Close iterator properly and check nil before releasing buffers.

pkg/chunkenc/memchunk.go

@@ -695,16 +695,21 @@ func (si *bufferedIterator) close() {
 		current.BytesDecompressed += si.bytesDecompressed
 		current.BytesCompressed += int64(len(si.origBytes))
 	})
-	si.pool.PutReader(si.reader)
-	BufReaderPool.Put(si.bufReader)
+	if si.reader != nil {
+		si.pool.PutReader(si.reader)
+		si.reader = nil
+	}
+	if si.bufReader != nil {
+		BufReaderPool.Put(si.bufReader)
+		si.bufReader = nil
+	}
+
 	if si.buf != nil {
 		BytesBufferPool.Put(si.buf)
+		si.buf = nil
 	}
 	si.origBytes = nil
-	si.bufReader = nil
-	si.buf = nil
 	si.decBuf = nil
-	si.reader = nil
 }
 
 func (si *bufferedIterator) Labels() string { return "" }

pkg/chunkenc/memchunk_test.go

@@ -13,6 +13,7 @@ import (
 
 	"github.com/dustin/go-humanize"
 	"github.com/grafana/loki/pkg/chunkenc/testdata"
+	"github.com/grafana/loki/pkg/iter"
 	"github.com/grafana/loki/pkg/logproto"
 	"github.com/stretchr/testify/require"
 )
@@ -394,6 +395,47 @@ func TestChunkSize(t *testing.T) {
 	}
 }
 
+func TestIteratorClose(t *testing.T) {
+	for _, enc := range testEncoding {
+		t.Run(enc.String(), func(t *testing.T) {
+			for _, test := range []func(iter iter.EntryIterator, t *testing.T){
+				func(iter iter.EntryIterator, t *testing.T) {
+					// close without iterating
+					if err := iter.Close(); err != nil {
+						t.Fatal(err)
+					}
+				},
+				func(iter iter.EntryIterator, t *testing.T) {
+					// close after iterating
+					for iter.Next() {
+						_ = iter.Entry()
+					}
+					if err := iter.Close(); err != nil {
+						t.Fatal(err)
+					}
+				},
+				func(iter iter.EntryIterator, t *testing.T) {
+					// close after a single iteration
+					iter.Next()
+					_ = iter.Entry()
+					if err := iter.Close(); err != nil {
+						t.Fatal(err)
+					}
+				},
+			} {
+				c := NewMemChunk(enc)
+				inserted := fillChunk(c)
+				iter, err := c.Iterator(context.Background(), time.Unix(0, 0), time.Unix(0, inserted), logproto.BACKWARD, nil)
+				if err != nil {
+					t.Fatal(err)
+				}
+				test(iter, t)
+			}
+
+		})
+	}
+}
+
 var result []Chunk
 
 func BenchmarkWrite(b *testing.B) {

pkg/iter/iterator.go

@@ -522,7 +522,12 @@ func (i *entryIteratorBackward) Entry() logproto.Entry {
 	return i.cur
 }
 
-func (i *entryIteratorBackward) Close() error { return nil }
+func (i *entryIteratorBackward) Close() error {
+	if !i.loaded {
+		return i.forwardIter.Close()
+	}
+	return nil
+}
 
 func (i *entryIteratorBackward) Error() error { return nil }
 
@@ -608,7 +613,12 @@ func (i *entryIteratorForward) Entry() logproto.Entry {
 	return i.cur.entry
 }
 
-func (i *entryIteratorForward) Close() error { return nil }
+func (i *entryIteratorForward) Close() error {
+	if !i.loaded {
+		return i.backwardIter.Close()
+	}
+	return nil
+}
 
 func (i *entryIteratorForward) Error() error { return nil }