)
-		if err != nil {
-			return 0, err
-		}
-		for _, b := range bytes {
-			res = (res << 8) | uint64(b)
-		}
+	if numBits <= is.remaining {
+		// Have enough bits buffered.
+		return is.consumeBuffer(numBits), nil
 	}
-
-	numBits = numBits % 8
-	for numBits > 0 {
-		// This is equivalent to calling is.ReadBit() in a loop but some manual inlining
-		// has been performed to optimize this loop as its heavily used in the hot path.
-		if is.remaining == 0 {
-			if err := is.readByteFromStream(); err != nil {
-				return 0, err
-			}
-		}
-
-		numToRead := numBits
-		if is.remaining < numToRead {
-			numToRead = is.remaining
-		}
-		bits := is.current >> (8 - numToRead)
-		is.current <<= numToRead
-		is.remaining -= numToRead
-		res = (res << uint64(numToRead)) | uint64(bits)
-		numBits -= numToRead
+	res := readBitsInWord(is.current, numBits)
+	// Not enough bits buffered, read next word from the stream.
+	bitsNeeded := numBits - is.remaining
+	if err := is.readWordFromStream(); err != nil {
+		return 0, err
+	}
+	if is.remaining < bitsNeeded {
+		return 0, io.EOF
 	}
-	return res, nil
+	return res | is.consumeBuffer(bitsNeeded), nil
 }
 
-func (is *istream) PeekBits(numBits uint) (uint64, error) {
-	// check the last byte first
+// PeekBits looks at the next Bits, but doesn't move the pos.
+func (is *IStream) PeekBits(numBits uint8) (uint64, error) {
 	if numBits <= is.remaining {
-		return uint64(readBitsInByte(is.current, numBits)), nil
+		return readBitsInWord(is.current, numBits), nil
 	}
-	// now check the bytes buffered and read more if necessary.
-	numBitsRead := is.remaining
-	res := uint64(readBitsInByte(is.current, is.remaining))
-	numBytesToRead := int(math.Ceil(float64(numBits-numBitsRead) / 8))
-	bytesRead, err := is.r.Peek(numBytesToRead)
+	res := readBitsInWord(is.current, numBits)
+	bitsNeeded := numBits - is.remaining
+	next, bytes, err := is.r.Peek64()
 	if err != nil {
 		return 0, err
 	}
-	for i := 0; i < numBytesToRead-1; i++ {
-		res = (res << 8) | uint64(bytesRead[i])
-		numBitsRead += 8
+	rem := 8 * bytes
+	if rem < bitsNeeded {
+		return 0, io.EOF
 	}
-	remainder := readBitsInByte(bytesRead[numBytesToRead-1], numBits-numBitsRead)
-	res = (res << (numBits - numBitsRead)) | uint64(remainder)
-	return res, nil
+	return res | readBitsInWord(next, bitsNeeded), nil
 }
 
-func (is *istream) RemainingBitsInCurrentByte() uint {
-	return is.remaining
+// RemainingBitsInCurrentByte returns the number of bits remaining to be read in the current byte.
+func (is *IStream) RemainingBitsInCurrentByte() uint {
+	return uint(is.remaining % 8)
 }
 
-// readBitsInByte reads numBits in byte b.
-func readBitsInByte(b byte, numBits uint) byte {
-	return b >> (8 - numBits)
+// readBitsInWord reads the first numBits in word w.
+func readBitsInWord(w uint64, numBits uint8) uint64 {
+	return w >> (64 - numBits)
 }
 
 // consumeBuffer consumes numBits in is.current.
-func (is *istream) consumeBuffer(numBits uint) byte {
-	res := readBitsInByte(is.current, numBits)
+func (is *IStream) consumeBuffer(numBits uint8) uint64 {
+	res := readBitsInWord(is.current, numBits)
 	is.current <<= numBits
 	is.remaining -= numBits
 	return res
 }
 
-func (is *istream) readByteFromStream() error {
-	is.current, is.err = is.r.ReadByte()
-	is.remaining = 8
-	return is.err
+func (is *IStream) readWordFromStream() error {
+	current, bytes, err := is.r.Read64()
+	is.current = current
+	is.remaining = 8 * bytes
+	is.err = err
+
+	return err
 }
 
-func (is *istream) Reset(r io.Reader) {
-	is.r.Reset(r)
+// Reset resets the IStream.
+func (is *IStream) Reset(reader xio.Reader64) {
 	is.err = nil
 	is.current = 0
 	is.remaining = 0
+	is.index = 0
+	is.r = reader
 }
diff --git a/src/dbnode/encoding/istream_test.go b/src/dbnode/encoding/istream_test.go
index 4841590b01..eddc4dd30d 100644
--- a/src/dbnode/encoding/istream_test.go
+++ b/src/dbnode/encoding/istream_test.go
@@ -21,21 +21,22 @@
 package encoding
 
 import (
-	"bytes"
+	"io"
 	"testing"
 
 	"github.com/stretchr/testify/require"
+
+	"github.com/m3db/m3/src/dbnode/x/xio"
 )
 
-func TestReadBits(t *testing.T) {
+func TestIStreamReadBits(t *testing.T) {
 	byteStream := []byte{
 		0xca, 0xfe, 0xfd, 0x89, 0x1a, 0x2b, 0x3c, 0x48, 0x55, 0xe6, 0xf7,
 		0x80, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x80,
 	}
 
-	o := NewIStream(bytes.NewReader(byteStream), 16)
-	is := o.(*istream)
-	numBits := []uint{1, 3, 4, 8, 7, 2, 64, 64}
+	is := NewIStream(xio.NewBytesReader64(byteStream))
+	numBits := []byte{1, 3, 4, 8, 7, 2, 64, 64}
 	var res []uint64
 	for _, v := range numBits {
 		read, err := is.ReadBits(v)
@@ -46,15 +47,35 @@ func TestReadBits(t *testing.T) {
 	require.Equal(t, expected, res)
 
 	_, err := is.ReadBits(8)
-	require.Error(t, err)
+	require.EqualError(t, err, io.EOF.Error())
 }
 
-func TestPeekBitsSuccess(t *testing.T) {
+func TestIStreamReadByte(t *testing.T) {
+	var (
+		byteStream = []uint8{
+			0xca, 0xfe, 0xfd, 0x89, 0x1a, 0x2b, 0x3c, 0x48, 0x55, 0xe6, 0xf7,
+			0x80, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x80,
+		}
+		is  = NewIStream(xio.NewBytesReader64(byteStream))
+		res = make([]byte, 0, len(byteStream))
+	)
+
+	for range byteStream {
+		read, err := is.ReadByte()
+		require.NoError(t, err)
+		res = append(res, read)
+	}
+	require.Equal(t, byteStream, res)
+
+	_, err := is.ReadByte()
+	require.EqualError(t, err, io.EOF.Error())
+}
+
+func TestIStreamPeekBitsSuccess(t *testing.T) {
 	byteStream := []byte{0xa9, 0xfe, 0xfe, 0xdf, 0x9b, 0x57, 0x21, 0xf1}
-	o := NewIStream(bytes.NewReader(byteStream), 16)
-	is := o.(*istream)
+	is := NewIStream(xio.NewBytesReader64(byteStream))
 	inputs := []struct {
-		numBits  uint
+		numBits  uint8
 		expected uint64
 	}{
 		{0, 0},
@@ -71,31 +92,29 @@ func TestPeekBitsSuccess(t *testing.T) {
 		require.NoError(t, err)
 		require.Equal(t, input.expected, res)
 	}
-	require.Equal(t, byte(0), is.current)
+	require.Equal(t, uint64(0), is.current)
 	require.Equal(t, 0, int(is.remaining))
 }
 
-func TestPeekBitsError(t *testing.T) {
+func TestIStreamPeekBitsError(t *testing.T) {
 	byteStream := []byte{0x1, 0x2}
-	o := NewIStream(bytes.NewReader(byteStream), 16)
-	is := o.(*istream)
+	is := NewIStream(xio.NewBytesReader64(byteStream))
 	res, err := is.PeekBits(20)
-	require.Error(t, err)
+	require.EqualError(t, err, io.EOF.Error())
 	require.Equal(t, uint64(0), res)
 }
 
-func TestReadAfterPeekBits(t *testing.T) {
+func TestIStreamReadAfterPeekBits(t *testing.T) {
 	byteStream := []byte{0xab, 0xcd}
-	o := NewIStream(bytes.NewReader(byteStream), 16)
-	is := o.(*istream)
+	is := NewIStream(xio.NewBytesReader64(byteStream))
 	res, err := is.PeekBits(10)
 	require.NoError(t, err)
 	require.Equal(t, uint64(0x2af), res)
 	_, err = is.PeekBits(20)
-	require.Error(t, err)
+	require.EqualError(t, err, io.EOF.Error())
 
 	inputs := []struct {
-		numBits  uint
+		numBits  uint8
 		expected uint64
 	}{
 		{2, 0x2},
@@ -107,14 +126,62 @@ func TestReadAfterPeekBits(t *testing.T) {
 		require.Equal(t, input.expected, res)
 	}
 	_, err = is.ReadBits(8)
-	require.Error(t, err)
+	require.EqualError(t, err, io.EOF.Error())
 }
 
-func TestResetIStream(t *testing.T) {
-	o := NewIStream(bytes.NewReader(nil), 16)
-	is := o.(*istream)
-	is.ReadBits(1)
-	is.Reset(bytes.NewReader(nil))
-	require.Equal(t, byte(0), is.current)
-	require.Equal(t, 0, int(is.remaining))
+func TestIStreamPeekAfterReadBits(t *testing.T) {
+	byteStream := []byte{0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8, 0x9, 0xA}
+	is := NewIStream(xio.NewBytesReader64(byteStream))
+
+	res, err := is.ReadBits(16)
+	require.NoError(t, err)
+	require.Equal(t, uint64(0x102), res)
+
+	res, err = is.PeekBits(63)
+	require.NoError(t, err)
+	require.Equal(t, uint64(0x30405060708090A)>>1, res)
+
+	res, err = is.PeekBits(64)
+	require.NoError(t, err)
+	require.Equal(t, uint64(0x30405060708090A), res)
+
+	res, err = is.ReadBits(1)
+	require.NoError(t, err)
+	require.Equal(t, uint64(0), res)
+
+	res, err = is.PeekBits(63)
+	require.NoError(t, err)
+	require.Equal(t, uint64(0x30405060708090A), res)
+
+	_, err = is.PeekBits(64)
+	require.EqualError(t, err, io.EOF.Error())
+}
+
+func TestIStreamRemainingBitsInCurrentByte(t *testing.T) {
+	byteStream := []byte{0xff, 0, 0x42}
+	is := NewIStream(xio.NewBytesReader64(byteStream))
+	for _, b := range byteStream {
+		for i := 0; i < 8; i++ {
+			var expected uint
+			if i > 0 {
+				expected = uint(8 - i)
+			}
+			require.Equal(t, expected, is.RemainingBitsInCurrentByte())
+			bit, err := is.ReadBit()
+			require.NoError(t, err)
+			expectedBit := Bit(b>>i) & 1
+			require.Equal(t, expectedBit, bit)
+		}
+	}
+}
+
+func TestIStreamReset(t *testing.T) {
+	is := NewIStream(xio.NewBytesReader64([]byte{0xff}))
+	_, _ = is.ReadBits(8)
+	_, _ = is.ReadBits(1)
+	is.Reset(xio.NewBytesReader64(nil))
+	require.Equal(t, uint64(0), is.current)
+	require.Equal(t, uint8(0), is.remaining)
+	require.Equal(t, 0, is.index)
+	require.NoError(t, is.err)
 }
diff --git a/src/dbnode/encoding/iterator_test.go b/src/dbnode/encoding/iterator_test.go
index f0a33c9357..ec6f4b065d 100644
--- a/src/dbnode/encoding/iterator_test.go
+++ b/src/dbnode/encoding/iterator_test.go
@@ -21,7 +21,6 @@
 package encoding
 
 import (
-	"io"
 	"time"
 
 	"github.com/m3db/m3/src/dbnode/namespace"
@@ -44,7 +43,7 @@ type testIterator struct {
 	closed  bool
 	err     error
 	onNext  func(oldIdx, newIdx int)
-	onReset func(r io.Reader, descr namespace.SchemaDescr)
+	onReset func(r xio.Reader64, descr namespace.SchemaDescr)
 }
 
 func newTestIterator(values []testValue) ReaderIterator {
@@ -72,7 +71,7 @@ func (it *testIterator) Current() (ts.Datapoint, xtime.Unit, ts.Annotation) {
 	}
 	v := it.values[idx]
 	dp := ts.Datapoint{Timestamp: v.t, TimestampNanos: xtime.ToUnixNano(v.t), Value: v.value}
-	return dp, v.unit, ts.Annotation(v.annotation)
+	return dp, v.unit, v.annotation
 }
 
 func (it *testIterator) Err() error {
@@ -83,7 +82,7 @@ func (it *testIterator) Close() {
 	it.closed = true
 }
 
-func (it *testIterator) Reset(r io.Reader, descr namespace.SchemaDescr) {
+func (it *testIterator) Reset(r xio.Reader64, descr namespace.SchemaDescr) {
 	it.onReset(r, descr)
 }
 
@@ -101,7 +100,7 @@ type testMultiIterator struct {
 	closed  bool
 	err     error
 	onNext  func(oldIdx, newIdx int)
-	onReset func(r io.Reader)
+	onReset func(r xio.Reader64)
 }
 
 func newTestMultiIterator(values []testValue, err error) MultiReaderIterator {
@@ -129,7 +128,7 @@ func (it *testMultiIterator) Current() (ts.Datapoint, xtime.Unit, ts.Annotation)
 	}
 	v := it.values[idx]
 	dp := ts.Datapoint{Timestamp: v.t, TimestampNanos: xtime.ToUnixNano(v.t), Value: v.value}
-	return dp, v.unit, ts.Annotation(v.annotation)
+	return dp, v.unit, v.annotation
 }
 
 func (it *testMultiIterator) Err() error {
@@ -215,10 +214,11 @@ func (it *testReaderSliceOfSlicesIterator) arrayIdx() int {
 }
 
 type testNoopReader struct {
-	n int // return for "n", also required so that each struct construction has its address
+	n byte // return for "n", also required so that each struct construction has its address
 }
 
-func (r *testNoopReader) Read(p []byte) (int, error)   { return r.n, nil }
+func (r *testNoopReader) Read64() (word uint64, n byte, err error) { return 0, r.n, nil }
+func (r *testNoopReader) Peek64() (word uint64, n byte, err error) { return 0, r.n, nil }
 func (r *testNoopReader) Segment() (ts.Segment, error) { return ts.Segment{}, nil }
 func (r *testNoopReader) Reset(ts.Segment)             {}
 func (r *testNoopReader) Finalize()                    {}
diff --git a/src/dbnode/encoding/m3tsz/decoder.go b/src/dbnode/encoding/m3tsz/decoder.go
index e29812dc31..e9d0d38e06 100644
--- a/src/dbnode/encoding/m3tsz/decoder.go
+++ b/src/dbnode/encoding/m3tsz/decoder.go
@@ -21,9 +21,8 @@
 package m3tsz
 
 import (
-	"io"
-
 	"github.com/m3db/m3/src/dbnode/encoding"
+	"github.com/m3db/m3/src/dbnode/x/xio"
 )
 
 type decoder struct {
@@ -40,6 +39,6 @@ func NewDecoder(intOptimized bool, opts encoding.Options) encoding.Decoder {
 }
 
 // Decode decodes the encoded data captured by the reader.
-func (dec *decoder) Decode(reader io.Reader) encoding.ReaderIterator {
+func (dec *decoder) Decode(reader xio.Reader64) encoding.ReaderIterator {
 	return NewReaderIterator(reader, dec.intOptimized, dec.opts)
 }
diff --git a/src/dbnode/encoding/m3tsz/decoder_benchmark_test.go b/src/dbnode/encoding/m3tsz/decoder_benchmark_test.go
new file mode 100644
index 0000000000..0f70c7b4da
--- /dev/null
+++ b/src/dbnode/encoding/m3tsz/decoder_benchmark_test.go
@@ -0,0 +1,71 @@
+// Copyright (c) 2020 Uber Technologies, Inc.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+
+package m3tsz
+
+import (
+	"encoding/base64"
+	"math/rand"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/m3db/m3/src/dbnode/encoding"
+	"github.com/m3db/m3/src/dbnode/x/xio"
+)
+
+// BenchmarkM3TSZDecode-12    	   16867	     69272 ns/op
+func BenchmarkM3TSZDecode(b *testing.B) {
+	var (
+		encodingOpts = encoding.NewOptions()
+		reader       = xio.NewBytesReader64(nil)
+		seriesRun    = prepareSampleSeriesRun(b)
+	)
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		reader.Reset(seriesRun[i])
+		iter := NewReaderIterator(reader, DefaultIntOptimizationEnabled, encodingOpts)
+		for iter.Next() {
+			_, _, _ = iter.Current()
+		}
+		require.NoError(b, iter.Err())
+	}
+}
+
+func prepareSampleSeriesRun(b *testing.B) [][]byte {
+	var (
+		rnd          = rand.New(rand.NewSource(42)) // nolint: gosec
+		sampleSeries = make([][]byte, 0, len(sampleSeriesBase64))
+		seriesRun    = make([][]byte, 0, b.N)
+	)
+
+	for _, b64 := range sampleSeriesBase64 {
+		data, err := base64.StdEncoding.DecodeString(b64)
+		require.NoError(b, err)
+		sampleSeries = append(sampleSeries, data)
+	}
+
+	for i := 0; i < b.N; i++ {
+		seriesRun = append(seriesRun, sampleSeries[rnd.Intn(len(sampleSeries))])
+	}
+
+	return seriesRun
+}
diff --git a/src/dbnode/encoding/m3tsz/encoder_benchmark_test.go b/src/dbnode/encoding/m3tsz/encoder_benchmark_test.go
index 67c62b4660..02e5cf9f68 100644
--- a/src/dbnode/encoding/m3tsz/encoder_benchmark_test.go
+++ b/src/dbnode/encoding/m3tsz/encoder_benchmark_test.go
@@ -21,7 +21,6 @@
 package m3tsz
 
 import (
-	"bytes"
 	"encoding/base64"
 	"math/rand"
 	"testing"
@@ -31,6 +30,7 @@ import (
 
 	"github.com/m3db/m3/src/dbnode/encoding"
 	"github.com/m3db/m3/src/dbnode/ts"
+	"github.com/m3db/m3/src/dbnode/x/xio"
 	xtime "github.com/m3db/m3/src/x/time"
 )
 
@@ -75,7 +75,7 @@ func prepareSampleSeriesEncRun(b *testing.B) [][]ts.Datapoint {
 		sampleSeries = make([][]byte, 0, len(sampleSeriesBase64))
 		seriesRun    = make([][]ts.Datapoint, b.N)
 		encodingOpts = encoding.NewOptions()
-		reader       = bytes.NewReader(nil)
+		reader       = xio.NewBytesReader64(nil)
 	)
 
 	for _, b64 := range sampleSeriesBase64 {
diff --git a/src/dbnode/encoding/m3tsz/encoder_test.go b/src/dbnode/encoding/m3tsz/encoder_test.go
index 13eb54e761..7b85b790b7 100644
--- a/src/dbnode/encoding/m3tsz/encoder_test.go
+++ b/src/dbnode/encoding/m3tsz/encoder_test.go
@@ -21,12 +21,14 @@
 package m3tsz
 
 import (
+	"io"
 	"math/rand"
 	"testing"
 	"time"
 
 	"github.com/m3db/m3/src/dbnode/encoding"
 	"github.com/m3db/m3/src/dbnode/ts"
+	"github.com/m3db/m3/src/dbnode/x/xio"
 	"github.com/m3db/m3/src/x/checked"
 	"github.com/m3db/m3/src/x/context"
 	xtime "github.com/m3db/m3/src/x/time"
@@ -160,10 +162,11 @@ func getBytes(t *testing.T, e encoding.Encoder) []byte {
 	if !ok {
 		return nil
 	}
-	var b [1000]byte
-	n, err := r.Read(b[:])
-	require.NoError(t, err)
-	return b[:n]
+
+	bytes, err := xio.ToBytes(r)
+	assert.Equal(t, io.EOF, err)
+
+	return bytes
 }
 
 func TestWriteTimeUnit(t *testing.T) {
diff --git a/src/dbnode/encoding/m3tsz/float_encoder_iterator.go b/src/dbnode/encoding/m3tsz/float_encoder_iterator.go
index b27f959ac2..9a4348b816 100644
--- a/src/dbnode/encoding/m3tsz/float_encoder_iterator.go
+++ b/src/dbnode/encoding/m3tsz/float_encoder_iterator.go
@@ -55,7 +55,7 @@ func (eit *FloatEncoderAndIterator) WriteFloat(stream encoding.OStream, val floa
 }
 
 // ReadFloat reads a compressed float from the stream.
-func (eit *FloatEncoderAndIterator) ReadFloat(stream encoding.IStream) error {
+func (eit *FloatEncoderAndIterator) ReadFloat(stream *encoding.IStream) error {
 	if eit.NotFirst {
 		return eit.readNextFloat(stream)
 	}
@@ -102,7 +102,7 @@ func (eit *FloatEncoderAndIterator) writeXOR(stream encoding.OStream, currXOR ui
 	stream.WriteBits(currXOR>>uint(curTrailing), numMeaningfulBits)
 }
 
-func (eit *FloatEncoderAndIterator) readFullFloat(stream encoding.IStream) error {
+func (eit *FloatEncoderAndIterator) readFullFloat(stream *encoding.IStream) error {
 	vb, err := stream.ReadBits(64)
 	if err != nil {
 		return err
@@ -114,7 +114,7 @@ func (eit *FloatEncoderAndIterator) readFullFloat(stream encoding.IStream) error
 	return nil
 }
 
-func (eit *FloatEncoderAndIterator) readNextFloat(stream encoding.IStream) error {
+func (eit *FloatEncoderAndIterator) readNextFloat(stream *encoding.IStream) error {
 	cb, err := stream.ReadBits(1)
 	if err != nil {
 		return err
@@ -122,7 +122,6 @@ func (eit *FloatEncoderAndIterator) readNextFloat(stream encoding.IStream) error
 
 	if cb == opcodeZeroValueXOR {
 		eit.PrevXOR = 0
-		eit.PrevFloatBits ^= eit.PrevXOR
 		return nil
 	}
 
@@ -134,7 +133,7 @@ func (eit *FloatEncoderAndIterator) readNextFloat(stream encoding.IStream) error
 	cb = (cb << 1) | nextCB
 	if cb == opcodeContainedValueXOR {
 		previousLeading, previousTrailing := encoding.LeadingAndTrailingZeros(eit.PrevXOR)
-		numMeaningfulBits := uint(64 - previousLeading - previousTrailing)
+		numMeaningfulBits := uint8(64 - previousLeading - previousTrailing)
 		meaningfulBits, err := stream.ReadBits(numMeaningfulBits)
 		if err != nil {
 			return err
@@ -153,7 +152,7 @@ func (eit *FloatEncoderAndIterator) readNextFloat(stream encoding.IStream) error
 	numLeadingZeros := (numLeadingZeroesAndNumMeaningfulBits & bits12To6Mask) >> 6
 	numMeaningfulBits := (numLeadingZeroesAndNumMeaningfulBits & bits6To0Mask) + 1
 
-	meaningfulBits, err := stream.ReadBits(uint(numMeaningfulBits))
+	meaningfulBits, err := stream.ReadBits(uint8(numMeaningfulBits))
 	if err != nil {
 		return err
 	}
diff --git a/src/dbnode/encoding/m3tsz/iterator.go b/src/dbnode/encoding/m3tsz/iterator.go
index b2f7e69fa2..22a1be963a 100644
--- a/src/dbnode/encoding/m3tsz/iterator.go
+++ b/src/dbnode/encoding/m3tsz/iterator.go
@@ -21,19 +21,28 @@
 package m3tsz
 
 import (
-	"io"
 	"math"
 
 	"github.com/m3db/m3/src/dbnode/encoding"
 	"github.com/m3db/m3/src/dbnode/namespace"
 	"github.com/m3db/m3/src/dbnode/ts"
+	"github.com/m3db/m3/src/dbnode/x/xio"
 	xtime "github.com/m3db/m3/src/x/time"
 )
 
+// DefaultReaderIteratorAllocFn returns a function for allocating NewReaderIterator.
+func DefaultReaderIteratorAllocFn(
+	opts encoding.Options,
+) func(r xio.Reader64, _ namespace.SchemaDescr) encoding.ReaderIterator {
+	return func(r xio.Reader64, _ namespace.SchemaDescr) encoding.ReaderIterator {
+		return NewReaderIterator(r, DefaultIntOptimizationEnabled, opts)
+	}
+}
+
 // readerIterator provides an interface for clients to incrementally
 // read datapoints off of an encoded stream.
 type readerIterator struct {
-	is   encoding.IStream
+	is   *encoding.IStream
 	opts encoding.Options
 
 	err        error   // current error
@@ -51,9 +60,13 @@ type readerIterator struct {
 }
 
 // NewReaderIterator returns a new iterator for a given reader
-func NewReaderIterator(reader io.Reader, intOptimized bool, opts encoding.Options) encoding.ReaderIterator {
+func NewReaderIterator(
+	reader xio.Reader64,
+	intOptimized bool,
+	opts encoding.Options,
+) encoding.ReaderIterator {
 	return &readerIterator{
-		is:           encoding.NewIStream(reader, opts.IStreamReaderSizeM3TSZ()),
+		is:           encoding.NewIStream(reader),
 		opts:         opts,
 		tsIterator:   NewTimestampIterator(opts, false),
 		intOptimized: intOptimized,
@@ -165,10 +178,10 @@ func (it *readerIterator) readIntValDiff() {
 		sign = 1.0
 	}
 
-	it.intVal += sign * float64(it.readBits(uint(it.sig)))
+	it.intVal += sign * float64(it.readBits(it.sig))
 }
 
-func (it *readerIterator) readBits(numBits uint) uint64 {
+func (it *readerIterator) readBits(numBits uint8) uint64 {
 	if !it.hasNext() {
 		return 0
 	}
@@ -218,7 +231,7 @@ func (it *readerIterator) hasNext() bool {
 }
 
 // Reset resets the ReadIterator for reuse.
-func (it *readerIterator) Reset(reader io.Reader, schema namespace.SchemaDescr) {
+func (it *readerIterator) Reset(reader xio.Reader64, schema namespace.SchemaDescr) {
 	it.is.Reset(reader)
 	it.tsIterator = NewTimestampIterator(it.opts, it.tsIterator.SkipMarkers)
 	it.err = nil
diff --git a/src/dbnode/encoding/m3tsz/iterator_test.go b/src/dbnode/encoding/m3tsz/iterator_test.go
index d5550e59dd..212ff1eb13 100644
--- a/src/dbnode/encoding/m3tsz/iterator_test.go
+++ b/src/dbnode/encoding/m3tsz/iterator_test.go
@@ -21,19 +21,23 @@
 package m3tsz
 
 import (
-	"bytes"
 	"testing"
 	"time"
 
 	"github.com/m3db/m3/src/dbnode/encoding"
 	"github.com/m3db/m3/src/dbnode/ts"
+	"github.com/m3db/m3/src/dbnode/x/xio"
 	xtime "github.com/m3db/m3/src/x/time"
 
 	"github.com/stretchr/testify/require"
 )
 
 func getTestReaderIterator(rawBytes []byte) *readerIterator {
-	return NewReaderIterator(bytes.NewReader(rawBytes), false, encoding.NewOptions()).(*readerIterator)
+	return NewReaderIterator(
+		xio.NewBytesReader64(rawBytes),
+		false,
+		encoding.NewOptions(),
+	).(*readerIterator)
 }
 
 func TestReaderIteratorReadNextTimestamp(t *testing.T) {
@@ -57,7 +61,7 @@ func TestReaderIteratorReadNextTimestamp(t *testing.T) {
 	}
 
 	for _, input := range inputs {
-		stream := encoding.NewIStream(bytes.NewBuffer(input.rawBytes), 16)
+		stream := encoding.NewIStream(xio.NewBytesReader64(input.rawBytes))
 		it := NewTimestampIterator(encoding.NewOptions(), false)
 
 		it.TimeUnit = input.timeUnit
@@ -68,7 +72,7 @@ func TestReaderIteratorReadNextTimestamp(t *testing.T) {
 		require.Equal(t, input.expectedTimeDelta, it.PrevTimeDelta)
 	}
 
-	stream := encoding.NewIStream(bytes.NewBuffer([]byte{0x1}), 16)
+	stream := encoding.NewIStream(xio.NewBytesReader64([]byte{0x1}))
 	it := NewTimestampIterator(encoding.NewOptions(), false)
 	err := it.readNextTimestamp(stream)
 	require.Error(t, err)
@@ -127,7 +131,7 @@ func TestReaderIteratorReadAnnotation(t *testing.T) {
 		},
 	}
 	for _, input := range inputs {
-		stream := encoding.NewIStream(bytes.NewBuffer(input.rawBytes), 16)
+		stream := encoding.NewIStream(xio.NewBytesReader64(input.rawBytes))
 		it := NewTimestampIterator(encoding.NewOptions(), false)
 
 		err := it.readAnnotation(stream)
@@ -157,7 +161,7 @@ func TestReaderIteratorReadTimeUnit(t *testing.T) {
 		},
 	}
 	for _, input := range inputs {
-		stream := encoding.NewIStream(bytes.NewBuffer(input.rawBytes), 16)
+		stream := encoding.NewIStream(xio.NewBytesReader64(input.rawBytes))
 		it := NewTimestampIterator(encoding.NewOptions(), false)
 		it.TimeUnit = input.timeUnit
 
diff --git a/src/dbnode/encoding/m3tsz/roundtrip_test.go b/src/dbnode/encoding/m3tsz/roundtrip_test.go
index 345013ac0f..dfb98a8722 100644
--- a/src/dbnode/encoding/m3tsz/roundtrip_test.go
+++ b/src/dbnode/encoding/m3tsz/roundtrip_test.go
@@ -147,7 +147,6 @@ func validateRoundTrip(t *testing.T, input []ts.Datapoint, intOpt bool) {
 	require.True(t, ok)
 
 	it := decoder.Decode(stream)
-	require.True(t, ok)
 	defer it.Close()
 
 	i := 0
diff --git a/src/dbnode/encoding/m3tsz/timestamp_iterator.go b/src/dbnode/encoding/m3tsz/timestamp_iterator.go
index ca3402607c..a9da57e72b 100644
--- a/src/dbnode/encoding/m3tsz/timestamp_iterator.go
+++ b/src/dbnode/encoding/m3tsz/timestamp_iterator.go
@@ -31,7 +31,7 @@ import (
 )
 
 // TimestampIterator encapsulates all the state required for iterating over
-// delta-of-delta compresed timestamps.
+// delta-of-delta compressed timestamps.
 type TimestampIterator struct {
 	PrevTime      xtime.UnixNano
 	PrevTimeDelta time.Duration
@@ -41,6 +41,8 @@ type TimestampIterator struct {
 
 	Opts encoding.Options
 
+	markerEncodingScheme encoding.MarkerEncodingScheme
+
 	TimeUnitChanged bool
 	Done            bool
 
@@ -49,9 +51,8 @@ type TimestampIterator struct {
 	// for situations where looking ahead is not safe.
 	SkipMarkers bool
 
-	numValueBits         uint
-	numBits              uint
-	markerEncodingScheme encoding.MarkerEncodingScheme
+	numValueBits uint8
+	numBits      uint8
 }
 
 // NewTimestampIterator creates a new TimestampIterator.
@@ -60,14 +61,14 @@ func NewTimestampIterator(opts encoding.Options, skipMarkers bool) TimestampIter
 	return TimestampIterator{
 		Opts:                 opts,
 		SkipMarkers:          skipMarkers,
-		numValueBits:         uint(mes.NumValueBits()),
-		numBits:              uint(mes.NumOpcodeBits() + mes.NumValueBits()),
+		numValueBits:         uint8(mes.NumValueBits()),
+		numBits:              uint8(mes.NumOpcodeBits() + mes.NumValueBits()),
 		markerEncodingScheme: mes,
 	}
 }
 
 // ReadTimestamp reads the first or next timestamp.
-func (it *TimestampIterator) ReadTimestamp(stream encoding.IStream) (bool, bool, error) {
+func (it *TimestampIterator) ReadTimestamp(stream *encoding.IStream) (bool, bool, error) {
 	it.PrevAnt = nil
 
 	var (
@@ -97,7 +98,7 @@ func (it *TimestampIterator) ReadTimestamp(stream encoding.IStream) (bool, bool,
 // ReadTimeUnit reads an encoded time unit and updates the iterator's state
 // accordingly. It is exposed as a public method so that callers can control
 // the encoding / decoding of the time unit on their own if they choose.
-func (it *TimestampIterator) ReadTimeUnit(stream encoding.IStream) error {
+func (it *TimestampIterator) ReadTimeUnit(stream *encoding.IStream) error {
 	tuBits, err := stream.ReadByte()
 	if err != nil {
 		return err
@@ -112,7 +113,7 @@ func (it *TimestampIterator) ReadTimeUnit(stream encoding.IStream) error {
 	return nil
 }
 
-func (it *TimestampIterator) readFirstTimestamp(stream encoding.IStream) error {
+func (it *TimestampIterator) readFirstTimestamp(stream *encoding.IStream) error {
 	ntBits, err := stream.ReadBits(64)
 	if err != nil {
 		return err
@@ -133,7 +134,7 @@ func (it *TimestampIterator) readFirstTimestamp(stream encoding.IStream) error {
 	return nil
 }
 
-func (it *TimestampIterator) readNextTimestamp(stream encoding.IStream) error {
+func (it *TimestampIterator) readNextTimestamp(stream *encoding.IStream) error {
 	dod, err := it.readMarkerOrDeltaOfDelta(stream)
 	if err != nil {
 		return err
@@ -144,7 +145,8 @@ func (it *TimestampIterator) readNextTimestamp(stream encoding.IStream) error {
 	return nil
 }
 
-func (it *TimestampIterator) tryReadMarker(stream encoding.IStream) (time.Duration, bool, error) {
+// nolint: gocyclo
+func (it *TimestampIterator) tryReadMarker(stream *encoding.IStream) (time.Duration, bool, error) {
 	opcodeAndValue, success := it.tryPeekBits(stream, it.numBits)
 	if !success {
 		return 0, false, nil
@@ -200,7 +202,9 @@ func (it *TimestampIterator) tryReadMarker(stream encoding.IStream) (time.Durati
 	}
 }
 
-func (it *TimestampIterator) readMarkerOrDeltaOfDelta(stream encoding.IStream) (time.Duration, error) {
+func (it *TimestampIterator) readMarkerOrDeltaOfDelta(
+	stream *encoding.IStream,
+) (time.Duration, error) {
 	if !it.SkipMarkers {
 		dod, success, err := it.tryReadMarker(stream)
 		if err != nil {
@@ -224,7 +228,9 @@ func (it *TimestampIterator) readMarkerOrDeltaOfDelta(stream encoding.IStream) (
 }
 
 func (it *TimestampIterator) readDeltaOfDelta(
-	stream encoding.IStream, tes encoding.TimeEncodingScheme) (time.Duration, error) {
+	stream *encoding.IStream,
+	tes encoding.TimeEncodingScheme,
+) (time.Duration, error) {
 	if it.TimeUnitChanged {
 		// NB(xichen): if the time unit has changed, always read 64 bits as normalized
 		// dod in nanoseconds.
@@ -254,12 +260,12 @@ func (it *TimestampIterator) readDeltaOfDelta(
 
 		cb = (cb << 1) | nextCB
 		if cb == buckets[i].Opcode() {
-			dodBits, err := stream.ReadBits(uint(buckets[i].NumValueBits()))
+			dodBits, err := stream.ReadBits(uint8(buckets[i].NumValueBits()))
 			if err != nil {
 				return 0, err
 			}
 
-			dod := encoding.SignExtend(dodBits, uint(buckets[i].NumValueBits()))
+			dod := encoding.SignExtend(dodBits, uint8(buckets[i].NumValueBits()))
 			timeUnit, err := it.TimeUnit.Value()
 			if err != nil {
 				return 0, nil
@@ -269,7 +275,7 @@ func (it *TimestampIterator) readDeltaOfDelta(
 		}
 	}
 
-	numValueBits := uint(tes.DefaultBucket().NumValueBits())
+	numValueBits := uint8(tes.DefaultBucket().NumValueBits())
 	dodBits, err := stream.ReadBits(numValueBits)
 	if err != nil {
 		return 0, err
@@ -283,7 +289,7 @@ func (it *TimestampIterator) readDeltaOfDelta(
 	return xtime.FromNormalizedDuration(dod, timeUnit), nil
 }
 
-func (it *TimestampIterator) readAnnotation(stream encoding.IStream) error {
+func (it *TimestampIterator) readAnnotation(stream *encoding.IStream) error {
 	antLen, err := it.readVarint(stream)
 	if err != nil {
 		return err
@@ -311,12 +317,12 @@ func (it *TimestampIterator) readAnnotation(stream encoding.IStream) error {
 	return nil
 }
 
-func (it *TimestampIterator) readVarint(stream encoding.IStream) (int, error) {
+func (it *TimestampIterator) readVarint(stream *encoding.IStream) (int, error) {
 	res, err := binary.ReadVarint(stream)
 	return int(res), err
 }
 
-func (it *TimestampIterator) tryPeekBits(stream encoding.IStream, numBits uint) (uint64, bool) {
+func (it *TimestampIterator) tryPeekBits(stream *encoding.IStream, numBits uint8) (uint64, bool) {
 	res, err := stream.PeekBits(numBits)
 	if err != nil {
 		return 0, false
diff --git a/src/dbnode/encoding/multi_reader_iterator_test.go b/src/dbnode/encoding/multi_reader_iterator_test.go
index a82ab1549f..c065d24489 100644
--- a/src/dbnode/encoding/multi_reader_iterator_test.go
+++ b/src/dbnode/encoding/multi_reader_iterator_test.go
@@ -22,7 +22,6 @@ package encoding
 
 import (
 	"fmt"
-	"io"
 	"testing"
 	"time"
 
@@ -287,7 +286,7 @@ func assertTestMultiReaderIterator(
 	test testMultiReader,
 ) {
 	type readerEntries struct {
-		reader  io.Reader
+		reader  xio.Reader64
 		entries *testMultiReaderEntries
 	}
 
@@ -315,8 +314,8 @@ func assertTestMultiReaderIterator(
 	}
 
 	var testIterators []*testIterator
-	var iteratorAlloc func(reader io.Reader, descr namespace.SchemaDescr) ReaderIterator
-	iteratorAlloc = func(reader io.Reader, descr namespace.SchemaDescr) ReaderIterator {
+	var iteratorAlloc func(xio.Reader64, namespace.SchemaDescr) ReaderIterator
+	iteratorAlloc = func(reader xio.Reader64, _ namespace.SchemaDescr) ReaderIterator {
 		for i := range entriesByReader {
 			if reader != entriesByReader[i].reader {
 				continue
@@ -331,7 +330,7 @@ func assertTestMultiReaderIterator(
 					}
 				}
 			}
-			it.onReset = func(r io.Reader, descr namespace.SchemaDescr) {
+			it.onReset = func(r xio.Reader64, descr namespace.SchemaDescr) {
 				newIt := iteratorAlloc(r, descr).(*testIterator)
 				*it = *newIt
 				// We close this here as we never actually use this iterator
diff --git a/src/dbnode/encoding/null.go b/src/dbnode/encoding/null.go
index 2dc914dcd6..35ce276912 100644
--- a/src/dbnode/encoding/null.go
+++ b/src/dbnode/encoding/null.go
@@ -22,7 +22,6 @@ package encoding
 
 import (
 	"fmt"
-	"io"
 	"time"
 
 	"github.com/m3db/m3/src/dbnode/namespace"
@@ -54,12 +53,12 @@ func (e *nullEncoder) LastEncoded() (ts.Datapoint, error) {
 func (e *nullEncoder) LastAnnotationChecksum() (uint64, error) {
 	return 0, fmt.Errorf("not implemented")
 }
-func (e *nullEncoder) Len() int                                                     { return 0 }
-func (e *nullEncoder) Seal()                                                        { e.sealed = true }
-func (e *nullEncoder) Reset(t time.Time, capacity int, descr namespace.SchemaDescr) {}
-func (e *nullEncoder) Close()                                                       {}
-func (e *nullEncoder) Discard() ts.Segment                                          { return ts.Segment{} }
-func (e *nullEncoder) DiscardReset(t time.Time, capacity int, descr namespace.SchemaDescr) ts.Segment {
+func (e *nullEncoder) Len() int                                    { return 0 }
+func (e *nullEncoder) Seal()                                       { e.sealed = true }
+func (e *nullEncoder) Reset(time.Time, int, namespace.SchemaDescr) {}
+func (e *nullEncoder) Close()                                      {}
+func (e *nullEncoder) Discard() ts.Segment                         { return ts.Segment{} }
+func (e *nullEncoder) DiscardReset(time.Time, int, namespace.SchemaDescr) ts.Segment {
 	return ts.Segment{}
 }
 func (e *nullEncoder) SetSchema(_ namespace.SchemaDescr) {}
@@ -74,7 +73,8 @@ func NewNullReaderIterator() ReaderIterator {
 func (r *nullReaderIterator) Current() (ts.Datapoint, xtime.Unit, ts.Annotation) {
 	return ts.Datapoint{}, xtime.Unit(0), nil
 }
-func (r *nullReaderIterator) Next() bool                                          { return false }
-func (r *nullReaderIterator) Err() error                                          { return fmt.Errorf("not implemented") }
-func (r *nullReaderIterator) Close()                                              {}
-func (r *nullReaderIterator) Reset(reader io.Reader, descr namespace.SchemaDescr) {}
+func (r *nullReaderIterator) Next() bool { return false }
+func (r *nullReaderIterator) Err() error { return fmt.Errorf("not implemented") }
+func (r *nullReaderIterator) Close()     {}
+func (r *nullReaderIterator) Reset(xio.Reader64, namespace.SchemaDescr) {
+}
diff --git a/src/dbnode/encoding/proto/corruption_prop_test.go b/src/dbnode/encoding/proto/corruption_prop_test.go
index 7f5ec5e5a9..c58ae0f78a 100644
--- a/src/dbnode/encoding/proto/corruption_prop_test.go
+++ b/src/dbnode/encoding/proto/corruption_prop_test.go
@@ -23,7 +23,6 @@
 package proto
 
 import (
-	"bytes"
 	"os"
 	"testing"
 	"time"
@@ -31,7 +30,9 @@ import (
 	"github.com/leanovate/gopter"
 	"github.com/leanovate/gopter/gen"
 	"github.com/leanovate/gopter/prop"
+
 	"github.com/m3db/m3/src/dbnode/namespace"
+	"github.com/m3db/m3/src/dbnode/x/xio"
 )
 
 // TestIteratorHandlesCorruptStreams ensures that the protobuf iterator never panics when reading corrupt streams.
@@ -48,8 +49,8 @@ func TestIteratorHandlesCorruptStreams(t *testing.T) {
 	parameters.Rng.Seed(seed)
 
 	props.Property("Iterator should handle corrupt streams", prop.ForAll(func(input corruptionPropTestInput) (bool, error) {
-		buff := bytes.NewBuffer(input.bytes)
-		iter := NewIterator(buff, namespace.GetTestSchemaDescr(testVLSchema), testEncodingOptions)
+		r := xio.NewBytesReader64(input.bytes)
+		iter := NewIterator(r, namespace.GetTestSchemaDescr(testVLSchema), testEncodingOptions)
 		for iter.Next() {
 		}
 		return true, nil
diff --git a/src/dbnode/encoding/proto/int_encoder_iterator.go b/src/dbnode/encoding/proto/int_encoder_iterator.go
index 53dc4074eb..d15e7c472e 100644
--- a/src/dbnode/encoding/proto/int_encoder_iterator.go
+++ b/src/dbnode/encoding/proto/int_encoder_iterator.go
@@ -27,10 +27,6 @@ import (
 	"github.com/m3db/m3/src/dbnode/encoding/m3tsz"
 )
 
-const (
-	opcodeZeroSig = 0x0
-)
-
 type intEncoderAndIterator struct {
 	prevIntBits       uint64
 	intSigBitsTracker m3tsz.IntSigBitsTracker
@@ -148,7 +144,7 @@ func (eit *intEncoderAndIterator) encodeIntValDiff(stream encoding.OStream, valB
 	stream.WriteBits(valBits, int(numSig))
 }
 
-func (eit *intEncoderAndIterator) readIntValue(stream encoding.IStream) error {
+func (eit *intEncoderAndIterator) readIntValue(stream *encoding.IStream) error {
 	if eit.hasEncodedFirst {
 		changeExistsControlBit, err := stream.ReadBit()
 		if err != nil {
@@ -182,7 +178,7 @@ func (eit *intEncoderAndIterator) readIntValue(stream encoding.IStream) error {
 	return nil
 }
 
-func (eit *intEncoderAndIterator) readIntSig(stream encoding.IStream) error {
+func (eit *intEncoderAndIterator) readIntSig(stream *encoding.IStream) error {
 	updateControlBit, err := stream.ReadBit()
 	if err != nil {
 		return fmt.Errorf(
@@ -216,7 +212,7 @@ func (eit *intEncoderAndIterator) readIntSig(stream encoding.IStream) error {
 	return nil
 }
 
-func (eit *intEncoderAndIterator) readIntValDiff(stream encoding.IStream) error {
+func (eit *intEncoderAndIterator) readIntValDiff(stream *encoding.IStream) error {
 	negativeControlBit, err := stream.ReadBit()
 	if err != nil {
 		return fmt.Errorf(
@@ -224,7 +220,7 @@ func (eit *intEncoderAndIterator) readIntValDiff(stream encoding.IStream) error
 			itErrPrefix, err)
 	}
 
-	numSig := uint(eit.intSigBitsTracker.NumSig)
+	numSig := eit.intSigBitsTracker.NumSig
 	diffSigBits, err := stream.ReadBits(numSig)
 	if err != nil {
 		return fmt.Errorf(
diff --git a/src/dbnode/encoding/proto/iterator.go b/src/dbnode/encoding/proto/iterator.go
index 54dbb68eda..d1c81ab575 100644
--- a/src/dbnode/encoding/proto/iterator.go
+++ b/src/dbnode/encoding/proto/iterator.go
@@ -30,6 +30,7 @@ import (
 	"github.com/m3db/m3/src/dbnode/encoding/m3tsz"
 	"github.com/m3db/m3/src/dbnode/namespace"
 	"github.com/m3db/m3/src/dbnode/ts"
+	"github.com/m3db/m3/src/dbnode/x/xio"
 	"github.com/m3db/m3/src/x/checked"
 	"github.com/m3db/m3/src/x/ident"
 	"github.com/m3db/m3/src/x/instrument"
@@ -55,7 +56,7 @@ type iterator struct {
 	err                  error
 	schema               *desc.MessageDescriptor
 	schemaDesc           namespace.SchemaDescr
-	stream               encoding.IStream
+	stream               *encoding.IStream
 	marshaller           customFieldMarshaller
 	byteFieldDictLRUSize int
 	// TODO(rartoul): Update these as we traverse the stream if we encounter
@@ -79,11 +80,11 @@ type iterator struct {
 
 // NewIterator creates a new iterator.
 func NewIterator(
-	reader io.Reader,
+	reader xio.Reader64,
 	descr namespace.SchemaDescr,
 	opts encoding.Options,
 ) encoding.ReaderIterator {
-	stream := encoding.NewIStream(reader, opts.IStreamReaderSizeProto())
+	stream := encoding.NewIStream(reader)
 
 	i := &iterator{
 		opts:       opts,
@@ -237,7 +238,7 @@ func (it *iterator) Err() error {
 	return it.err
 }
 
-func (it *iterator) Reset(reader io.Reader, descr namespace.SchemaDescr) {
+func (it *iterator) Reset(reader xio.Reader64, descr namespace.SchemaDescr) {
 	it.resetSchema(descr)
 	it.stream.Reset(reader)
 	it.tsIterator = m3tsz.NewTimestampIterator(it.opts, true)
@@ -336,7 +337,7 @@ func (it *iterator) readCustomFieldsSchema() error {
 	}
 
 	for i := 1; i <= int(numCustomFields); i++ {
-		fieldTypeBits, err := it.stream.ReadBits(uint(numBitsToEncodeCustomType))
+		fieldTypeBits, err := it.stream.ReadBits(uint8(numBitsToEncodeCustomType))
 		if err != nil {
 			return err
 		}
@@ -546,7 +547,7 @@ func (it *iterator) readBytesValue(i int, customField customFieldState) error {
 
 	if valueInDictControlBit == opCodeInterpretSubsequentBitsAsLRUIndex {
 		dictIdxBits, err := it.stream.ReadBits(
-			uint(numBitsRequiredForNumUpToN(it.byteFieldDictLRUSize)))
+			uint8(numBitsRequiredForNumUpToN(it.byteFieldDictLRUSize)))
 		if err != nil {
 			return fmt.Errorf(
 				"%s error trying to read bytes dict idx: %v",
@@ -861,15 +862,6 @@ func (it *iterator) nextToBeEvicted(fieldIdx int) []byte {
 	return dict[0]
 }
 
-func (it *iterator) readBits(numBits uint) (uint64, error) {
-	res, err := it.stream.ReadBits(numBits)
-	if err != nil {
-		return 0, err
-	}
-
-	return res, nil
-}
-
 func (it *iterator) resetUnmarshalProtoBuffer(n int) {
 	if it.unmarshalProtoBuf != nil && it.unmarshalProtoBuf.Cap() >= n {
 		// If the existing one is big enough, just resize it.
diff --git a/src/dbnode/encoding/proto/round_trip_test.go b/src/dbnode/encoding/proto/round_trip_test.go
index 7e0cb64f5c..3efdf25129 100644
--- a/src/dbnode/encoding/proto/round_trip_test.go
+++ b/src/dbnode/encoding/proto/round_trip_test.go
@@ -21,7 +21,6 @@
 package proto
 
 import (
-	"bytes"
 	"errors"
 	"fmt"
 	"testing"
@@ -30,6 +29,7 @@ import (
 	"github.com/m3db/m3/src/dbnode/encoding"
 	"github.com/m3db/m3/src/dbnode/namespace"
 	"github.com/m3db/m3/src/dbnode/ts"
+	"github.com/m3db/m3/src/dbnode/x/xio"
 	"github.com/m3db/m3/src/x/pool"
 	xtime "github.com/m3db/m3/src/x/time"
 
@@ -162,8 +162,8 @@ func TestRoundTrip(t *testing.T) {
 	require.NoError(t, err)
 	require.Equal(t, numExpectedBytes, len(rawBytes))
 
-	buff := bytes.NewBuffer(rawBytes)
-	iter := NewIterator(buff, namespace.GetTestSchemaDescr(testVLSchema), testEncodingOptions)
+	r := xio.NewBytesReader64(rawBytes)
+	iter := NewIterator(r, namespace.GetTestSchemaDescr(testVLSchema), testEncodingOptions)
 
 	i := 0
 	for iter.Next() {
@@ -212,9 +212,9 @@ func TestRoundTripMidStreamSchemaChanges(t *testing.T) {
 
 	vl2WriteTime := vl1WriteTime.Add(time.Second)
 	err = enc.Encode(ts.Datapoint{Timestamp: vl2WriteTime}, xtime.Second, marshalledVL)
-	require.Equal(t,
-		"proto encoder: error unmarshalling message: encountered unknown field with field number: 6",
-		err.Error())
+	require.EqualError(t,
+		err,
+		"proto encoder: error unmarshalling message: encountered unknown field with field number: 6")
 
 	enc.SetSchema(namespace.GetTestSchemaDescr(testVL2Schema))
 	err = enc.Encode(ts.Datapoint{Timestamp: vl2WriteTime}, xtime.Second, marshalledVL)
@@ -224,8 +224,8 @@ func TestRoundTripMidStreamSchemaChanges(t *testing.T) {
 	require.NoError(t, err)
 
 	// Try reading the stream just using the vl1 schema.
-	buff := bytes.NewBuffer(rawBytes)
-	iter := NewIterator(buff, namespace.GetTestSchemaDescr(testVLSchema), testEncodingOptions)
+	r := xio.NewBytesReader64(rawBytes)
+	iter := NewIterator(r, namespace.GetTestSchemaDescr(testVLSchema), testEncodingOptions)
 
 	require.True(t, iter.Next(), "iter err: %v", iter.Err())
 	dp, unit, annotation := iter.Current()
@@ -260,8 +260,8 @@ func TestRoundTripMidStreamSchemaChanges(t *testing.T) {
 	require.NoError(t, iter.Err())
 
 	// Try reading the stream just using the vl2 schema.
-	buff = bytes.NewBuffer(rawBytes)
-	iter = NewIterator(buff, namespace.GetTestSchemaDescr(testVL2Schema), testEncodingOptions)
+	r = xio.NewBytesReader64(rawBytes)
+	iter = NewIterator(r, namespace.GetTestSchemaDescr(testVL2Schema), testEncodingOptions)
 
 	require.True(t, iter.Next(), "iter err: %v", iter.Err())
 	dp, unit, annotation = iter.Current()
diff --git a/src/dbnode/encoding/scheme.go b/src/dbnode/encoding/scheme.go
index efcbcee138..0c8327aea8 100644
--- a/src/dbnode/encoding/scheme.go
+++ b/src/dbnode/encoding/scheme.go
@@ -141,7 +141,8 @@ func newTimeEncodingSchemes(schemes map[xtime.Unit]TimeEncodingScheme) TimeEncod
 }
 
 // newTimeEncodingScheme creates a new time encoding scheme.
-// NB(xichen): numValueBitsForBbuckets should be ordered by value in ascending order (smallest value first).
+// NB(xichen): numValueBitsForBuckets should be ordered by value
+// in ascending order (smallest value first).
 func newTimeEncodingScheme(numValueBitsForBuckets []int, numValueBitsForDefault int) TimeEncodingScheme {
 	numBuckets := len(numValueBitsForBuckets)
 	buckets := make([]TimeBucket, 0, numBuckets)
diff --git a/src/dbnode/encoding/series_iterator_split_into_blocks_test.go b/src/dbnode/encoding/series_iterator_split_into_blocks_test.go
index 5ebc2aadd8..5ef4e7d7a2 100644
--- a/src/dbnode/encoding/series_iterator_split_into_blocks_test.go
+++ b/src/dbnode/encoding/series_iterator_split_into_blocks_test.go
@@ -22,7 +22,6 @@
 package encoding_test
 
 import (
-	"io"
 	"testing"
 	"time"
 
@@ -34,9 +33,10 @@ import (
 	"github.com/m3db/m3/src/x/ident"
 	xtime "github.com/m3db/m3/src/x/time"
 
-	"github.com/m3db/m3/src/dbnode/namespace"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
+
+	"github.com/m3db/m3/src/dbnode/namespace"
 )
 
 type Series struct {
@@ -69,7 +69,7 @@ func TestDeconstructAndReconstruct(t *testing.T) {
 		i++
 	}
 
-	iterAlloc := func(r io.Reader, _ namespace.SchemaDescr) encoding.ReaderIterator {
+	iterAlloc := func(r xio.Reader64, _ namespace.SchemaDescr) encoding.ReaderIterator {
 		iter := m3tsz.NewDecoder(true, encoding.NewOptions())
 		return iter.Decode(r)
 	}
diff --git a/src/dbnode/encoding/types.go b/src/dbnode/encoding/types.go
index 230925b340..567d908016 100644
--- a/src/dbnode/encoding/types.go
+++ b/src/dbnode/encoding/types.go
@@ -21,7 +21,6 @@
 package encoding
 
 import (
-	"io"
 	"time"
 
 	"github.com/m3db/m3/src/dbnode/namespace"
@@ -151,19 +150,19 @@ type Options interface {
 	// ByteFieldDictionaryLRUSize returns the ByteFieldDictionaryLRUSize.
 	ByteFieldDictionaryLRUSize() int
 
-	// SetIStreamReaderSizeM3TSZ sets the istream bufio reader size
+	// SetIStreamReaderSizeM3TSZ sets the IStream bufio reader size
 	// for m3tsz encoding iteration.
 	SetIStreamReaderSizeM3TSZ(value int) Options
 
-	// IStreamReaderSizeM3TSZ returns the istream bufio reader size
+	// IStreamReaderSizeM3TSZ returns the IStream bufio reader size
 	// for m3tsz encoding iteration.
 	IStreamReaderSizeM3TSZ() int
 
-	// SetIStreamReaderSizeProto sets the istream bufio reader size
+	// SetIStreamReaderSizeProto sets the IStream bufio reader size
 	// for proto encoding iteration.
 	SetIStreamReaderSizeProto(value int) Options
 
-	// SetIStreamReaderSizeProto returns the istream bufio reader size
+	// SetIStreamReaderSizeProto returns the IStream bufio reader size
 	// for proto encoding iteration.
 	IStreamReaderSizeProto() int
 }
@@ -191,7 +190,7 @@ type ReaderIterator interface {
 
 	// Reset resets the iterator to read from a new reader with
 	// a new schema (for schema aware iterators).
-	Reset(reader io.Reader, schema namespace.SchemaDescr)
+	Reset(reader xio.Reader64, schema namespace.SchemaDescr)
 }
 
 // MultiReaderIterator is an iterator that iterates in order over
@@ -328,7 +327,7 @@ type MutableSeriesIterators interface {
 // Decoder is the generic interface for different types of decoders.
 type Decoder interface {
 	// Decode decodes the encoded data in the reader.
-	Decode(reader io.Reader) ReaderIterator
+	Decode(reader xio.Reader64) ReaderIterator
 }
 
 // NewDecoderFn creates a new decoder.
@@ -338,32 +337,7 @@ type NewDecoderFn func() Decoder
 type EncoderAllocate func() Encoder
 
 // ReaderIteratorAllocate allocates a ReaderIterator for a pool.
-type ReaderIteratorAllocate func(reader io.Reader, descr namespace.SchemaDescr) ReaderIterator
-
-// IStream encapsulates a readable stream.
-type IStream interface {
-	// Read reads len(b) bytes.
-	Read([]byte) (int, error)
-
-	// ReadBit reads the next Bit.
-	ReadBit() (Bit, error)
-
-	// ReadByte reads the next Byte.
-	ReadByte() (byte, error)
-
-	// ReadBits reads the next Bits.
-	ReadBits(numBits uint) (uint64, error)
-
-	// PeekBits looks at the next Bits, but doesn't move the pos.
-	PeekBits(numBits uint) (uint64, error)
-
-	// RemainingBitsInCurrentByte returns the number of bits remaining to
-	// be read in the current byte.
-	RemainingBitsInCurrentByte() uint
-
-	// Reset resets the IStream.
-	Reset(r io.Reader)
-}
+type ReaderIteratorAllocate func(reader xio.Reader64, descr namespace.SchemaDescr) ReaderIterator
 
 // OStream encapsulates a writable stream.
 type OStream interface {
diff --git a/src/dbnode/integration/disk_flush_helpers.go b/src/dbnode/integration/disk_flush_helpers.go
index be56b6a327..661eda8518 100644
--- a/src/dbnode/integration/disk_flush_helpers.go
+++ b/src/dbnode/integration/disk_flush_helpers.go
@@ -23,7 +23,6 @@
 package integration
 
 import (
-	"bytes"
 	"errors"
 	"fmt"
 	"testing"
@@ -36,6 +35,7 @@ import (
 	"github.com/m3db/m3/src/dbnode/persist/fs"
 	"github.com/m3db/m3/src/dbnode/sharding"
 	"github.com/m3db/m3/src/dbnode/storage"
+	"github.com/m3db/m3/src/dbnode/x/xio"
 	"github.com/m3db/m3/src/x/ident"
 	"github.com/m3db/m3/src/x/ident/testutil"
 	xtime "github.com/m3db/m3/src/x/time"
@@ -184,14 +184,6 @@ func waitUntilFileSetFilesExist(
 	return waitUntilFileSetFilesExistOrNot(filePathPrefix, files, true, timeout)
 }
 
-func waitUntilFileSetFilesNotExist(
-	filePathPrefix string,
-	files []fs.FileSetFileIdentifier,
-	timeout time.Duration,
-) error {
-	return waitUntilFileSetFilesExistOrNot(filePathPrefix, files, false, timeout)
-}
-
 func waitUntilFileSetFilesExistOrNot(
 	filePathPrefix string,
 	files []fs.FileSetFileIdentifier,
@@ -309,7 +301,7 @@ func checkForTime(
 
 			var datapoints []generate.TestValue
 			it := iteratorPool.Get()
-			it.Reset(bytes.NewBuffer(data.Bytes()), nsCtx.Schema)
+			it.Reset(xio.NewBytesReader64(data.Bytes()), nsCtx.Schema)
 			for it.Next() {
 				dp, _, ann := it.Current()
 				datapoints = append(datapoints, generate.TestValue{Datapoint: dp, Annotation: ann})
diff --git a/src/dbnode/persist/fs/merger_test.go b/src/dbnode/persist/fs/merger_test.go
index 9487e4b09a..5592274538 100644
--- a/src/dbnode/persist/fs/merger_test.go
+++ b/src/dbnode/persist/fs/merger_test.go
@@ -75,9 +75,7 @@ func init() {
 	srPool = xio.NewSegmentReaderPool(poolOpts)
 	srPool.Init()
 	multiIterPool = encoding.NewMultiReaderIteratorPool(poolOpts)
-	multiIterPool.Init(func(r io.Reader, _ namespace.SchemaDescr) encoding.ReaderIterator {
-		return m3tsz.NewReaderIterator(r, m3tsz.DefaultIntOptimizationEnabled, encoding.NewOptions())
-	})
+	multiIterPool.Init(m3tsz.DefaultReaderIteratorAllocFn(encoding.NewOptions()))
 	bytesPool := pool.NewCheckedBytesPool(nil, poolOpts, func(s []pool.Bucket) pool.BytesPool {
 		return pool.NewBytesPool(s, poolOpts)
 	})
@@ -618,11 +616,10 @@ func datapointsToCheckedBytes(t *testing.T, dps []ts.Datapoint) checked.Bytes {
 
 	r, ok := encoder.Stream(ctx)
 	require.True(t, ok)
-	var b [1000]byte
-	n, err := r.Read(b[:])
-	require.NoError(t, err)
+	bytes, err := xio.ToBytes(r)
+	require.Equal(t, io.EOF, err)
 
-	copied := append([]byte(nil), b[:n]...)
+	copied := append([]byte(nil), bytes...)
 	cb := checked.NewBytes(copied, nil)
 	return cb
 }
diff --git a/src/dbnode/persist/fs/retriever.go b/src/dbnode/persist/fs/retriever.go
index 8f725866ec..fc15887c22 100644
--- a/src/dbnode/persist/fs/retriever.go
+++ b/src/dbnode/persist/fs/retriever.go
@@ -969,12 +969,20 @@ func (req *retrieveRequest) BlockSize() time.Duration {
 	return req.blockSize
 }
 
-func (req *retrieveRequest) Read(b []byte) (int, error) {
+func (req *retrieveRequest) Read64() (word uint64, n byte, err error) {
 	req.resultWg.Wait()
 	if req.err != nil {
-		return 0, req.err
+		return 0, 0, req.err
 	}
-	return req.reader.Read(b)
+	return req.reader.Read64()
+}
+
+func (req *retrieveRequest) Peek64() (word uint64, n byte, err error) {
+	req.resultWg.Wait()
+	if req.err != nil {
+		return 0, 0, req.err
+	}
+	return req.reader.Peek64()
 }
 
 func (req *retrieveRequest) Segment() (ts.Segment, error) {
diff --git a/src/dbnode/server/server.go b/src/dbnode/server/server.go
index 13ab1ac9ef..c02f8caef7 100644
--- a/src/dbnode/server/server.go
+++ b/src/dbnode/server/server.go
@@ -1683,14 +1683,14 @@ func withEncodingAndPoolingOptions(
 		return m3tsz.NewEncoder(time.Time{}, nil, m3tsz.DefaultIntOptimizationEnabled, encodingOpts)
 	})
 
-	iteratorPool.Init(func(r io.Reader, descr namespace.SchemaDescr) encoding.ReaderIterator {
+	iteratorPool.Init(func(r xio.Reader64, descr namespace.SchemaDescr) encoding.ReaderIterator {
 		if cfg.Proto != nil && cfg.Proto.Enabled {
 			return proto.NewIterator(r, descr, encodingOpts)
 		}
 		return m3tsz.NewReaderIterator(r, m3tsz.DefaultIntOptimizationEnabled, encodingOpts)
 	})
 
-	multiIteratorPool.Init(func(r io.Reader, descr namespace.SchemaDescr) encoding.ReaderIterator {
+	multiIteratorPool.Init(func(r xio.Reader64, descr namespace.SchemaDescr) encoding.ReaderIterator {
 		iter := iteratorPool.Get()
 		iter.Reset(r, descr)
 		return iter
diff --git a/src/dbnode/storage/block/merged_block_reader.go b/src/dbnode/storage/block/merged_block_reader.go
index 04461f261f..cd3b90e39e 100644
--- a/src/dbnode/storage/block/merged_block_reader.go
+++ b/src/dbnode/storage/block/merged_block_reader.go
@@ -177,12 +177,20 @@ func (r *dbMergedBlockReader) BlockSize() time.Duration {
 	return r.blockSize
 }
 
-func (r *dbMergedBlockReader) Read(b []byte) (int, error) {
+func (r *dbMergedBlockReader) Read64() (word uint64, n byte, err error) {
 	reader, err := r.mergedReader()
 	if err != nil {
-		return 0, err
+		return 0, 0, err
 	}
-	return reader.Read(b)
+	return reader.Read64()
+}
+
+func (r *dbMergedBlockReader) Peek64() (word uint64, n byte, err error) {
+	reader, err := r.mergedReader()
+	if err != nil {
+		return 0, 0, err
+	}
+	return reader.Peek64()
 }
 
 func (r *dbMergedBlockReader) Segment() (ts.Segment, error) {
diff --git a/src/dbnode/storage/block/options.go b/src/dbnode/storage/block/options.go
index 70abd04930..14e1581db7 100644
--- a/src/dbnode/storage/block/options.go
+++ b/src/dbnode/storage/block/options.go
@@ -21,17 +21,15 @@
 package block
 
 import (
-	"io"
-
 	"github.com/m3db/m3/src/dbnode/encoding"
 	"github.com/m3db/m3/src/dbnode/encoding/m3tsz"
+	"github.com/m3db/m3/src/dbnode/namespace"
 	"github.com/m3db/m3/src/dbnode/ts"
 	"github.com/m3db/m3/src/dbnode/x/xio"
 	"github.com/m3db/m3/src/x/clock"
 	"github.com/m3db/m3/src/x/context"
 	"github.com/m3db/m3/src/x/pool"
 	xsync "github.com/m3db/m3/src/x/sync"
-	"github.com/m3db/m3/src/dbnode/namespace"
 )
 
 const (
@@ -93,14 +91,13 @@ func NewOptions() Options {
 	o.encoderPool.Init(func() encoding.Encoder {
 		return m3tsz.NewEncoder(timeZero, nil, m3tsz.DefaultIntOptimizationEnabled, encodingOpts)
 	})
-	o.readerIteratorPool.Init(func(r io.Reader, descr namespace.SchemaDescr) encoding.ReaderIterator {
-		return m3tsz.NewReaderIterator(r, m3tsz.DefaultIntOptimizationEnabled, encodingOpts)
-	})
-	o.multiReaderIteratorPool.Init(func(r io.Reader, descr namespace.SchemaDescr) encoding.ReaderIterator {
-		it := o.readerIteratorPool.Get()
-		it.Reset(r, descr)
-		return it
-	})
+	o.readerIteratorPool.Init(m3tsz.DefaultReaderIteratorAllocFn(encodingOpts))
+	o.multiReaderIteratorPool.Init(
+		func(r xio.Reader64, descr namespace.SchemaDescr) encoding.ReaderIterator {
+			it := o.readerIteratorPool.Get()
+			it.Reset(r, descr)
+			return it
+		})
 	o.segmentReaderPool.Init()
 	o.bytesPool.Init()
 	return o
diff --git a/src/dbnode/storage/bootstrap/bootstrapper/commitlog/source_data_test.go b/src/dbnode/storage/bootstrap/bootstrapper/commitlog/source_data_test.go
index 146266966a..21d8724a4c 100644
--- a/src/dbnode/storage/bootstrap/bootstrapper/commitlog/source_data_test.go
+++ b/src/dbnode/storage/bootstrap/bootstrapper/commitlog/source_data_test.go
@@ -36,6 +36,7 @@ import (
 	"github.com/m3db/m3/src/dbnode/storage/series"
 	"github.com/m3db/m3/src/dbnode/topology"
 	"github.com/m3db/m3/src/dbnode/ts"
+	"github.com/m3db/m3/src/dbnode/x/xio"
 	"github.com/m3db/m3/src/x/checked"
 	"github.com/m3db/m3/src/x/context"
 	"github.com/m3db/m3/src/x/ident"
@@ -441,9 +442,9 @@ func testItMergesSnapshotsAndCommitLogs(t *testing.T, opts Options,
 	seg, err := reader.Segment()
 	require.NoError(t, err)
 
-	bytes := make([]byte, seg.Len())
-	_, err = reader.Read(bytes)
-	require.NoError(t, err)
+	bytes, err := xio.ToBytes(reader)
+	require.Equal(t, io.EOF, err)
+	require.Equal(t, seg.Len(), len(bytes))
 
 	mockReader.EXPECT().Read().Return(
 		foo.ID,
diff --git a/src/dbnode/storage/bootstrap/bootstrapper/commitlog/source_prop_test.go b/src/dbnode/storage/bootstrap/bootstrapper/commitlog/source_prop_test.go
index 7c689dc4d2..57146b5786 100644
--- a/src/dbnode/storage/bootstrap/bootstrapper/commitlog/source_prop_test.go
+++ b/src/dbnode/storage/bootstrap/bootstrapper/commitlog/source_prop_test.go
@@ -24,6 +24,7 @@ package commitlog
 
 import (
 	"fmt"
+	"io"
 	"io/ioutil"
 	"os"
 	"reflect"
@@ -45,6 +46,7 @@ import (
 	"github.com/m3db/m3/src/dbnode/topology"
 	tu "github.com/m3db/m3/src/dbnode/topology/testutil"
 	"github.com/m3db/m3/src/dbnode/ts"
+	"github.com/m3db/m3/src/dbnode/x/xio"
 	"github.com/m3db/m3/src/x/checked"
 	"github.com/m3db/m3/src/x/context"
 	"github.com/m3db/m3/src/x/ident"
@@ -191,14 +193,8 @@ func TestCommitLogSourcePropCorrectlyBootstrapsFromCommitlog(t *testing.T) {
 					ctx := context.NewBackground()
 					reader, ok := encoder.Stream(ctx)
 					if ok {
-						seg, err := reader.Segment()
-						if err != nil {
-							return false, err
-						}
-
-						bytes := make([]byte, seg.Len())
-						_, err = reader.Read(bytes)
-						if err != nil {
+						bytes, err := xio.ToBytes(reader)
+						if err != io.EOF {
 							return false, err
 						}
 						encodersBySeries[seriesID] = bytes
diff --git a/src/dbnode/storage/bootstrap/bootstrapper/fs/source_data_test.go b/src/dbnode/storage/bootstrap/bootstrapper/fs/source_data_test.go
index 907e3b5a47..7b2eb03f40 100644
--- a/src/dbnode/storage/bootstrap/bootstrapper/fs/source_data_test.go
+++ b/src/dbnode/storage/bootstrap/bootstrapper/fs/source_data_test.go
@@ -23,6 +23,7 @@ package fs
 import (
 	"errors"
 	"fmt"
+	"io"
 	"io/ioutil"
 	"os"
 	"path"
@@ -44,6 +45,7 @@ import (
 	"github.com/m3db/m3/src/dbnode/storage/index"
 	"github.com/m3db/m3/src/dbnode/storage/index/compaction"
 	"github.com/m3db/m3/src/dbnode/storage/series"
+	"github.com/m3db/m3/src/dbnode/x/xio"
 	"github.com/m3db/m3/src/m3ninx/index/segment/fst"
 	"github.com/m3db/m3/src/x/checked"
 	"github.com/m3db/m3/src/x/context"
@@ -557,11 +559,10 @@ func validateReadResults(
 		readerAtTime := seriesReaders[0]
 		assert.Equal(t, times[i], readerAtTime.Start)
 		ctx := context.NewBackground()
-		var b [100]byte
-		n, err := readerAtTime.Reader.Read(b[:])
+		bytes, err := xio.ToBytes(readerAtTime.Reader)
 		ctx.Close()
-		require.NoError(t, err)
-		require.Equal(t, data[i], b[:n])
+		require.Equal(t, io.EOF, err)
+		require.Equal(t, data[i], bytes)
 	}
 
 	tester.EnsureNoWrites()
diff --git a/src/dbnode/storage/bootstrap/util.go b/src/dbnode/storage/bootstrap/util.go
index 2019b1d49a..877b059d8d 100644
--- a/src/dbnode/storage/bootstrap/util.go
+++ b/src/dbnode/storage/bootstrap/util.go
@@ -316,12 +316,7 @@ type NamespacesTester struct {
 
 func buildDefaultIterPool() encoding.MultiReaderIteratorPool {
 	iterPool := encoding.NewMultiReaderIteratorPool(pool.NewObjectPoolOptions())
-	iterPool.Init(
-		func(r io.Reader, _ namespace.SchemaDescr) encoding.ReaderIterator {
-			return m3tsz.NewReaderIterator(r,
-				m3tsz.DefaultIntOptimizationEnabled,
-				encoding.NewOptions())
-		})
+	iterPool.Init(m3tsz.DefaultReaderIteratorAllocFn(encoding.NewOptions()))
 	return iterPool
 }
 
diff --git a/src/dbnode/storage/options.go b/src/dbnode/storage/options.go
index e276ee852a..ec56c22bda 100644
--- a/src/dbnode/storage/options.go
+++ b/src/dbnode/storage/options.go
@@ -23,7 +23,6 @@ package storage
 import (
 	"errors"
 	"fmt"
-	"io"
 	"math"
 	"runtime"
 	"time"
@@ -505,16 +504,12 @@ func (o *options) SetEncodingM3TSZPooled() Options {
 	opts.encoderPool = encoderPool
 
 	// initialize single reader iterator pool
-	readerIteratorPool.Init(func(r io.Reader, descr namespace.SchemaDescr) encoding.ReaderIterator {
-		return m3tsz.NewReaderIterator(r, m3tsz.DefaultIntOptimizationEnabled, encodingOpts)
-	})
+	readerIteratorPool.Init(m3tsz.DefaultReaderIteratorAllocFn(encodingOpts))
 	opts.readerIteratorPool = readerIteratorPool
 
 	// initialize multi reader iterator pool
 	multiReaderIteratorPool := encoding.NewMultiReaderIteratorPool(opts.poolOpts)
-	multiReaderIteratorPool.Init(func(r io.Reader, descr namespace.SchemaDescr) encoding.ReaderIterator {
-		return m3tsz.NewReaderIterator(r, m3tsz.DefaultIntOptimizationEnabled, encodingOpts)
-	})
+	multiReaderIteratorPool.Init(m3tsz.DefaultReaderIteratorAllocFn(encodingOpts))
 	opts.multiReaderIteratorPool = multiReaderIteratorPool
 
 	opts.blockOpts = opts.blockOpts.
diff --git a/src/dbnode/storage/series/buffer_test.go b/src/dbnode/storage/series/buffer_test.go
index 8497b451dc..87bd5cfece 100644
--- a/src/dbnode/storage/series/buffer_test.go
+++ b/src/dbnode/storage/series/buffer_test.go
@@ -21,7 +21,6 @@
 package series
 
 import (
-	"io"
 	"sort"
 	"strings"
 	"testing"
@@ -42,9 +41,10 @@ import (
 	xtime "github.com/m3db/m3/src/x/time"
 
 	"github.com/golang/mock/gomock"
-	"github.com/m3db/m3/src/dbnode/namespace"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
+
+	"github.com/m3db/m3/src/dbnode/namespace"
 )
 
 var (
@@ -60,9 +60,7 @@ func newBufferTestOptions() Options {
 	encoderPool.Init(func() encoding.Encoder {
 		return m3tsz.NewEncoder(timeZero, nil, m3tsz.DefaultIntOptimizationEnabled, encodingOpts)
 	})
-	multiReaderIteratorPool.Init(func(r io.Reader, descr namespace.SchemaDescr) encoding.ReaderIterator {
-		return m3tsz.NewReaderIterator(r, m3tsz.DefaultIntOptimizationEnabled, encodingOpts)
-	})
+	multiReaderIteratorPool.Init(m3tsz.DefaultReaderIteratorAllocFn(encodingOpts))
 
 	bufferBucketPool := NewBufferBucketPool(nil)
 	bufferBucketVersionsPool := NewBufferBucketVersionsPool(nil)
diff --git a/src/dbnode/storage/series/series_test.go b/src/dbnode/storage/series/series_test.go
index f8d9e8e739..cd52c30c4f 100644
--- a/src/dbnode/storage/series/series_test.go
+++ b/src/dbnode/storage/series/series_test.go
@@ -22,7 +22,6 @@ package series
 
 import (
 	"errors"
-	"io"
 	"sort"
 	"testing"
 	"time"
@@ -43,9 +42,10 @@ import (
 	xtime "github.com/m3db/m3/src/x/time"
 
 	"github.com/golang/mock/gomock"
-	"github.com/m3db/m3/src/dbnode/namespace"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
+
+	"github.com/m3db/m3/src/dbnode/namespace"
 )
 
 func newSeriesTestOptions() Options {
@@ -57,9 +57,7 @@ func newSeriesTestOptions() Options {
 	encoderPool.Init(func() encoding.Encoder {
 		return m3tsz.NewEncoder(timeZero, nil, m3tsz.DefaultIntOptimizationEnabled, encodingOpts)
 	})
-	multiReaderIteratorPool.Init(func(r io.Reader, descr namespace.SchemaDescr) encoding.ReaderIterator {
-		return m3tsz.NewReaderIterator(r, m3tsz.DefaultIntOptimizationEnabled, encodingOpts)
-	})
+	multiReaderIteratorPool.Init(m3tsz.DefaultReaderIteratorAllocFn(encodingOpts))
 
 	bufferBucketPool := NewBufferBucketPool(nil)
 	bufferBucketVersionsPool := NewBufferBucketVersionsPool(nil)
diff --git a/src/dbnode/testdata/prototest/pools.go b/src/dbnode/testdata/prototest/pools.go
index 6b23f0e132..ad07221680 100644
--- a/src/dbnode/testdata/prototest/pools.go
+++ b/src/dbnode/testdata/prototest/pools.go
@@ -21,12 +21,12 @@
 package prototest
 
 import (
-	"io"
 	"time"
 
-	"github.com/m3db/m3/src/x/pool"
-	"github.com/m3db/m3/src/dbnode/encoding/proto"
 	"github.com/m3db/m3/src/dbnode/encoding"
+	"github.com/m3db/m3/src/dbnode/encoding/proto"
+	"github.com/m3db/m3/src/dbnode/x/xio"
+	"github.com/m3db/m3/src/x/pool"
 	xtime "github.com/m3db/m3/src/x/time"
 
 	"github.com/m3db/m3/src/dbnode/namespace"
@@ -63,10 +63,10 @@ func newPools() Pools {
 	encoderPool.Init(func() encoding.Encoder {
 		return proto.NewEncoder(timeZero, encodingOpts)
 	})
-	readerIterPool.Init(func(r io.Reader, descr namespace.SchemaDescr) encoding.ReaderIterator {
+	readerIterPool.Init(func(r xio.Reader64, descr namespace.SchemaDescr) encoding.ReaderIterator {
 		return proto.NewIterator(r, descr, encodingOpts)
 	})
-	multiReaderIteratorPool.Init(func(r io.Reader, descr namespace.SchemaDescr) encoding.ReaderIterator {
+	multiReaderIteratorPool.Init(func(r xio.Reader64, descr namespace.SchemaDescr) encoding.ReaderIterator {
 		i := readerIterPool.Get()
 		i.Reset(r, descr)
 		return i
diff --git a/src/dbnode/x/xio/block_reader_test.go b/src/dbnode/x/xio/block_reader_test.go
index fd7371a7cb..746822391a 100644
--- a/src/dbnode/x/xio/block_reader_test.go
+++ b/src/dbnode/x/xio/block_reader_test.go
@@ -50,16 +50,15 @@ func TestCloneBlock(t *testing.T) {
 	ctrl := gomock.NewController(t)
 	defer ctrl.Finish()
 
-	var p []byte
 	seg := ts.Segment{}
 
 	reader := NewMockSegmentReader(ctrl)
-	reader.EXPECT().Read(p).Return(0, errTest).Times(1)
-	reader.EXPECT().Read(p).Return(100, nil).Times(1)
+	reader.EXPECT().Read64().Return(uint64(0), byte(0), errTest).Times(1)
+	reader.EXPECT().Read64().Return(uint64(123456), byte(10), nil).Times(1)
 	reader.EXPECT().Reset(seg).Return().Times(1)
 
 	clonedReader := NewMockSegmentReader(ctrl)
-	clonedReader.EXPECT().Read(p).Return(1337, nil).Times(1)
+	clonedReader.EXPECT().Read64().Return(uint64(1337), byte(2), nil).Times(1)
 
 	reader.EXPECT().Clone(nil).Return(clonedReader, nil).Times(1)
 
@@ -69,12 +68,14 @@ func TestCloneBlock(t *testing.T) {
 		BlockSize:     blockSize,
 	}
 
-	read, err := b.Read(p)
-	require.Equal(t, read, 0)
-	require.Equal(t, err, errTest)
+	word, n, err := b.Read64()
+	require.Equal(t, uint64(0), word)
+	require.Equal(t, byte(0), n)
+	require.Equal(t, errTest, err)
 
-	read, err = b.Read(p)
-	require.Equal(t, read, 100)
+	word, n, err = b.Read64()
+	require.Equal(t, uint64(123456), word)
+	require.Equal(t, byte(10), n)
 	require.NoError(t, err)
 
 	b2, err := b.CloneBlock(nil)
@@ -90,9 +91,10 @@ func TestCloneBlock(t *testing.T) {
 	require.Equal(t, b2.Start, start)
 	require.Equal(t, b2.BlockSize, blockSize)
 
-	read, err = b2.Read(p)
+	word, n, err = b2.Read64()
 
-	require.Equal(t, read, 1337)
+	require.Equal(t, uint64(1337), word)
+	require.Equal(t, byte(2), n)
 	require.NoError(t, err)
 }
 
@@ -121,16 +123,16 @@ func TestBlockReaderClone(t *testing.T) {
 func TestBlockReaderRead(t *testing.T) {
 	br, sr := buildBlock(t)
 
-	var p []byte
-
-	sr.EXPECT().Read(p).Return(0, errTest).Times(1)
-	read, err := br.Read(p)
-	require.Equal(t, read, 0)
+	sr.EXPECT().Read64().Return(uint64(0), byte(0), errTest).Times(1)
+	word, n, err := br.Read64()
+	require.Equal(t, uint64(0), word)
+	require.Equal(t, byte(0), n)
 	require.Equal(t, err, errTest)
 
-	sr.EXPECT().Read(p).Return(100, nil).Times(1)
-	read, err = br.Read(p)
-	require.Equal(t, read, 100)
+	sr.EXPECT().Read64().Return(uint64(100), byte(1), nil).Times(1)
+	word, n, err = br.Read64()
+	require.Equal(t, uint64(100), word)
+	require.Equal(t, byte(1), n)
 	require.NoError(t, err)
 }
 
diff --git a/src/dbnode/x/xio/io_mock.go b/src/dbnode/x/xio/io_mock.go
index daa99ba481..12f1c91cc7 100644
--- a/src/dbnode/x/xio/io_mock.go
+++ b/src/dbnode/x/xio/io_mock.go
@@ -83,19 +83,36 @@ func (mr *MockSegmentReaderMockRecorder) Finalize() *gomock.Call {
 	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "Finalize", reflect.TypeOf((*MockSegmentReader)(nil).Finalize))
 }
 
-// Read mocks base method
-func (m *MockSegmentReader) Read(arg0 []byte) (int, error) {
+// Peek64 mocks base method
+func (m *MockSegmentReader) Peek64() (uint64, byte, error) {
 	m.ctrl.T.Helper()
-	ret := m.ctrl.Call(m, "Read", arg0)
-	ret0, _ := ret[0].(int)
-	ret1, _ := ret[1].(error)
-	return ret0, ret1
+	ret := m.ctrl.Call(m, "Peek64")
+	ret0, _ := ret[0].(uint64)
+	ret1, _ := ret[1].(byte)
+	ret2, _ := ret[2].(error)
+	return ret0, ret1, ret2
+}
+
+// Peek64 indicates an expected call of Peek64
+func (mr *MockSegmentReaderMockRecorder) Peek64() *gomock.Call {
+	mr.mock.ctrl.T.Helper()
+	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "Peek64", reflect.TypeOf((*MockSegmentReader)(nil).Peek64))
+}
+
+// Read64 mocks base method
+func (m *MockSegmentReader) Read64() (uint64, byte, error) {
+	m.ctrl.T.Helper()
+	ret := m.ctrl.Call(m, "Read64")
+	ret0, _ := ret[0].(uint64)
+	ret1, _ := ret[1].(byte)
+	ret2, _ := ret[2].(error)
+	return ret0, ret1, ret2
 }
 
-// Read indicates an expected call of Read
-func (mr *MockSegmentReaderMockRecorder) Read(arg0 interface{}) *gomock.Call {
+// Read64 indicates an expected call of Read64
+func (mr *MockSegmentReaderMockRecorder) Read64() *gomock.Call {
 	mr.mock.ctrl.T.Helper()
-	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "Read", reflect.TypeOf((*MockSegmentReader)(nil).Read), arg0)
+	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "Read64", reflect.TypeOf((*MockSegmentReader)(nil).Read64))
 }
 
 // Reset mocks base method
diff --git a/src/dbnode/x/xio/null.go b/src/dbnode/x/xio/null.go
index 81fdebad47..146b12519f 100644
--- a/src/dbnode/x/xio/null.go
+++ b/src/dbnode/x/xio/null.go
@@ -27,7 +27,8 @@ import (
 
 type nullSegmentReader struct{}
 
-func (r nullSegmentReader) Read(_ []byte) (n int, err error) { return 0, nil }
+func (r nullSegmentReader) Read64() (word uint64, n byte, err error) { return 0, 0, nil }
+func (r nullSegmentReader) Peek64() (word uint64, n byte, err error) { return 0, 0, nil }
 func (r nullSegmentReader) Segment() (ts.Segment, error)     { return ts.Segment{}, nil }
 func (r nullSegmentReader) Reset(_ ts.Segment)               {}
 func (r nullSegmentReader) Finalize()                        {}
diff --git a/src/dbnode/x/xio/reader64.go b/src/dbnode/x/xio/reader64.go
new file mode 100644
index 0000000000..37ccf7a404
--- /dev/null
+++ b/src/dbnode/x/xio/reader64.go
@@ -0,0 +1,86 @@
+// Copyright (c) 2020 Uber Technologies, Inc.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+
+package xio
+
+import (
+	"encoding/binary"
+	"io"
+)
+
+// BytesReader64 implements a Reader64 over a slice of bytes.
+type BytesReader64 struct {
+	data  []byte
+	index int
+}
+
+// NewBytesReader64 creates a new BytesReader64.
+func NewBytesReader64(data []byte) *BytesReader64 {
+	return &BytesReader64{data: data}
+}
+
+// Read64 reads and returns a 64 bit word plus a number of bytes (up to 8) actually read.
+func (r *BytesReader64) Read64() (word uint64, n byte, err error) {
+	if r.index+8 <= len(r.data) {
+		// NB: this compiles to a single 64 bit load followed by
+		// a BSWAPQ on amd64 gc 1.13 (https://godbolt.org/z/oTK1jx).
+		res := binary.BigEndian.Uint64(r.data[r.index:])
+		r.index += 8
+		return res, 8, nil
+	}
+	if r.index >= len(r.data) {
+		return 0, 0, io.EOF
+	}
+	var res uint64
+	var bytes byte
+	for ; r.index < len(r.data); r.index++ {
+		res = (res << 8) | uint64(r.data[r.index])
+		bytes++
+	}
+	return res << (64 - 8*bytes), bytes, nil
+}
+
+// Peek64 peeks and returns the next 64 bit word plus a number of bytes (up to 8) available.
+func (r *BytesReader64) Peek64() (word uint64, n byte, err error) {
+	if r.index+8 <= len(r.data) {
+		// NB: this compiles to a single 64 bit load followed by
+		// BSWAPQ on amd64 gc 1.13 (https://godbolt.org/z/oTK1jx).
+		res := binary.BigEndian.Uint64(r.data[r.index:])
+		return res, 8, nil
+	}
+
+	if r.index >= len(r.data) {
+		return 0, 0, io.EOF
+	}
+
+	var res uint64
+	var bytes byte
+	for i := r.index; i < len(r.data); i++ {
+		res = (res << 8) | uint64(r.data[i])
+		bytes++
+	}
+	return res << (64 - 8*bytes), bytes, nil
+}
+
+// Reset resets the BytesReader64 for reuse.
+func (r *BytesReader64) Reset(data []byte) {
+	r.data = data
+	r.index = 0
+}
diff --git a/src/dbnode/x/xio/reader64_test.go b/src/dbnode/x/xio/reader64_test.go
new file mode 100644
index 0000000000..98d29bdb11
--- /dev/null
+++ b/src/dbnode/x/xio/reader64_test.go
@@ -0,0 +1,74 @@
+// Copyright (c) 2020 Uber Technologies, Inc.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+
+package xio
+
+import (
+	"encoding/binary"
+	"io"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestBytesReader64(t *testing.T) {
+	var (
+		data = []byte{4, 5, 6, 7, 8, 9, 1, 2, 3, 0, 10, 11, 12, 13, 14, 15, 16, 17}
+		r    = NewBytesReader64(nil)
+	)
+
+	for l := 0; l < len(data); l++ {
+		testBytesReader64(t, r, data[:l])
+	}
+}
+
+func testBytesReader64(t *testing.T, r *BytesReader64, data []byte) {
+	r.Reset(data)
+
+	var (
+		peeked = []byte{}
+		read   = []byte{}
+		buf    [8]byte
+		word   uint64
+		n      byte
+		err    error
+	)
+
+	for {
+		word, n, err = r.Peek64()
+		if err != nil {
+			break
+		}
+		binary.BigEndian.PutUint64(buf[:], word)
+		peeked = append(peeked, buf[:n]...)
+
+		word, n, err = r.Read64()
+		if err != nil {
+			break
+		}
+		binary.BigEndian.PutUint64(buf[:], word)
+		read = append(read, buf[:n]...)
+	}
+
+	require.Equal(t, io.EOF, err)
+	assert.Equal(t, data, peeked)
+	assert.Equal(t, data, read)
+}
diff --git a/src/dbnode/x/xio/segment_reader.go b/src/dbnode/x/xio/segment_reader.go
index 352c8feeea..5555937cc2 100644
--- a/src/dbnode/x/xio/segment_reader.go
+++ b/src/dbnode/x/xio/segment_reader.go
@@ -21,6 +21,7 @@
 package xio
 
 import (
+	"encoding/binary"
 	"io"
 
 	"github.com/m3db/m3/src/dbnode/ts"
@@ -46,40 +47,103 @@ func (sr *segmentReader) Clone(
 	return NewSegmentReader(sr.segment.Clone(pool)), nil
 }
 
-func (sr *segmentReader) Read(b []byte) (int, error) {
-	if len(b) == 0 {
-		return 0, nil
+func (sr *segmentReader) Read64() (word uint64, n byte, err error) {
+	sr.lazyInit()
+
+	var (
+		headLen = len(sr.lazyHead)
+		res     uint64
+		bytes   byte
+	)
+
+	if sr.si+8 <= headLen {
+		// NB: this compiles to a single 64 bit load followed by
+		// a BSWAPQ on amd64 gc 1.13 (https://godbolt.org/z/oTK1jx).
+		res = binary.BigEndian.Uint64(sr.lazyHead[sr.si:])
+		sr.si += 8
+		return res, 8, nil
 	}
 
-	if b := sr.segment.Head; b != nil && len(sr.lazyHead) == 0 {
-		sr.lazyHead = b.Bytes()
+	headTailLen := headLen + len(sr.lazyTail)
+
+	if sr.si < headLen {
+		for ; sr.si < headLen; sr.si++ {
+			res = (res << 8) | uint64(sr.lazyHead[sr.si])
+			bytes++
+		}
+		for ; sr.si < headTailLen && bytes < 8; sr.si++ {
+			res = (res << 8) | uint64(sr.lazyTail[sr.si-headLen])
+			bytes++
+		}
+		return res << (64 - 8*bytes), bytes, nil
 	}
-	if b := sr.segment.Tail; b != nil && len(sr.lazyTail) == 0 {
-		sr.lazyTail = b.Bytes()
+
+	if sr.si+8 <= headTailLen {
+		// NB: this compiles to a single 64 bit load followed by
+		// a BSWAPQ on amd64 gc 1.13 (https://godbolt.org/z/oTK1jx).
+		res = binary.BigEndian.Uint64(sr.lazyTail[sr.si-headLen:])
+		sr.si += 8
+		return res, 8, nil
+	}
+
+	if sr.si >= headTailLen {
+		return 0, 0, io.EOF
 	}
 
-	nh, nt := len(sr.lazyHead), len(sr.lazyTail)
-	if sr.si >= nh+nt {
-		return 0, io.EOF
+	for ; sr.si < headTailLen; sr.si++ {
+		res = (res << 8) | uint64(sr.lazyTail[sr.si-headLen])
+		bytes++
+	}
+	return res << (64 - 8*bytes), bytes, nil
+}
+
+func (sr *segmentReader) Peek64() (word uint64, n byte, err error) {
+	sr.lazyInit()
+
+	var (
+		headLen = len(sr.lazyHead)
+		i       = sr.si
+		res     uint64
+		bytes   byte
+	)
+
+	if i+8 <= headLen {
+		// NB: this compiles to a single 64 bit load followed by
+		// a BSWAPQ on amd64 gc 1.13 (https://godbolt.org/z/oTK1jx).
+		res = binary.BigEndian.Uint64(sr.lazyHead[i:])
+		return res, 8, nil
 	}
-	n := 0
-	if sr.si < nh {
-		nRead := copy(b, sr.lazyHead[sr.si:])
-		sr.si += nRead
-		n += nRead
-		if n == len(b) {
-			return n, nil
+
+	headTailLen := headLen + len(sr.lazyTail)
+
+	if i < headLen {
+		for ; i < headLen; i++ {
+			res = (res << 8) | uint64(sr.lazyHead[i])
+			bytes++
+		}
+		for ; i < headTailLen && bytes < 8; i++ {
+			res = (res << 8) | uint64(sr.lazyTail[i-headLen])
+			bytes++
 		}
+		return res << (64 - 8*bytes), bytes, nil
 	}
-	if sr.si < nh+nt {
-		nRead := copy(b[n:], sr.lazyTail[sr.si-nh:])
-		sr.si += nRead
-		n += nRead
+
+	if i+8 <= headTailLen {
+		// NB: this compiles to a single 64 bit load followed by
+		// a BSWAPQ on amd64 gc 1.13 (https://godbolt.org/z/oTK1jx).
+		res = binary.BigEndian.Uint64(sr.lazyTail[i-headLen:])
+		return res, 8, nil
+	}
+
+	if i >= headTailLen {
+		return 0, 0, io.EOF
 	}
-	if n == 0 {
-		return 0, io.EOF
+
+	for ; i < headTailLen; i++ {
+		res = (res << 8) | uint64(sr.lazyTail[i-headLen])
+		bytes++
 	}
-	return n, nil
+	return res << (64 - 8*bytes), bytes, nil
 }
 
 func (sr *segmentReader) Segment() (ts.Segment, error) {
@@ -102,3 +166,12 @@ func (sr *segmentReader) Finalize() {
 		pool.Put(sr)
 	}
 }
+
+func (sr *segmentReader) lazyInit() {
+	if b := sr.segment.Head; b != nil && len(sr.lazyHead) == 0 {
+		sr.lazyHead = b.Bytes()
+	}
+	if b := sr.segment.Tail; b != nil && len(sr.lazyTail) == 0 {
+		sr.lazyTail = b.Bytes()
+	}
+}
diff --git a/src/dbnode/x/xio/segment_reader_test.go b/src/dbnode/x/xio/segment_reader_test.go
index ef0f704fb0..fed14e0680 100644
--- a/src/dbnode/x/xio/segment_reader_test.go
+++ b/src/dbnode/x/xio/segment_reader_test.go
@@ -21,6 +21,7 @@
 package xio
 
 import (
+	"encoding/binary"
 	"io"
 	"testing"
 
@@ -52,6 +53,10 @@ var (
 
 type byteFunc func(d []byte) checked.Bytes
 
+func checkedNoPool(d []byte) checked.Bytes {
+	return checked.NewBytes(d, nil)
+}
+
 func testSegmentReader(
 	t *testing.T,
 	checkd byteFunc,
@@ -60,15 +65,9 @@ func testSegmentReader(
 	checksum := uint32(10)
 	segment := ts.NewSegment(checkd(head), checkd(tail), checksum, ts.FinalizeNone)
 	r := NewSegmentReader(segment)
-	var b [100]byte
-	n, err := r.Read(b[:])
-	require.NoError(t, err)
-	require.Equal(t, len(expected), n)
-	require.Equal(t, expected, b[:n])
-
-	n, err = r.Read(b[:])
+	bytes, err := ToBytes(r)
 	require.Equal(t, io.EOF, err)
-	require.Equal(t, 0, n)
+	require.Equal(t, expected, bytes)
 
 	seg, err := r.Segment()
 	require.NoError(t, err)
@@ -92,13 +91,13 @@ func testSegmentReader(
 	cloned.Finalize()
 	segment.Finalize()
 }
+
 func TestSegmentReaderNoPool(t *testing.T) {
-	checkd := func(d []byte) checked.Bytes { return checked.NewBytes(d, nil) }
-	testSegmentReader(t, checkd, nil)
+	testSegmentReader(t, checkedNoPool, nil)
 }
 
 func TestSegmentReaderWithPool(t *testing.T) {
-	bytesPool := pool.NewCheckedBytesPool([]pool.Bucket{pool.Bucket{
+	bytesPool := pool.NewCheckedBytesPool([]pool.Bucket{{
 		Capacity: 1024,
 		Count:    10,
 	}}, nil, func(s []pool.Bucket) pool.BytesPool {
@@ -115,3 +114,54 @@ func TestSegmentReaderWithPool(t *testing.T) {
 
 	testSegmentReader(t, checkd, bytesPool)
 }
+
+func TestSegmentReader64(t *testing.T) {
+	data := make([]byte, 32)
+	for i := range data {
+		data[i] = 100 + byte(i)
+	}
+
+	for headLen := 0; headLen < len(data); headLen++ {
+		for tailLen := 0; tailLen < len(data)-headLen; tailLen++ {
+			testSegmentReader64(t, data[:headLen], data[headLen:headLen+tailLen])
+		}
+	}
+}
+
+func testSegmentReader64(t *testing.T, head []byte, tail []byte) {
+	var expected []byte
+	expected = append(expected, head...)
+	expected = append(expected, tail...)
+
+	var (
+		segment      = ts.NewSegment(checkedNoPool(head), checkedNoPool(tail), 0, ts.FinalizeNone)
+		r            = NewSegmentReader(segment)
+		peeked, read []byte
+		buf          [8]byte
+		word         uint64
+		n            byte
+		err          error
+	)
+
+	for {
+		word, n, err = r.Peek64()
+		if err != nil {
+			break
+		}
+		binary.BigEndian.PutUint64(buf[:], word)
+		peeked = append(peeked, buf[:n]...)
+
+		word, n, err = r.Read64()
+		require.NoError(t, err)
+
+		binary.BigEndian.PutUint64(buf[:], word)
+		read = append(read, buf[:n]...)
+	}
+
+	require.Equal(t, io.EOF, err)
+	require.Equal(t, expected, peeked)
+	require.Equal(t, expected, read)
+
+	_, _, err = r.Read64()
+	require.Equal(t, io.EOF, err)
+}
diff --git a/src/dbnode/x/xio/types.go b/src/dbnode/x/xio/types.go
index fd02692fed..28cd107f0c 100644
--- a/src/dbnode/x/xio/types.go
+++ b/src/dbnode/x/xio/types.go
@@ -21,7 +21,6 @@
 package xio
 
 import (
-	"io"
 	"time"
 
 	"github.com/m3db/m3/src/dbnode/ts"
@@ -42,7 +41,7 @@ var EmptyBlockReader = BlockReader{}
 
 // SegmentReader implements the io reader interface backed by a segment.
 type SegmentReader interface {
-	io.Reader
+	Reader64
 	xresource.Finalizer
 
 	// Segment gets the segment read by this reader.
@@ -103,3 +102,13 @@ type ReaderSliceOfSlicesFromBlockReadersIterator interface {
 	// Reset resets the iterator with a new array of block readers arrays.
 	Reset(blocks [][]BlockReader)
 }
+
+// Reader64 is a reader for reading 64 bit words.
+type Reader64 interface {
+
+	// Read64 reads and returns a 64 bit word plus a number of bytes (up to 8) actually read.
+	Read64() (word uint64, n byte, err error)
+
+	// Read64 peeks and returns the next 64 bit word plus a number of bytes (up to 8) available.
+	Peek64() (word uint64, n byte, err error)
+}
diff --git a/src/dbnode/x/xio/utils.go b/src/dbnode/x/xio/utils.go
new file mode 100644
index 0000000000..8374bc7af9
--- /dev/null
+++ b/src/dbnode/x/xio/utils.go
@@ -0,0 +1,40 @@
+// Copyright (c) 2020 Uber Technologies, Inc.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+
+package xio
+
+import "encoding/binary"
+
+// ToBytes reads and returns the contents of Reader64 as a slice of bytes.
+// Should normally return io.EOF as an error.
+func ToBytes(reader Reader64) ([]byte, error) {
+	var (
+		res []byte
+		buf [8]byte
+	)
+
+	word, bytes, err := reader.Read64()
+	for ; err == nil; word, bytes, err = reader.Read64() {
+		binary.BigEndian.PutUint64(buf[:], word)
+		res = append(res, buf[:bytes]...)
+	}
+
+	return res, err
+}
diff --git a/src/query/pools/query_pools.go b/src/query/pools/query_pools.go
index 65c5c7ad99..d0e1dcd360 100644
--- a/src/query/pools/query_pools.go
+++ b/src/query/pools/query_pools.go
@@ -21,11 +21,10 @@
 package pools
 
 import (
-	"io"
-
 	"github.com/m3db/m3/src/dbnode/encoding"
 	"github.com/m3db/m3/src/dbnode/encoding/m3tsz"
 	"github.com/m3db/m3/src/dbnode/namespace"
+	"github.com/m3db/m3/src/dbnode/x/xio"
 	"github.com/m3db/m3/src/dbnode/x/xpool"
 	xconfig "github.com/m3db/m3/src/x/config"
 	"github.com/m3db/m3/src/x/ident"
@@ -42,10 +41,8 @@ const (
 	defaultReplicas                    = 3
 	defaultSeriesIteratorPoolSize      = 2 << 12 // ~8k
 	defaultCheckedBytesWrapperPoolSize = 2 << 12 // ~8k
-	defaultBucketCapacity              = 256
 	defaultPoolableConcurrentQueries   = 64
 	defaultPoolableSeriesPerQuery      = 4096
-	defaultSeriesReplicaReaderPoolSize = defaultPoolableConcurrentQueries * defaultPoolableSeriesPerQuery * defaultReplicas
 )
 
 var (
@@ -212,16 +209,15 @@ func BuildIteratorPools(
 	encodingOpts := encoding.NewOptions().
 		SetReaderIteratorPool(readerIteratorPool)
 
-	readerIteratorPool.Init(func(r io.Reader, descr namespace.SchemaDescr) encoding.ReaderIterator {
-		return m3tsz.NewReaderIterator(r, m3tsz.DefaultIntOptimizationEnabled, encodingOpts)
-	})
+	readerIteratorPool.Init(m3tsz.DefaultReaderIteratorAllocFn(encodingOpts))
 
 	pools.multiReaderIterator = encoding.NewMultiReaderIteratorPool(defaultPerSeriesPoolOpts)
-	pools.multiReaderIterator.Init(func(r io.Reader, s namespace.SchemaDescr) encoding.ReaderIterator {
-		iter := readerIteratorPool.Get()
-		iter.Reset(r, s)
-		return iter
-	})
+	pools.multiReaderIterator.Init(
+		func(r xio.Reader64, s namespace.SchemaDescr) encoding.ReaderIterator {
+			iter := readerIteratorPool.Get()
+			iter.Reset(r, s)
+			return iter
+		})
 
 	pools.seriesIterator = encoding.NewSeriesIteratorPool(defaultPerSeriesPoolOpts)
 	pools.seriesIterator.Init()
diff --git a/src/query/remote/compressed_codecs.go b/src/query/remote/compressed_codecs.go
index 166cefcd2c..77f41772a6 100644
--- a/src/query/remote/compressed_codecs.go
+++ b/src/query/remote/compressed_codecs.go
@@ -22,7 +22,6 @@ package remote
 
 import (
 	"fmt"
-	"io"
 	"sync"
 	"time"
 
@@ -47,14 +46,12 @@ func initializeVars() {
 			b.Reset(nil)
 		}))
 
-	iterAlloc = func(r io.Reader, _ namespace.SchemaDescr) encoding.ReaderIterator {
-		return m3tsz.NewReaderIterator(r, m3tsz.DefaultIntOptimizationEnabled, encoding.NewOptions())
-	}
+	iterAlloc = m3tsz.DefaultReaderIteratorAllocFn(encoding.NewOptions())
 }
 
 var (
 	opts       checked.BytesOptions
-	iterAlloc  func(r io.Reader, d namespace.SchemaDescr) encoding.ReaderIterator
+	iterAlloc  func(r xio.Reader64, d namespace.SchemaDescr) encoding.ReaderIterator
 	initialize sync.Once
 )
 
diff --git a/src/query/test/test_series_iterator.go b/src/query/test/test_series_iterator.go
index a2adb81b66..26b1586fe8 100644
--- a/src/query/test/test_series_iterator.go
+++ b/src/query/test/test_series_iterator.go
@@ -22,7 +22,6 @@ package test
 
 import (
 	"fmt"
-	"io"
 	"sort"
 	"time"
 
@@ -53,7 +52,7 @@ var (
 	// End is the expected end time for the generated series
 	End time.Time
 
-	testIterAlloc func(r io.Reader, d namespace.SchemaDescr) encoding.ReaderIterator
+	testIterAlloc func(r xio.Reader64, d namespace.SchemaDescr) encoding.ReaderIterator
 )
 
 func init() {
@@ -68,9 +67,7 @@ func init() {
 	Middle = Start.Add(BlockSize)
 	End = Middle.Add(BlockSize)
 
-	testIterAlloc = func(r io.Reader, _ namespace.SchemaDescr) encoding.ReaderIterator {
-		return m3tsz.NewReaderIterator(r, m3tsz.DefaultIntOptimizationEnabled, encoding.NewOptions())
-	}
+	testIterAlloc = m3tsz.DefaultReaderIteratorAllocFn(encoding.NewOptions())
 }
 
 // Builds a MultiReaderIterator representing a single replica
diff --git a/src/query/ts/m3db/encoded_step_iterator_test.go b/src/query/ts/m3db/encoded_step_iterator_test.go
index 6b9a91f690..85b5ad166e 100644
--- a/src/query/ts/m3db/encoded_step_iterator_test.go
+++ b/src/query/ts/m3db/encoded_step_iterator_test.go
@@ -22,7 +22,6 @@ package m3db
 
 import (
 	"fmt"
-	"io"
 	"os"
 	"runtime"
 	"sync"
@@ -44,8 +43,8 @@ import (
 	"github.com/m3db/m3/src/x/pool"
 	xsync "github.com/m3db/m3/src/x/sync"
 	xtime "github.com/m3db/m3/src/x/time"
-	"github.com/pkg/profile"
 
+	"github.com/pkg/profile"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
@@ -478,7 +477,7 @@ func setupBlock(b *testing.B, iterations int, t iterType) (block.Block, reset, s
 				m3tsz.DefaultIntOptimizationEnabled, encodingOpts)
 
 			iterAlloc := func(
-				r io.Reader,
+				r xio.Reader64,
 				d namespace.SchemaDescr,
 			) encoding.ReaderIterator {
 				readerIter.Reset(r, d)
diff --git a/src/query/ts/m3db/options.go b/src/query/ts/m3db/options.go
index 43867c654e..153df2aac7 100644
--- a/src/query/ts/m3db/options.go
+++ b/src/query/ts/m3db/options.go
@@ -23,13 +23,11 @@ package m3db
 import (
 	"errors"
 	"fmt"
-	"io"
 	"time"
 
 	"github.com/m3db/m3/src/dbnode/client"
 	"github.com/m3db/m3/src/dbnode/encoding"
 	"github.com/m3db/m3/src/dbnode/encoding/m3tsz"
-	"github.com/m3db/m3/src/dbnode/namespace"
 	"github.com/m3db/m3/src/query/models"
 	"github.com/m3db/m3/src/query/pools"
 	queryconsolidator "github.com/m3db/m3/src/query/storage/m3/consolidators"
@@ -39,13 +37,11 @@ import (
 )
 
 var (
-	defaultCapacity         = 1024
-	defaultCount            = 10
-	defaultLookbackDuration = time.Duration(0)
-	defaultConsolidationFn  = consolidators.TakeLast
-	defaultIterAlloc        = func(r io.Reader, _ namespace.SchemaDescr) encoding.ReaderIterator {
-		return m3tsz.NewReaderIterator(r, m3tsz.DefaultIntOptimizationEnabled, encoding.NewOptions())
-	}
+	defaultCapacity             = 1024
+	defaultCount                = 10
+	defaultLookbackDuration     = time.Duration(0)
+	defaultConsolidationFn      = consolidators.TakeLast
+	defaultIterAlloc            = m3tsz.DefaultReaderIteratorAllocFn(encoding.NewOptions())
 	defaultIteratorBatchingFn   = iteratorBatchingFn
 	defaultBlockSeriesProcessor = NewBlockSeriesProcessor()
 	defaultInstrumented         = true