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mvcc: fully concurrent read

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This commit is contained in:
Jingyi Hu 2019-03-06 17:43:48 -08:00
parent 88922b0d08
commit a73fb85c0c
8 changed files with 231 additions and 47 deletions
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46
integration/metrics_test.go
View File

@ -16,6 +16,7 @@ package integration
import (
"context"
"fmt"
"net/http"
"strconv"
"testing"
@ -103,22 +104,39 @@ func testMetricDbSizeDefrag(t *testing.T, name string) {
t.Fatal(kerr)
}
// Put to move PendingPages to FreePages
if _, err = kvc.Put(context.TODO(), putreq); err != nil {
t.Fatal(err)
}
time.Sleep(500 * time.Millisecond)
validateAfterCompactionInUse := func() error {
// Put to move PendingPages to FreePages
if _, err = kvc.Put(context.TODO(), putreq); err != nil {
t.Fatal(err)
}
time.Sleep(500 * time.Millisecond)
afterCompactionInUse, err := clus.Members[0].Metric("etcd_mvcc_db_total_size_in_use_in_bytes")
if err != nil {
t.Fatal(err)
afterCompactionInUse, err := clus.Members[0].Metric("etcd_mvcc_db_total_size_in_use_in_bytes")
if err != nil {
t.Fatal(err)
}
aciu, err := strconv.Atoi(afterCompactionInUse)
if err != nil {
t.Fatal(err)
}
if biu <= aciu {
return fmt.Errorf("expected less than %d, got %d after compaction", biu, aciu)
}
return nil
}
aciu, err := strconv.Atoi(afterCompactionInUse)
if err != nil {
t.Fatal(err)
}
if biu <= aciu {
t.Fatalf("expected less than %d, got %d after compaction", biu, aciu)
// backend rollbacks read transaction asynchronously (PR #10523),
// which causes the result to be flaky. Retry 3 times.
maxRetry, retry := 3, 0
for {
err := validateAfterCompactionInUse()
if err == nil {
break
}
retry++
if retry >= maxRetry {
t.Fatalf(err.Error())
}
}
// defrag should give freed space back to fs

20
mvcc/backend/backend.go
View File

@ -51,6 +51,8 @@ var (
type Backend interface {
ReadTx() ReadTx
BatchTx() BatchTx
// ConcurrentReadTx returns a non-blocking read transaction.
ConcurrentReadTx() ReadTx
Snapshot() Snapshot
Hash(ignores map[IgnoreKey]struct{}) (uint32, error)
@ -166,6 +168,7 @@ func newBackend(bcfg BackendConfig) *backend {
txBuffer: txBuffer{make(map[string]*bucketBuffer)},
},
buckets: make(map[string]*bolt.Bucket),
txWg: new(sync.WaitGroup),
},
stopc: make(chan struct{}),
@ -187,6 +190,23 @@ func (b *backend) BatchTx() BatchTx {
func (b *backend) ReadTx() ReadTx { return b.readTx }
// ConcurrentReadTx creates and returns a new ReadTx, which:
// A) creates and keeps a copy of backend.readTx.txReadBuffer,
// B) references the boltdb read Tx (and its bucket cache) of current batch interval.
func (b *backend) ConcurrentReadTx() ReadTx {
b.readTx.RLock()
defer b.readTx.RUnlock()
// prevent boltdb read Tx from been rolled back until store read Tx is done.
b.readTx.txWg.Add(1)
return &concurrentReadTx{
buf: b.readTx.buf.unsafeCopy(),
tx: b.readTx.tx,
txMu: &b.readTx.txMu,
buckets: b.readTx.buckets,
txWg: b.readTx.txWg,
}
}
// ForceCommit forces the current batching tx to commit.
func (b *backend) ForceCommit() {
b.batchTx.Commit()

2
mvcc/backend/backend_test.go
View File

@ -300,6 +300,8 @@ func TestBackendWritebackForEach(t *testing.T) {
}
}
// TODO: add a unit test for concurrentReadTx
func cleanup(b Backend, path string) {
b.Close()
os.Remove(path)

21
mvcc/backend/batch_tx.go
View File

@ -306,13 +306,9 @@ func (t *batchTxBuffered) commit(stop bool) {
func (t *batchTxBuffered) unsafeCommit(stop bool) {
if t.backend.readTx.tx != nil {
if err := t.backend.readTx.tx.Rollback(); err != nil {
if t.backend.lg != nil {
t.backend.lg.Fatal("failed to rollback tx", zap.Error(err))
} else {
plog.Fatalf("cannot rollback tx (%s)", err)
}
}
// wait all store read transactions using the current boltdb tx to finish,
// then close the boltdb tx
go waitAndRollback(t.backend.readTx.tx, t.backend.readTx.txWg, t.backend.lg)
t.backend.readTx.reset()
}
@ -323,6 +319,17 @@ func (t *batchTxBuffered) unsafeCommit(stop bool) {
}
}
func waitAndRollback(tx *bolt.Tx, wg *sync.WaitGroup, lg *zap.Logger) {
wg.Wait()
if err := tx.Rollback(); err != nil {
if lg != nil {
lg.Fatal("failed to rollback tx", zap.Error(err))
} else {
plog.Fatalf("cannot rollback tx (%s)", err)
}
}
}
func (t *batchTxBuffered) UnsafePut(bucketName []byte, key []byte, value []byte) {
t.batchTx.UnsafePut(bucketName, key, value)
t.buf.put(bucketName, key, value)

102
mvcc/backend/read_tx.go
View File

@ -42,10 +42,13 @@ type readTx struct {
mu sync.RWMutex
buf txReadBuffer
// txmu protects accesses to buckets and tx on Range requests.
txmu sync.RWMutex
// TODO: group and encapsulate {txMu, tx, buckets, txWg}, as they share the same lifecycle.
// txMu protects accesses to buckets and tx on Range requests.
txMu sync.RWMutex
tx *bolt.Tx
buckets map[string]*bolt.Bucket
// txWg protects tx from being rolled back at the end of a batch interval until all reads using this tx are done.
txWg *sync.WaitGroup
}
func (rt *readTx) Lock() { rt.mu.Lock() }
@ -71,23 +74,23 @@ func (rt *readTx) UnsafeRange(bucketName, key, endKey []byte, limit int64) ([][]
// find/cache bucket
bn := string(bucketName)
rt.txmu.RLock()
rt.txMu.RLock()
bucket, ok := rt.buckets[bn]
rt.txmu.RUnlock()
rt.txMu.RUnlock()
if !ok {
rt.txmu.Lock()
rt.txMu.Lock()
bucket = rt.tx.Bucket(bucketName)
rt.buckets[bn] = bucket
rt.txmu.Unlock()
rt.txMu.Unlock()
}
// ignore missing bucket since may have been created in this batch
if bucket == nil {
return keys, vals
}
rt.txmu.Lock()
rt.txMu.Lock()
c := bucket.Cursor()
rt.txmu.Unlock()
rt.txMu.Unlock()
k2, v2 := unsafeRange(c, key, endKey, limit-int64(len(keys)))
return append(k2, keys...), append(v2, vals...)
@ -108,9 +111,9 @@ func (rt *readTx) UnsafeForEach(bucketName []byte, visitor func(k, v []byte) err
if err := rt.buf.ForEach(bucketName, getDups); err != nil {
return err
}
rt.txmu.Lock()
rt.txMu.Lock()
err := unsafeForEach(rt.tx, bucketName, visitNoDup)
rt.txmu.Unlock()
rt.txMu.Unlock()
if err != nil {
return err
}
@ -121,4 +124,83 @@ func (rt *readTx) reset() {
rt.buf.reset()
rt.buckets = make(map[string]*bolt.Bucket)
rt.tx = nil
rt.txWg = new(sync.WaitGroup)
}
// TODO: create a base type for readTx and concurrentReadTx to avoid duplicated function implementation?
type concurrentReadTx struct {
buf txReadBuffer
txMu *sync.RWMutex
tx *bolt.Tx
buckets map[string]*bolt.Bucket // note: A map value is a pointer
txWg *sync.WaitGroup
}
func (rt *concurrentReadTx) Lock() {}
func (rt *concurrentReadTx) Unlock() {}
func (rt *concurrentReadTx) RLock() {}
func (rt *concurrentReadTx) RUnlock() { rt.txWg.Done() }
func (rt *concurrentReadTx) UnsafeForEach(bucketName []byte, visitor func(k, v []byte) error) error {
dups := make(map[string]struct{})
getDups := func(k, v []byte) error {
dups[string(k)] = struct{}{}
return nil
}
visitNoDup := func(k, v []byte) error {
if _, ok := dups[string(k)]; ok {
return nil
}
return visitor(k, v)
}
if err := rt.buf.ForEach(bucketName, getDups); err != nil {
return err
}
rt.txMu.Lock()
err := unsafeForEach(rt.tx, bucketName, visitNoDup)
rt.txMu.Unlock()
if err != nil {
return err
}
return rt.buf.ForEach(bucketName, visitor)
}
func (rt *concurrentReadTx) UnsafeRange(bucketName, key, endKey []byte, limit int64) ([][]byte, [][]byte) {
if endKey == nil {
// forbid duplicates for single keys
limit = 1
}
if limit <= 0 {
limit = math.MaxInt64
}
if limit > 1 && !bytes.Equal(bucketName, safeRangeBucket) {
panic("do not use unsafeRange on non-keys bucket")
}
keys, vals := rt.buf.Range(bucketName, key, endKey, limit)
if int64(len(keys)) == limit {
return keys, vals
}
// find/cache bucket
bn := string(bucketName)
rt.txMu.RLock()
bucket, ok := rt.buckets[bn]
rt.txMu.RUnlock()
if !ok {
rt.txMu.Lock()
bucket = rt.tx.Bucket(bucketName)
rt.buckets[bn] = bucket
rt.txMu.Unlock()
}
// ignore missing bucket since may have been created in this batch
if bucket == nil {
return keys, vals
}
rt.txMu.Lock()
c := bucket.Cursor()
rt.txMu.Unlock()
k2, v2 := unsafeRange(c, key, endKey, limit-int64(len(keys)))
return append(k2, keys...), append(v2, vals...)
}

22
mvcc/backend/tx_buffer.go
View File

@ -88,6 +88,19 @@ func (txr *txReadBuffer) ForEach(bucketName []byte, visitor func(k, v []byte) er
return nil
}
// unsafeCopy returns a copy of txReadBuffer, caller should acquire backend.readTx.RLock()
func (txr *txReadBuffer) unsafeCopy() txReadBuffer {
txrCopy := txReadBuffer{
txBuffer: txBuffer{
buckets: make(map[string]*bucketBuffer, len(txr.txBuffer.buckets)),
},
}
for bucketName, bucket := range txr.txBuffer.buckets {
txrCopy.txBuffer.buckets[bucketName] = bucket.Copy()
}
return txrCopy
}
type kv struct {
key []byte
val []byte
@ -179,3 +192,12 @@ func (bb *bucketBuffer) Less(i, j int) bool {
return bytes.Compare(bb.buf[i].key, bb.buf[j].key) < 0
}
func (bb *bucketBuffer) Swap(i, j int) { bb.buf[i], bb.buf[j] = bb.buf[j], bb.buf[i] }
func (bb *bucketBuffer) Copy() *bucketBuffer {
bbCopy := bucketBuffer{
buf: make([]kv, len(bb.buf)),
used: bb.used,
}
copy(bbCopy.buf, bb.buf)
return &bbCopy
}

56
mvcc/kvstore_test.go
View File

@ -645,30 +645,65 @@ func TestTxnPut(t *testing.T) {
}
}
func TestTxnBlockBackendForceCommit(t *testing.T) {
func TestConcurrentReadAndWrite(t *testing.T) {
b, tmpPath := backend.NewDefaultTmpBackend()
s := NewStore(zap.NewExample(), b, &lease.FakeLessor{}, nil)
defer os.Remove(tmpPath)
txn := s.Read()
// write something to read later
s.Put([]byte("foo"), []byte("bar"), lease.NoLease)
// readTx simulates a long read request
readTx1 := s.Read()
// write should not be blocked by reads
done := make(chan struct{})
go func() {
s.b.ForceCommit()
s.Put([]byte("foo"), []byte("newBar"), lease.NoLease) // this is a write Txn
done <- struct{}{}
}()
select {
case <-done:
t.Fatalf("failed to block ForceCommit")
case <-time.After(100 * time.Millisecond):
case <-time.After(1 * time.Second):
t.Fatalf("write should not be blocked by read")
}
txn.End()
select {
case <-done:
case <-time.After(5 * time.Second): // wait 5 seconds for CI with slow IO
testutil.FatalStack(t, "failed to execute ForceCommit")
// readTx2 simulates a short read request
readTx2 := s.Read()
ro := RangeOptions{Limit: 1, Rev: 0, Count: false}
ret, err := readTx2.Range([]byte("foo"), nil, ro)
if err != nil {
t.Fatalf("failed to range: %v", err)
}
// readTx2 should see the result of new write
w := mvccpb.KeyValue{
Key: []byte("foo"),
Value: []byte("newBar"),
CreateRevision: 2,
ModRevision: 3,
Version: 2,
}
if !reflect.DeepEqual(ret.KVs[0], w) {
t.Fatalf("range result = %+v, want = %+v", ret.KVs[0], w)
}
readTx2.End()
ret, err = readTx1.Range([]byte("foo"), nil, ro)
if err != nil {
t.Fatalf("failed to range: %v", err)
}
// readTx1 should not see the result of new write
w = mvccpb.KeyValue{
Key: []byte("foo"),
Value: []byte("bar"),
CreateRevision: 2,
ModRevision: 2,
Version: 1,
}
if !reflect.DeepEqual(ret.KVs[0], w) {
t.Fatalf("range result = %+v, want = %+v", ret.KVs[0], w)
}
readTx1.End()
}
// TODO: test attach key to lessor
@ -754,6 +789,7 @@ type fakeBackend struct {
func (b *fakeBackend) BatchTx() backend.BatchTx { return b.tx }
func (b *fakeBackend) ReadTx() backend.ReadTx { return b.tx }
func (b *fakeBackend) ConcurrentReadTx() backend.ReadTx { return b.tx }
func (b *fakeBackend) Hash(ignores map[backend.IgnoreKey]struct{}) (uint32, error) { return 0, nil }
func (b *fakeBackend) Size() int64 { return 0 }
func (b *fakeBackend) SizeInUse() int64 { return 0 }

9
mvcc/kvstore_txn.go
View File

@ -31,13 +31,10 @@ type storeTxnRead struct {
func (s *store) Read() TxnRead {
s.mu.RLock()
tx := s.b.ReadTx()
s.revMu.RLock()
// tx.RLock() blocks txReadBuffer for reading, which could potentially block the following two operations:
// A) writeback from txWriteBuffer to txReadBuffer at the end of a write transaction (TxnWrite).
// B) starting of a new backend batch transaction, where the pending changes need to be committed to boltdb
// and txReadBuffer needs to be reset.
tx.RLock()
// backend holds b.readTx.RLock() only when creating the concurrentReadTx. After
// ConcurrentReadTx is created, it will not block write transaction.
tx := s.b.ConcurrentReadTx()
firstRev, rev := s.compactMainRev, s.currentRev
s.revMu.RUnlock()
return newMetricsTxnRead(&storeTxnRead{s, tx, firstRev, rev})