sql: version-gate sql.txn.write_buffering_for_weak_isolation.enabled

Buffering writes in weak isolation levels such as read committed
requires lock loss detection to avoid intra-statement anomalies.

Lock loss detection is only available when all nodes are on 25.3 or
greater.

Epic: none
Release note: None

Author: stevendanna

pkg/ccl/logictestccl/testdata/logic_test/buffered_writes_lock_loss

@@ -1,4 +1,4 @@
-# LogicTest: !3node-tenant
+# LogicTest: !3node-tenant !local-mixed-25.2
 # cluster-opt: disable-mvcc-range-tombstones-for-point-deletes
 
 statement ok

pkg/ccl/logictestccl/tests/local-mixed-25.2/BUILD.bazel

@@ -9,7 +9,7 @@ go_test(
         "//pkg/ccl/logictestccl:testdata",  # keep
     ],
     exec_properties = {"test.Pool": "large"},
-    shard_count = 34,
+    shard_count = 33,
     tags = ["cpu:1"],
     deps = [
         "//pkg/base",

pkg/ccl/logictestccl/tests/local-mixed-25.2/generated_test.go

@@ -30,6 +30,7 @@ import (
 	"github.com/cockroachdb/cockroach/pkg/server/serverpb"
 	"github.com/cockroachdb/cockroach/pkg/server/telemetry"
 	"github.com/cockroachdb/cockroach/pkg/settings"
+	"github.com/cockroachdb/cockroach/pkg/settings/cluster"
 	"github.com/cockroachdb/cockroach/pkg/sql/appstatspb"
 	"github.com/cockroachdb/cockroach/pkg/sql/auditlogging"
 	"github.com/cockroachdb/cockroach/pkg/sql/catalog"
@@ -3543,9 +3544,7 @@ func (ex *connExecutor) setTransactionModes(
 		if err := ex.state.setIsolationLevel(level); err != nil {
 			return pgerror.WithCandidateCode(err, pgcode.ActiveSQLTransaction)
 		}
-		if (level != isolation.Serializable) && !allowBufferedWritesForWeakIsolation.Get(&ex.server.cfg.Settings.SV) {
-			// TODO(#143497): we currently only support buffered writes under
-			// serializable isolation.
+		if !ex.bufferedWritesIsAllowedForIsolationLevel(ctx, level) {
 			ex.state.mu.txn.SetBufferedWritesEnabled(false)
 		}
 	}
@@ -3731,6 +3730,28 @@ func (ex *connExecutor) bufferedWritesEnabled(ctx context.Context) bool {
 	return ex.sessionData().BufferedWritesEnabled && ex.server.cfg.Settings.Version.IsActive(ctx, clusterversion.V25_2)
 }
 
+func (ex *connExecutor) bufferedWritesIsAllowedForIsolationLevel(
+	ctx context.Context, isoLevel isolation.Level,
+) bool {
+	return bufferedWritesIsAllowedForIsolationLevel(ctx, ex.server.cfg.Settings, isoLevel)
+}
+
+func bufferedWritesIsAllowedForIsolationLevel(
+	ctx context.Context, st *cluster.Settings, isoLevel isolation.Level,
+) bool {
+	if isoLevel == isolation.Serializable {
+		return true
+	}
+
+	// We are at a weaker isolation level that requires lock loss detection which
+	// is only available on 25.3 or greater.
+	if !st.Version.IsActive(ctx, clusterversion.V25_3) {
+		return false
+	}
+
+	return allowBufferedWritesForWeakIsolation.Get(&st.SV)
+}
+
 // initEvalCtx initializes the fields of an extendedEvalContext that stay the
 // same across multiple statements. resetEvalCtx must also be called before each
 // statement, to reinitialize other fields.

pkg/sql/conn_executor.go

@@ -241,9 +241,7 @@ func (ts *txnState) resetForNewSQLTxn(
 			if err := ts.setIsolationLevelLocked(isoLevel); err != nil {
 				panic(err)
 			}
-			if isoLevel != isolation.Serializable && !allowBufferedWritesForWeakIsolation.Get(&tranCtx.settings.SV) {
-				// TODO(#143497): we currently only support buffered writes
-				// under serializable isolation.
+			if !bufferedWritesIsAllowedForIsolationLevel(connCtx, tranCtx.settings, isoLevel) {
 				bufferedWritesEnabled = false
 			}
 			if bufferedWritesEnabled {