sql: don't consider repeatable read to snapshot an upgrade

One isolation level is not stronger than the other. We consider
them aliases of each other.

Epic: None
Release note: None

pkg/sql/conn_executor.go

@@ -3529,9 +3529,7 @@ var allowReadCommittedIsolation = settings.RegisterBoolSetting(
 	settings.WithPublic,
 )
 
-// TODO(nvanbenschoten): rename this variable and update uses of it to favor
-// "repeatable read" over "snapshot".
-var allowSnapshotIsolation = settings.RegisterBoolSetting(
+var allowRepeatableReadIsolation = settings.RegisterBoolSetting(
 	settings.ApplicationLevel,
 	"sql.txn.snapshot_isolation.enabled",
 	"set to true to allow transactions to use the REPEATABLE READ isolation "+
@@ -3589,20 +3587,17 @@ func (ex *connExecutor) txnIsolationLevelToKV(
 				upgradedDueToLicense = true
 			}
 		}
-	case tree.RepeatableReadIsolation:
-		// REPEATABLE READ is mapped to SNAPSHOT.
-		upgraded = true
-		fallthrough
-	case tree.SnapshotIsolation:
-		// SNAPSHOT is only allowed if the cluster setting is enabled and the
-		// cluster has a license. Otherwise it is mapped to SERIALIZABLE.
-		allowSnapshot := allowSnapshotIsolation.Get(&ex.server.cfg.Settings.SV)
-		if allowSnapshot && hasLicense {
+	case tree.RepeatableReadIsolation, tree.SnapshotIsolation:
+		// REPEATABLE READ and SNAPSHOT are considered aliases. The isolation levels
+		// are only allowed if the cluster setting is enabled and the cluster has a
+		// license. Otherwise, they are mapped to SERIALIZABLE.
+		allowRepeatableRead := allowRepeatableReadIsolation.Get(&ex.server.cfg.Settings.SV)
+		if allowRepeatableRead && hasLicense {
 			ret = isolation.Snapshot
 		} else {
 			upgraded = true
 			ret = isolation.Serializable
-			if allowSnapshot && !hasLicense {
+			if allowRepeatableRead && !hasLicense {
 				upgradedDueToLicense = true
 			}
 		}

pkg/sql/set_session_characteristics.go

@@ -28,7 +28,7 @@ func (p *planner) SetSessionCharacteristics(
 	upgradedLevel := false
 	upgradedDueToLicense := false
 	allowReadCommitted := allowReadCommittedIsolation.Get(&p.execCfg.Settings.SV)
-	allowSnapshot := allowSnapshotIsolation.Get(&p.execCfg.Settings.SV)
+	allowRepeatableRead := allowRepeatableReadIsolation.Get(&p.execCfg.Settings.SV)
 	hasLicense := base.CCLDistributionAndEnterpriseEnabled(p.ExecCfg().Settings)
 	if err := p.sessionDataMutatorIterator.applyOnEachMutatorError(func(m sessionDataMutator) error {
 		// Note: We also support SET DEFAULT_TRANSACTION_ISOLATION TO ' .... '.
@@ -49,16 +49,13 @@ func (p *planner) SetSessionCharacteristics(
 				}
 			}
 			m.SetDefaultTransactionIsolationLevel(level)
-		case tree.RepeatableReadIsolation:
-			upgradedLevel = true
-			fallthrough
-		case tree.SnapshotIsolation:
+		case tree.RepeatableReadIsolation, tree.SnapshotIsolation:
 			level := tree.SerializableIsolation
-			if allowSnapshot && hasLicense {
+			if allowRepeatableRead && hasLicense {
 				level = tree.SnapshotIsolation
 			} else {
 				upgradedLevel = true
-				if allowSnapshot && !hasLicense {
+				if allowRepeatableRead && !hasLicense {
 					upgradedDueToLicense = true
 				}
 			}

pkg/sql/testdata/telemetry/isolation_level

@@ -112,7 +112,6 @@ feature-usage
 SET default_transaction_isolation = 'repeatable read'
 ----
 sql.txn.isolation.executed_at.read_committed
-sql.txn.isolation.upgraded_from.repeatable_read
 
 feature-usage
 SET default_transaction_isolation = 'snapshot'
@@ -134,7 +133,6 @@ feature-usage
 SET SESSION CHARACTERISTICS AS TRANSACTION ISOLATION LEVEL REPEATABLE READ
 ----
 sql.txn.isolation.executed_at.read_committed
-sql.txn.isolation.upgraded_from.repeatable_read
 
 feature-usage
 SET SESSION CHARACTERISTICS AS TRANSACTION ISOLATION LEVEL SNAPSHOT
@@ -156,7 +154,6 @@ feature-usage
 BEGIN TRANSACTION ISOLATION LEVEL REPEATABLE READ; COMMIT
 ----
 sql.txn.isolation.executed_at.snapshot
-sql.txn.isolation.upgraded_from.repeatable_read
 
 feature-usage
 BEGIN TRANSACTION ISOLATION LEVEL SNAPSHOT; COMMIT
@@ -180,7 +177,6 @@ feature-usage
 BEGIN; SET TRANSACTION ISOLATION LEVEL REPEATABLE READ; COMMIT
 ----
 sql.txn.isolation.executed_at.snapshot
-sql.txn.isolation.upgraded_from.repeatable_read
 
 feature-usage
 BEGIN; SET TRANSACTION ISOLATION LEVEL SNAPSHOT; COMMIT

pkg/sql/testdata/telemetry_logging/logging/stmts_per_txn_limit

@@ -228,4 +228,3 @@ BEGIN; SELECT 1; SELECT 2; SELECT 3; SELECT 4; COMMIT;
 	"TransactionFingerprintID": "2831371359051261045",
 	"User": "root"
 }
-

pkg/sql/vars.go

@@ -418,10 +418,10 @@ var varGen = map[string]sessionVar{
 	`default_transaction_isolation`: {
 		Set: func(ctx context.Context, m sessionDataMutator, s string) error {
 			allowReadCommitted := allowReadCommittedIsolation.Get(&m.settings.SV)
-			allowSnapshot := allowSnapshotIsolation.Get(&m.settings.SV)
+			allowRepeatableRead := allowRepeatableReadIsolation.Get(&m.settings.SV)
 			hasLicense := base.CCLDistributionAndEnterpriseEnabled(m.settings)
 			var allowedValues = []string{"serializable"}
-			if allowSnapshot {
+			if allowRepeatableRead {
 				// TODO(nvanbenschoten): switch to "repeatable read".
 				allowedValues = append(allowedValues, "snapshot")
 			}
@@ -449,16 +449,13 @@ var varGen = map[string]sessionVar{
 						upgradedDueToLicense = true
 					}
 				}
-			case tree.RepeatableReadIsolation:
-				upgraded = true
-				fallthrough
-			case tree.SnapshotIsolation:
+			case tree.RepeatableReadIsolation, tree.SnapshotIsolation:
 				level = tree.SerializableIsolation
-				if allowSnapshot && hasLicense {
+				if allowRepeatableRead && hasLicense {
 					level = tree.SnapshotIsolation
 				} else {
 					upgraded = true
-					if allowSnapshot && !hasLicense {
+					if allowRepeatableRead && !hasLicense {
 						upgradedDueToLicense = true
 					}
 				}
@@ -1615,7 +1612,7 @@ var varGen = map[string]sessionVar{
 			level, ok := tree.IsolationLevelMap[strings.ToLower(s)]
 			if !ok {
 				var allowedValues = []string{"serializable"}
-				if allowSnapshotIsolation.Get(&evalCtx.ExecCfg.Settings.SV) {
+				if allowRepeatableReadIsolation.Get(&evalCtx.ExecCfg.Settings.SV) {
 					// TODO(nvanbenschoten): switch to "repeatable read".
 					allowedValues = append(allowedValues, "snapshot")
 				}