store/tikv: define KVFilter for customized mutation initialization

store/driver/txn/txn_driver.go

@@ -32,6 +32,7 @@ type tikvTxn struct {
 
 // NewTiKVTxn returns a new Transaction.
 func NewTiKVTxn(txn *tikv.KVTxn) kv.Transaction {
+ txn.SetOption(tikvstore.KVFilter, TiDBKVFilter{})
  return &tikvTxn{txn, make(map[int64]*model.TableInfo)}
 }
 
@@ -141,3 +142,11 @@ func (txn *tikvTxn) extractKeyExistsErr(key kv.Key) error {
  }
  return extractKeyExistsErrFromIndex(key, value, tblInfo, indexID)
 }
+
+// TiDBKVFilter is the filter specific to TiDB to filter out KV pairs that needn't be committed.
+type TiDBKVFilter struct{}
+
+// IsUnnecessaryKeyValue defines which kinds of KV pairs from TiDB needn't be committed.
+func (f TiDBKVFilter) IsUnnecessaryKeyValue(key, value []byte, flags tikvstore.KeyFlags) bool {
+ return tablecodec.IsUntouchedIndexKValue(key, value)
+}

store/tikv/2pc.go

@@ -314,6 +314,12 @@ func (c *twoPhaseCommitter) extractKeyExistsErr(err *kv.ErrKeyExist) error {
  return errors.Trace(err)
 }
 
+// KVFilter is a filter that filters out unnecessary KV pairs.
+type KVFilter interface {
+ // IsUnnecessaryKeyValue returns whether this KV pair should be committed.
+ IsUnnecessaryKeyValue(key, value []byte, flags kv.KeyFlags) bool
+}
+
 func (c *twoPhaseCommitter) initKeysAndMutations() error {
  var size, putCnt, delCnt, lockCnt, checkCnt int
 
@@ -322,6 +328,7 @@ func (c *twoPhaseCommitter) initKeysAndMutations() error {
  sizeHint := txn.us.GetMemBuffer().Len()
  c.mutations = newMemBufferMutations(sizeHint, memBuf)
  c.isPessimistic = txn.IsPessimistic()
+ filter := txn.getKVFilter()
 
  var err error
  for it := memBuf.IterWithFlags(nil, nil); it.Valid(); err = it.Next() {
@@ -340,10 +347,14 @@ func (c *twoPhaseCommitter) initKeysAndMutations() error {
  } else {
  value = it.Value()
  if len(value) > 0 {
- if tablecodec.IsUntouchedIndexKValue(key, value) {
+ isUnnecessaryKV := filter != nil && filter.IsUnnecessaryKeyValue(key, value, flags)
+ if isUnnecessaryKV {
  if !flags.HasLocked() {
  continue
  }
+ // If the key was locked before, we should prewrite the lock even if
+ // the KV needn't be committed according to the filter. Otherwise, we
+ // were forgetting removing pessimistic locks added before.
  op = pb.Op_Lock
  lockCnt++
  } else {

store/tikv/kv/option.go

@@ -59,6 +59,8 @@ const (
  IsStalenessReadOnly
  // MatchStoreLabels indicates the labels the store should be matched
  MatchStoreLabels
+ // KVFilter filters out the key-value pairs in the memBuf that is unnecessary to be committed
+ KVFilter
 )
 
 // Priority value for transaction priority.

store/tikv/tests/2pc_test.go

@@ -30,6 +30,7 @@ import (
  "github.com/pingcap/kvproto/pkg/kvrpcpb"
  pb "github.com/pingcap/kvproto/pkg/kvrpcpb"
  tidbkv "github.com/pingcap/tidb/kv"
+ drivertxn "github.com/pingcap/tidb/store/driver/txn"
  "github.com/pingcap/tidb/store/mockstore/mocktikv"
  "github.com/pingcap/tidb/store/tikv"
  "github.com/pingcap/tidb/store/tikv/config"
@@ -1032,6 +1033,7 @@ func (s *testCommitterSuite) TestResolvePessimisticLock(c *C) {
  noValueIndexKey := []byte("t00000001_i000000002")
  c.Assert(tablecodec.IsUntouchedIndexKValue(untouchedIndexKey, untouchedIndexValue), IsTrue)
  txn := s.begin(c)
+ txn.SetOption(kv.KVFilter, drivertxn.TiDBKVFilter{})
  err := txn.Set(untouchedIndexKey, untouchedIndexValue)
  c.Assert(err, IsNil)
  lockCtx := &kv.LockCtx{ForUpdateTS: txn.StartTS(), WaitStartTime: time.Now(), LockWaitTime: tidbkv.LockNoWait}

store/tikv/txn.go

@@ -214,6 +214,13 @@ func (txn *KVTxn) IsPessimistic() bool {
  return txn.us.GetOption(kv.Pessimistic) != nil
 }
 
+func (txn *KVTxn) getKVFilter() KVFilter {
+ if filter := txn.us.GetOption(kv.KVFilter); filter != nil {
+ return filter.(KVFilter)
+ }
+ return nil
+}
+
 // Commit commits the transaction operations to KV store.
 func (txn *KVTxn) Commit(ctx context.Context) error {
  if span := opentracing.SpanFromContext(ctx); span != nil && span.Tracer() != nil {