kv: clarify return value on EndTxnResponse

Addresses a TODO from the last commit.

Epic: none

Release note: None

Author: arulajmani

pkg/kv/kvpb/api.proto

@@ -1027,18 +1027,24 @@ message EndTxnResponse {
   // The commit timestamp of the STAGING transaction record written
   // by the request. Only set if the transaction record was staged.
   util.hlc.Timestamp staging_timestamp = 5 [(gogoproto.nullable) = false];
-  // ReplicatedLocksReleasedOnCommit, if non-empty, indicate that replicated
-  // locks with strength Shared or Exclusive were released in the referenced key
-  // spans when committing this transaction. Notably, this field is left unset
-  // if only write intents were resolved. The field is also left unset for
-  // transactions that aborted.
+  // ReplicatedLocalLocksReleasedOnCommit, if non-empty, indicate that
+  // replicated locks with strength Shared or Exclusive were released in the
+  // referenced key spans when committing this transaction. These locks are
+  // local to the range on which the EndTxn request evaluated. Notably, this
+  // field is left unset if only write intents were resolved. The field is only
+  // set when transactions are explicitly marked as committed.
   //
   // The caller must bump the timestamp cache across these spans to the
-  // transaction's commit timestamp. Doing so ensures that the released locks
-  // (acquired by the now committed transaction) continue to provide protection
-  // against other writers up to the commit timestamp, even after the locks have
-  // been released.
-  repeated Span replicated_locks_released_on_commit = 6 [(gogoproto.nullable) = false];
+  // transaction's commit timestamp. Doing so ensures that the released local[1]
+  // locks (acquired by the now committed transaction) continue to provide
+  // protection against other writers up to the commit timestamp, even after the
+  // locks have been released.
+  //
+  // [1] Non-local replicated locks provide the same protection, however, the
+  // mechanism of bumping the timestamp cache is different there. See the
+  // ReplicatedLocksReleasedCommitTimestamp field on
+  // ResolveIntent{,Range}Response.
+  repeated Span replicated_local_locks_released_on_commit = 6 [(gogoproto.nullable) = false];
 }
 
 // An AdminSplitRequest is the argument to the AdminSplit() method. The

pkg/kv/kvserver/batcheval/cmd_end_transaction.go

@@ -560,9 +560,7 @@ func EndTxn(
 			// transaction's commit timestamp to the key spans previously protected by
 			// the locks. We return the spans on the response and update the timestamp
 			// cache a few layers above to ensure this.
-			//
-			// TODO(arul): rename this to include the word local in it.
-			reply.ReplicatedLocksReleasedOnCommit = releasedReplLocks
+			reply.ReplicatedLocalLocksReleasedOnCommit = releasedReplLocks
 			log.VEventf(
 				ctx, 2, "committed transaction released local replicated shared/exclusive locks",
 			)

pkg/kv/kvserver/replica_tscache.go

@@ -170,12 +170,12 @@ func (r *Replica) updateTimestampCache(
 			// transaction's MinTimestamp, which is consulted in CanCreateTxnRecord.
 			key := transactionTombstoneMarker(start, txnID)
 			addToTSCache(key, nil, ts, txnID)
-			// Additionally, EndTxn requests that release replicated locks for
-			// committed transactions bump the timestamp cache over those lock
-			// spans to the commit timestamp of the transaction to ensure that
-			// the released locks continue to provide protection against writes
-			// underneath the transaction's commit timestamp.
-			for _, sp := range resp.(*kvpb.EndTxnResponse).ReplicatedLocksReleasedOnCommit {
+			// Additionally, EndTxn requests that release local replicated locks for
+			// committed transactions bump the timestamp cache over those lock spans
+			// to the commit timestamp of the transaction to ensure that the released
+			// locks continue to provide protection against writes underneath the
+			// transaction's commit timestamp.
+			for _, sp := range resp.(*kvpb.EndTxnResponse).ReplicatedLocalLocksReleasedOnCommit {
 				addToTSCache(sp.Key, sp.EndKey, br.Txn.WriteTimestamp, txnID)
 			}
 		case *kvpb.HeartbeatTxnRequest: