Allow configuring the policy when prewrite encounters lock (#1501) (#1946)

ref pingcap/tidb#58675

Signed-off-by: ti-chi-bot <ti-community-prow-bot@tidb.io>
Signed-off-by: Chao Wang <cclcwangchao@hotmail.com>

Co-authored-by: ekexium <eke@fastmail.com>
Co-authored-by: Chao Wang <cclcwangchao@hotmail.com>

Author: 3 people

txnkv/transaction/prewrite.go

@@ -478,6 +478,7 @@ func (action actionPrewrite) handleSingleBatch(
 					zap.Uint64("session", c.sessionID),
 					zap.Uint64("txnID", c.startTS),
 					zap.Stringer("lock", lock),
+					zap.Stringer("policy", c.txn.prewriteEncounterLockPolicy),
 				)
 				logged[lock.TxnID] = struct{}{}
 			}
@@ -486,7 +487,8 @@ func (action actionPrewrite) handleSingleBatch(
 			// Pessimistic transactions don't need such an optimization. If this key needs a pessimistic lock,
 			// TiKV will return a PessimisticLockNotFound error directly if it encounters a different lock. Otherwise,
 			// TiKV returns lock.TTL = 0, and we still need to resolve the lock.
-			if lock.TxnID > c.startTS && !c.isPessimistic {
+			if (lock.TxnID > c.startTS && !c.isPessimistic) ||
+				c.txn.prewriteEncounterLockPolicy == NoResolvePolicy {
 				return tikverr.NewErrWriteConflictWithArgs(
 					c.startTS,
 					lock.TxnID,

txnkv/transaction/txn.go

@@ -118,6 +118,28 @@ type TxnOptions struct {
 	PipelinedMemDB bool
 }
 
+// PrewriteEncounterLockPolicy specifies the policy when prewrite encounters locks.
+type PrewriteEncounterLockPolicy int
+
+const (
+	// TryResolvePolicy is the default one: try to resolve those locks with smaller startTS.
+	TryResolvePolicy PrewriteEncounterLockPolicy = iota
+	// NoResolvePolicy means do not resolve, but return write conflict errors directly.
+	// This can be used to let the upper layer choose to retry in pessimistic mode.
+	NoResolvePolicy
+)
+
+func (p PrewriteEncounterLockPolicy) String() string {
+	switch p {
+	case TryResolvePolicy:
+		return "TryResolvePolicy"
+	case NoResolvePolicy:
+		return "NoResolvePolicy"
+	default:
+		return "Unknown"
+	}
+}
+
 // KVTxn contains methods to interact with a TiKV transaction.
 type KVTxn struct {
 	snapshot  *txnsnapshot.KVSnapshot
@@ -187,6 +209,8 @@ type KVTxn struct {
 		firstAttemptTS uint64
 		backoffCnt     int
 	}
+
+	prewriteEncounterLockPolicy PrewriteEncounterLockPolicy
 }
 
 // NewTiKVTxn creates a new KVTxn.
@@ -513,6 +537,11 @@ func (txn *KVTxn) SetAssertionLevel(assertionLevel kvrpcpb.AssertionLevel) {
 	txn.assertionLevel = assertionLevel
 }
 
+// SetPrewriteEncounterLockPolicy specifies the behavior when prewrite encounters locks.
+func (txn *KVTxn) SetPrewriteEncounterLockPolicy(policy PrewriteEncounterLockPolicy) {
+	txn.prewriteEncounterLockPolicy = policy
+}
+
 // IsPessimistic returns true if it is pessimistic.
 func (txn *KVTxn) IsPessimistic() bool {
 	return txn.isPessimistic