From dd43210b45451ad3089a94e5c437884416741a2d Mon Sep 17 00:00:00 2001 From: Roy Crihfield Date: Thu, 22 Jul 2021 18:12:20 +0800 Subject: [PATCH 1/8] Implement BadgerDB backend --- db/badgerdb/db.go | 402 +++++++++++++++++++++++++++++++++++++++++ db/badgerdb/db_test.go | 36 ++++ 2 files changed, 438 insertions(+) create mode 100644 db/badgerdb/db.go create mode 100644 db/badgerdb/db_test.go diff --git a/db/badgerdb/db.go b/db/badgerdb/db.go new file mode 100644 index 000000000000..c362eb74eeb7 --- /dev/null +++ b/db/badgerdb/db.go @@ -0,0 +1,402 @@ +package badgerdb + +import ( + "bytes" + "encoding/csv" + "math" + "os" + "path/filepath" + "strconv" + "sync" + "sync/atomic" + + dbm "github.com/cosmos/cosmos-sdk/db" + + "github.com/dgraph-io/badger/v3" +) + +var ( + versionsFilename string = "versions.csv" +) + +var _ dbm.DBConnection = (*BadgerDB)(nil) +var _ dbm.DBReader = (*badgerTxn)(nil) +var _ dbm.DBWriter = (*badgerWriter)(nil) +var _ dbm.DBReadWriter = (*badgerWriter)(nil) + +// BadgerDB is a connection to a BadgerDB key-value database. +type BadgerDB struct { + db *badger.DB + vmgr *versionManager + mtx sync.RWMutex + // Track open DBWriters + openWriters int32 +} + +type badgerTxn struct { + txn *badger.Txn + // vmgr *versionManager + db *BadgerDB +} +type badgerWriter struct { + badgerTxn +} + +type badgerIterator struct { + reverse bool + start, end []byte + iter *badger.Iterator + lastErr error + primed bool +} + +// Map our versions to Badger timestamps. +// +// A badger Txn's commit TS must be strictly greater than a record's "last-read" +// TS in order to detect conflicts, and a Txn must be read at a TS after last +// commit to see current state. So we must use commit increments that are more +// granular than a version interval, mapping latter -> former. +type versionManager struct { + *dbm.VersionManager + vmap versionTsMap + lastTs uint64 +} +type versionTsMap map[uint64]uint64 + +// NewDB creates or loads a BadgerDB key-value database inside the given directory. +// If dir does not exist, it will be created. +func NewDB(dir string) (*BadgerDB, error) { + // Since Badger doesn't support database names, we join both to obtain + // the final directory to use for the database. + if err := os.MkdirAll(dir, 0755); err != nil { + return nil, err + } + opts := badger.DefaultOptions(dir) + // todo: NumVersionsToKeep + opts.SyncWrites = false // note that we have Sync methods + opts.Logger = nil // badger is too chatty by default + return NewDBWithOptions(opts) +} + +// NewDBWithOptions creates a BadgerDB key-value database with the specified Options +// (https://pkg.go.dev/github.com/dgraph-io/badger/v3#Options) +func NewDBWithOptions(opts badger.Options) (*BadgerDB, error) { + db, err := badger.OpenManaged(opts) + if err != nil { + return nil, err + } + vmgr, err := readVersionsFile(filepath.Join(opts.Dir, versionsFilename)) + if err != nil { + return nil, err + } + return &BadgerDB{ + db: db, + vmgr: vmgr, + }, nil +} + +// Load metadata CSV file containing valid versions +func readVersionsFile(path string) (*versionManager, error) { + file, err := os.OpenFile(path, os.O_RDONLY|os.O_CREATE, 0644) + if err != nil { + return nil, err + } + defer file.Close() + r := csv.NewReader(file) + r.FieldsPerRecord = 2 + rows, err := r.ReadAll() + if err != nil { + return nil, err + } + var versions []uint64 + var ts uint64 + vmap := make(versionTsMap) + for _, row := range rows { + version, err := strconv.ParseUint(row[0], 10, 64) + if err != nil { + return nil, err + } + ts, err = strconv.ParseUint(row[1], 10, 64) + if err != nil { + return nil, err + } + versions = append(versions, version) + vmap[version] = ts + } + if ts == 0 { + ts = 1 + } + return &versionManager{dbm.NewVersionManager(versions), vmap, ts}, nil +} + +// Write version metadata to CSV file +func writeVersionsFile(vm *versionManager, path string) error { + file, err := os.OpenFile(path, os.O_WRONLY|os.O_CREATE, 0644) + if err != nil { + return err + } + defer file.Close() + w := csv.NewWriter(file) + var rows [][]string + for it := vm.Iterator(); it.Next(); { + version := it.Value() + ts, ok := vm.vmap[version] + if !ok { + panic("version not mapped to ts") + } + rows = append(rows, []string{ + strconv.FormatUint(it.Value(), 10), + strconv.FormatUint(ts, 10), + }) + } + return w.WriteAll(rows) +} + +func (b *BadgerDB) Reader() dbm.DBReader { + return &badgerTxn{txn: b.db.NewTransactionAt(math.MaxUint64, false), db: b} +} + +func (b *BadgerDB) ReaderAt(version uint64) (dbm.DBReader, error) { + b.mtx.RLock() + defer b.mtx.RUnlock() + if !b.vmgr.Exists(version) { + return nil, dbm.ErrVersionDoesNotExist + } + return &badgerTxn{txn: b.db.NewTransactionAt(b.vmgr.versionTs(version), false), db: b}, nil +} + +func (b *BadgerDB) ReadWriter() dbm.DBReadWriter { + atomic.AddInt32(&b.openWriters, 1) + b.mtx.RLock() + ts := b.vmgr.lastCommitTs() + b.mtx.RUnlock() + return &badgerWriter{badgerTxn{txn: b.db.NewTransactionAt(ts, true), db: b}} +} + +func (b *BadgerDB) Writer() dbm.DBWriter { + // Badger has a WriteBatch, but it doesn't support conflict detection + return b.ReadWriter() +} + +func (b *BadgerDB) Close() error { + b.mtx.Lock() + defer b.mtx.Unlock() + writeVersionsFile(b.vmgr, filepath.Join(b.db.Opts().Dir, versionsFilename)) + return b.db.Close() +} + +// Versions implements DBConnection. +// Returns a VersionSet that is valid until the next call to SaveVersion or DeleteVersion. +func (b *BadgerDB) Versions() (dbm.VersionSet, error) { + b.mtx.RLock() + defer b.mtx.RUnlock() + return b.vmgr, nil +} + +func (b *BadgerDB) save(target uint64) (uint64, error) { + b.mtx.Lock() + defer b.mtx.Unlock() + if b.openWriters > 0 { + return 0, dbm.ErrOpenTransactions + } + b.vmgr = b.vmgr.Copy() + return b.vmgr.Save(target) +} + +// SaveVersion implements DBConnection. +func (b *BadgerDB) SaveNextVersion() (uint64, error) { + return b.save(0) +} + +// SaveNextVersion implements DBConnection. +func (b *BadgerDB) SaveVersion(target uint64) error { + if target == 0 { + return dbm.ErrInvalidVersion + } + _, err := b.save(target) + return err +} + +func (b *BadgerDB) DeleteVersion(target uint64) error { + b.mtx.Lock() + defer b.mtx.Unlock() + if !b.vmgr.Exists(target) { + return dbm.ErrVersionDoesNotExist + } + b.vmgr = b.vmgr.Copy() + b.vmgr.Delete(target) + return nil +} + +func (b *BadgerDB) Stats() map[string]string { return nil } + +func (tx *badgerTxn) Get(key []byte) ([]byte, error) { + if len(key) == 0 { + return nil, dbm.ErrKeyEmpty + } + + item, err := tx.txn.Get(key) + if err == badger.ErrKeyNotFound { + return nil, nil + } else if err != nil { + return nil, err + } + val, err := item.ValueCopy(nil) + if err == nil && val == nil { + val = []byte{} + } + return val, err +} + +func (tx *badgerTxn) Has(key []byte) (bool, error) { + if len(key) == 0 { + return false, dbm.ErrKeyEmpty + } + + _, err := tx.txn.Get(key) + if err != nil && err != badger.ErrKeyNotFound { + return false, err + } + return (err != badger.ErrKeyNotFound), nil +} + +func (tx *badgerWriter) Set(key, value []byte) error { + if len(key) == 0 { + return dbm.ErrKeyEmpty + } + if value == nil { + return dbm.ErrValueNil + } + return tx.txn.Set(key, value) +} + +func (tx *badgerWriter) Delete(key []byte) error { + if len(key) == 0 { + return dbm.ErrKeyEmpty + } + return tx.txn.Delete(key) +} + +func (tx *badgerWriter) Commit() error { + // Commit to the current commit TS, after ensuring it is > ReadTs + tx.db.vmgr.updateCommitTs(tx.txn.ReadTs()) + defer tx.Discard() + return tx.txn.CommitAt(tx.db.vmgr.lastCommitTs(), nil) +} + +func (tx *badgerTxn) Discard() { + tx.txn.Discard() +} + +func (tx *badgerWriter) Discard() { + defer atomic.AddInt32(&tx.db.openWriters, -1) + tx.badgerTxn.Discard() +} + +func (tx *badgerTxn) iteratorOpts(start, end []byte, opts badger.IteratorOptions) (*badgerIterator, error) { + if (start != nil && len(start) == 0) || (end != nil && len(end) == 0) { + return nil, dbm.ErrKeyEmpty + } + iter := tx.txn.NewIterator(opts) + iter.Rewind() + iter.Seek(start) + if opts.Reverse && iter.Valid() && bytes.Equal(iter.Item().Key(), start) { + // If we're going in reverse, our starting point was "end", which is exclusive. + iter.Next() + } + return &badgerIterator{ + reverse: opts.Reverse, + start: start, + end: end, + iter: iter, + primed: false, + }, nil +} + +func (tx *badgerTxn) Iterator(start, end []byte) (dbm.Iterator, error) { + opts := badger.DefaultIteratorOptions + return tx.iteratorOpts(start, end, opts) +} + +func (tx *badgerTxn) ReverseIterator(start, end []byte) (dbm.Iterator, error) { + opts := badger.DefaultIteratorOptions + opts.Reverse = true + return tx.iteratorOpts(end, start, opts) +} + +func (i *badgerIterator) Close() error { + i.iter.Close() + return nil +} + +func (i *badgerIterator) Domain() (start, end []byte) { return i.start, i.end } +func (i *badgerIterator) Error() error { return i.lastErr } + +func (i *badgerIterator) Next() bool { + if !i.primed { + i.primed = true + } else { + i.iter.Next() + } + return i.Valid() +} + +func (i *badgerIterator) Valid() bool { + if !i.iter.Valid() { + return false + } + if len(i.end) > 0 { + key := i.iter.Item().Key() + if c := bytes.Compare(key, i.end); (!i.reverse && c >= 0) || (i.reverse && c < 0) { + // We're at the end key, or past the end. + return false + } + } + return true +} + +func (i *badgerIterator) Key() []byte { + if !i.Valid() { + panic("iterator is invalid") + } + return i.iter.Item().KeyCopy(nil) +} + +func (i *badgerIterator) Value() []byte { + if !i.Valid() { + panic("iterator is invalid") + } + val, err := i.iter.Item().ValueCopy(nil) + if err != nil { + i.lastErr = err + } + return val +} + +func (vm *versionManager) versionTs(ver uint64) uint64 { + return vm.vmap[ver] +} +func (vm *versionManager) lastCommitTs() uint64 { + return atomic.LoadUint64(&vm.lastTs) +} +func (vm *versionManager) Copy() *versionManager { + return &versionManager{ + VersionManager: vm.VersionManager.Copy(), + vmap: vm.vmap, + lastTs: vm.lastTs, + } +} + +// updateCommitTs atomically increments the lastTs if equal to readts. +// Returns the new value. +func (vm *versionManager) updateCommitTs(readts uint64) { + atomic.CompareAndSwapUint64(&vm.lastTs, readts, readts+1) +} +func (vm *versionManager) Save(target uint64) (uint64, error) { + id, err := vm.VersionManager.Save(target) + if err != nil { + return 0, err + } + vm.vmap[id] = atomic.LoadUint64(&vm.lastTs) + return id, nil +} diff --git a/db/badgerdb/db_test.go b/db/badgerdb/db_test.go new file mode 100644 index 000000000000..d451a63f4334 --- /dev/null +++ b/db/badgerdb/db_test.go @@ -0,0 +1,36 @@ +package badgerdb + +import ( + "testing" + + "github.com/stretchr/testify/require" + + dbm "github.com/cosmos/cosmos-sdk/db" + "github.com/cosmos/cosmos-sdk/db/dbtest" +) + +func load(t *testing.T, dir string) dbm.DBConnection { + db, err := NewDB(dir) + require.NoError(t, err) + return db +} + +func TestGetSetHasDelete(t *testing.T) { + dbtest.DoTestGetSetHasDelete(t, load) +} + +func TestIterators(t *testing.T) { + dbtest.DoTestIterators(t, load) +} + +func TestTransactions(t *testing.T) { + dbtest.DoTestTransactions(t, load, true) +} + +func TestVersioning(t *testing.T) { + dbtest.DoTestVersioning(t, load) +} + +func TestReloadDB(t *testing.T) { + dbtest.DoTestReloadDB(t, load) +} From ee9ae6e066550d8e7da451e954b5032ccb6d2f2c Mon Sep 17 00:00:00 2001 From: Roy Crihfield Date: Mon, 23 Aug 2021 12:39:49 +0800 Subject: [PATCH 2/8] update go.mod --- db/go.mod | 1 + db/go.sum | 135 +++++++++++++++++++++++++++++++++++++++++++++++++++++- 2 files changed, 134 insertions(+), 2 deletions(-) diff --git a/db/go.mod b/db/go.mod index 0d75f20d239b..c06b81730f12 100644 --- a/db/go.mod +++ b/db/go.mod @@ -3,6 +3,7 @@ go 1.15 module github.com/cosmos/cosmos-sdk/db require ( + github.com/dgraph-io/badger/v3 v3.2103.1 github.com/google/btree v1.0.0 github.com/stretchr/testify v1.7.0 ) diff --git a/db/go.sum b/db/go.sum index c7801a435648..5033ed4839c9 100644 --- a/db/go.sum +++ b/db/go.sum @@ -1,13 +1,144 @@ -github.com/davecgh/go-spew v1.1.0 h1:ZDRjVQ15GmhC3fiQ8ni8+OwkZQO4DARzQgrnXU1Liz8= +cloud.google.com/go v0.26.0/go.mod h1:aQUYkXzVsufM+DwF1aE+0xfcU+56JwCaLick0ClmMTw= +github.com/BurntSushi/toml v0.3.1/go.mod h1:xHWCNGjB5oqiDr8zfno3MHue2Ht5sIBksp03qcyfWMU= +github.com/OneOfOne/xxhash v1.2.2 h1:KMrpdQIwFcEqXDklaen+P1axHaj9BSKzvpUUfnHldSE= +github.com/OneOfOne/xxhash v1.2.2/go.mod h1:HSdplMjZKSmBqAxg5vPj2TmRDmfkzw+cTzAElWljhcU= +github.com/armon/consul-api v0.0.0-20180202201655-eb2c6b5be1b6/go.mod h1:grANhF5doyWs3UAsr3K4I6qtAmlQcZDesFNEHPZAzj8= +github.com/cespare/xxhash v1.1.0 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00:00:00 2001 From: Roy Crihfield Date: Mon, 23 Aug 2021 12:59:24 +0800 Subject: [PATCH 3/8] add badger to db/readme --- db/README.md | 25 +++++++++++++++++++++++++ 1 file changed, 25 insertions(+) diff --git a/db/README.md b/db/README.md index 2fda2a85b0c5..d40862ef79b5 100644 --- a/db/README.md +++ b/db/README.md @@ -37,3 +37,28 @@ This represents a self-contained and immutable view of a database's version hist The in-memory DB in the `db/memdb` package cannot be persisted to disk. It is implemented using the Google [btree](https://pkg.go.dev/github.com/google/btree) library. * This currently does not perform write conflict detection, so it only supports a single open write-transaction at a time. Multiple and concurrent read-transactions are supported. + +### BadgerDB ### + +A [BadgerDB](https://pkg.go.dev/github.com/dgraph-io/badger/v3)-based backend. Internally, this uses BadgerDB's "managed" mode for version management. +Note that Badger only recognizes write conflicts for rows that are read _after_ a conflicting transaction was opened. In other words, the following will raise an error: + +```go +tx1, tx2 := db.Writer(), db.ReadWriter() +key := []byte("key") +tx2.Get(key) +tx1.Set(key, []byte("a")) +tx2.Set(key, []byte("b")) +tx1.Commit() // ok +err := tx2.Commit() // err is non-nil +``` + +But this will not: +```go +tx1, tx2 := db.Writer(), db.ReadWriter() +key := []byte("key") +tx1.Set(key, []byte("a")) +tx2.Set(key, []byte("b")) +tx1.Commit() // ok +tx2.Commit() // ok +``` From 6304cc9ef763fcfcabc3a0523e0d090ee26f44aa Mon Sep 17 00:00:00 2001 From: Roy Crihfield Date: Mon, 23 Aug 2021 15:13:51 +0800 Subject: [PATCH 4/8] changelog entry --- CHANGELOG.md | 1 + 1 file changed, 1 insertion(+) diff --git a/CHANGELOG.md b/CHANGELOG.md index 0fb74788aaca..36b7924f8cd4 100644 --- a/CHANGELOG.md +++ b/CHANGELOG.md @@ -140,6 +140,7 @@ Ref: https://keepachangelog.com/en/1.0.0/ * [\#8518](https://github.com/cosmos/cosmos-sdk/pull/8518) Help users of multisig wallets debug signature issues. * [\#9573](https://github.com/cosmos/cosmos-sdk/pull/9573) ADR 040 implementation: New DB interface * [\#9952](https://github.com/cosmos/cosmos-sdk/pull/9952) ADR 040: Implement in-memory DB backend +* [\#9848](https://github.com/cosmos/cosmos-sdk/pull/9848) ADR-040: Implement BadgerDB backend ### Client Breaking Changes From 3fd1c6293180e9ea8cb4e6a8be5ed4c1959951ed Mon Sep 17 00:00:00 2001 From: Roy Crihfield Date: Fri, 10 Sep 2021 19:47:50 +0800 Subject: [PATCH 5/8] Apply suggestions from code review Co-authored-by: Aleksandr Bezobchuk --- db/badgerdb/db.go | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/db/badgerdb/db.go b/db/badgerdb/db.go index c362eb74eeb7..2a4cedc48378 100644 --- a/db/badgerdb/db.go +++ b/db/badgerdb/db.go @@ -29,7 +29,6 @@ type BadgerDB struct { db *badger.DB vmgr *versionManager mtx sync.RWMutex - // Track open DBWriters openWriters int32 } @@ -38,6 +37,7 @@ type badgerTxn struct { // vmgr *versionManager db *BadgerDB } + type badgerWriter struct { badgerTxn } @@ -61,6 +61,7 @@ type versionManager struct { vmap versionTsMap lastTs uint64 } + type versionTsMap map[uint64]uint64 // NewDB creates or loads a BadgerDB key-value database inside the given directory. From aa7a6e844cac7bf70267724ed42634e94da9736a Mon Sep 17 00:00:00 2001 From: Roy Crihfield Date: Fri, 10 Sep 2021 19:40:31 +0800 Subject: [PATCH 6/8] version manager should not require ordered slice in ctor --- db/version_manager.go | 14 +++++++++----- 1 file changed, 9 insertions(+), 5 deletions(-) diff --git a/db/version_manager.go b/db/version_manager.go index 55d88e97a2f1..1c04d2297ee8 100644 --- a/db/version_manager.go +++ b/db/version_manager.go @@ -2,6 +2,7 @@ package db import ( "fmt" + "math" ) // VersionManager encapsulates the current valid versions of a DB and computes @@ -13,16 +14,19 @@ type VersionManager struct { var _ VersionSet = (*VersionManager)(nil) -// NewVersionManager creates a VersionManager from a sorted slice of ascending version ids. +// NewVersionManager creates a VersionManager from a slice of version ids. func NewVersionManager(versions []uint64) *VersionManager { vmap := make(map[uint64]struct{}) var init, last uint64 + init = math.MaxUint64 for _, ver := range versions { vmap[ver] = struct{}{} - } - if len(versions) > 0 { - init = versions[0] - last = versions[len(versions)-1] + if ver < init { + init = ver + } + if ver > last { + last = ver + } } return &VersionManager{versions: vmap, initial: init, last: last} } From 88d7c449220878af83e6a508cef233b806b3fed9 Mon Sep 17 00:00:00 2001 From: Roy Crihfield Date: Fri, 10 Sep 2021 19:41:13 +0800 Subject: [PATCH 7/8] rewrite DoTestReloadDB save more versions, fewer values --- db/dbtest/testcases.go | 67 ++++++++++++++++++++++++------------------ 1 file changed, 38 insertions(+), 29 deletions(-) diff --git a/db/dbtest/testcases.go b/db/dbtest/testcases.go index 475950111d83..dedd0409229e 100644 --- a/db/dbtest/testcases.go +++ b/db/dbtest/testcases.go @@ -369,16 +369,19 @@ func DoTestReloadDB(t *testing.T, load Loader) { dirname := t.TempDir() db := load(t, dirname) - txn := db.Writer() - for i := 0; i < 100; i++ { + var firstVersions []uint64 + + for i := 0; i < 10; i++ { + txn := db.Writer() require.NoError(t, txn.Set(ikey(i), ival(i))) + require.NoError(t, txn.Commit()) + ver, err := db.SaveNextVersion() + require.NoError(t, err) + firstVersions = append(firstVersions, ver) } - require.NoError(t, txn.Commit()) - first, err := db.SaveNextVersion() - require.NoError(t, err) - txn = db.Writer() - for i := 0; i < 50; i++ { // overwrite some values + txn := db.Writer() + for i := 0; i < 5; i++ { // overwrite some values require.NoError(t, txn.Set(ikey(i), ival(i*10))) } require.NoError(t, txn.Commit()) @@ -386,45 +389,51 @@ func DoTestReloadDB(t *testing.T, load Loader) { require.NoError(t, err) txn = db.Writer() - for i := 100; i < 150; i++ { - require.NoError(t, txn.Set(ikey(i), ival(i))) - } + require.NoError(t, txn.Set(ikey(100), ival(100))) require.NoError(t, txn.Commit()) - db.Close() // Reload and check each saved version + db.Close() db = load(t, dirname) - view, err := db.ReaderAt(first) + // require.True(t, db.Versions().Equal(versions)) + vset, err := db.Versions() require.NoError(t, err) - for i := 0; i < 100; i++ { - v, err := view.Get(ikey(i)) - require.NoError(t, err) - require.Equal(t, ival(i), v) + require.Equal(t, last, vset.Last()) + + txn = db.Writer() + for i := 10; i < 15; i++ { + require.NoError(t, txn.Set(ikey(i), ival(i+10))) } - view.Discard() + require.NoError(t, txn.Commit()) - view, err = db.ReaderAt(last) - require.NoError(t, err) - for i := 0; i < 50; i++ { - v, err := view.Get(ikey(i)) + for i := 0; i < 10; i++ { + view, err := db.ReaderAt(firstVersions[i]) require.NoError(t, err) - require.Equal(t, ival(i*10), v) + val, err := view.Get(ikey(i)) + require.NoError(t, err) + require.Equal(t, ival(i), val) + view.Discard() } - for i := 50; i < 100; i++ { + + view, err := db.ReaderAt(last) + require.NoError(t, err) + for i := 0; i < 10; i++ { v, err := view.Get(ikey(i)) require.NoError(t, err) - require.Equal(t, ival(i), v) + if i < 5 { + require.Equal(t, ival(i*10), v) + } else { + require.Equal(t, ival(i), v) + } } view.Discard() // Load working version view = db.Reader() - for i := 100; i < 150; i++ { - v, err := view.Get(ikey(i)) - require.NoError(t, err) - require.Equal(t, ival(i), v) - } + val, err := view.Get(ikey(100)) + require.NoError(t, err) + require.Equal(t, ival(100), val) view.Discard() require.NoError(t, db.Close()) From f0edc67be5eb3c87653485060d79b2821da75a6a Mon Sep 17 00:00:00 2001 From: Roy Crihfield Date: Fri, 10 Sep 2021 20:23:21 +0800 Subject: [PATCH 8/8] Cleanup, suggestions from review --- db/README.md | 4 ++-- db/badgerdb/db.go | 54 +++++++++++++++++++++++++---------------------- 2 files changed, 31 insertions(+), 27 deletions(-) diff --git a/db/README.md b/db/README.md index d40862ef79b5..ab766bcbbc3c 100644 --- a/db/README.md +++ b/db/README.md @@ -38,9 +38,9 @@ This represents a self-contained and immutable view of a database's version hist The in-memory DB in the `db/memdb` package cannot be persisted to disk. It is implemented using the Google [btree](https://pkg.go.dev/github.com/google/btree) library. * This currently does not perform write conflict detection, so it only supports a single open write-transaction at a time. Multiple and concurrent read-transactions are supported. -### BadgerDB ### +### BadgerDB -A [BadgerDB](https://pkg.go.dev/github.com/dgraph-io/badger/v3)-based backend. Internally, this uses BadgerDB's "managed" mode for version management. +A [BadgerDB](https://pkg.go.dev/github.com/dgraph-io/badger/v3)-based backend. Internally, this uses BadgerDB's ["managed" mode](https://pkg.go.dev/github.com/dgraph-io/badger/v3#OpenManaged) for version management. Note that Badger only recognizes write conflicts for rows that are read _after_ a conflicting transaction was opened. In other words, the following will raise an error: ```go diff --git a/db/badgerdb/db.go b/db/badgerdb/db.go index 2a4cedc48378..413553000667 100644 --- a/db/badgerdb/db.go +++ b/db/badgerdb/db.go @@ -19,23 +19,24 @@ var ( versionsFilename string = "versions.csv" ) -var _ dbm.DBConnection = (*BadgerDB)(nil) -var _ dbm.DBReader = (*badgerTxn)(nil) -var _ dbm.DBWriter = (*badgerWriter)(nil) -var _ dbm.DBReadWriter = (*badgerWriter)(nil) +var ( + _ dbm.DBConnection = (*BadgerDB)(nil) + _ dbm.DBReader = (*badgerTxn)(nil) + _ dbm.DBWriter = (*badgerWriter)(nil) + _ dbm.DBReadWriter = (*badgerWriter)(nil) +) // BadgerDB is a connection to a BadgerDB key-value database. type BadgerDB struct { - db *badger.DB - vmgr *versionManager - mtx sync.RWMutex + db *badger.DB + vmgr *versionManager + mtx sync.RWMutex openWriters int32 } type badgerTxn struct { txn *badger.Txn - // vmgr *versionManager - db *BadgerDB + db *BadgerDB } type badgerWriter struct { @@ -55,15 +56,13 @@ type badgerIterator struct { // A badger Txn's commit TS must be strictly greater than a record's "last-read" // TS in order to detect conflicts, and a Txn must be read at a TS after last // commit to see current state. So we must use commit increments that are more -// granular than a version interval, mapping latter -> former. +// granular than our version interval, and map versions to the corresponding TS. type versionManager struct { *dbm.VersionManager - vmap versionTsMap + vmap map[uint64]uint64 lastTs uint64 } -type versionTsMap map[uint64]uint64 - // NewDB creates or loads a BadgerDB key-value database inside the given directory. // If dir does not exist, it will be created. func NewDB(dir string) (*BadgerDB, error) { @@ -73,7 +72,6 @@ func NewDB(dir string) (*BadgerDB, error) { return nil, err } opts := badger.DefaultOptions(dir) - // todo: NumVersionsToKeep opts.SyncWrites = false // note that we have Sync methods opts.Logger = nil // badger is too chatty by default return NewDBWithOptions(opts) @@ -110,24 +108,25 @@ func readVersionsFile(path string) (*versionManager, error) { return nil, err } var versions []uint64 - var ts uint64 - vmap := make(versionTsMap) + vmap := map[uint64]uint64{} for _, row := range rows { version, err := strconv.ParseUint(row[0], 10, 64) if err != nil { return nil, err } - ts, err = strconv.ParseUint(row[1], 10, 64) + ts, err := strconv.ParseUint(row[1], 10, 64) if err != nil { return nil, err } versions = append(versions, version) vmap[version] = ts } - if ts == 0 { - ts = 1 - } - return &versionManager{dbm.NewVersionManager(versions), vmap, ts}, nil + vmgr := dbm.NewVersionManager(versions) + return &versionManager{ + VersionManager: vmgr, + vmap: vmap, + lastTs: vmgr.Last(), + }, nil } // Write version metadata to CSV file @@ -377,19 +376,24 @@ func (i *badgerIterator) Value() []byte { func (vm *versionManager) versionTs(ver uint64) uint64 { return vm.vmap[ver] } + +// Atomically accesses the last commit timestamp used as a version marker. func (vm *versionManager) lastCommitTs() uint64 { return atomic.LoadUint64(&vm.lastTs) } func (vm *versionManager) Copy() *versionManager { + vmap := map[uint64]uint64{} + for ver, ts := range vm.vmap { + vmap[ver] = ts + } return &versionManager{ VersionManager: vm.VersionManager.Copy(), - vmap: vm.vmap, - lastTs: vm.lastTs, + vmap: vmap, + lastTs: vm.lastCommitTs(), } } // updateCommitTs atomically increments the lastTs if equal to readts. -// Returns the new value. func (vm *versionManager) updateCommitTs(readts uint64) { atomic.CompareAndSwapUint64(&vm.lastTs, readts, readts+1) } @@ -398,6 +402,6 @@ func (vm *versionManager) Save(target uint64) (uint64, error) { if err != nil { return 0, err } - vm.vmap[id] = atomic.LoadUint64(&vm.lastTs) + vm.vmap[id] = vm.lastTs // non-atomic, already guarded by the vmgr mutex return id, nil }