session: upgrade from old cluster infoschema v2 should not be used (#…

…56545) (#56738)

close #56544

br/pkg/restore/snap_client/systable_restore_test.go

@@ -116,5 +116,5 @@ func TestCheckSysTableCompatibility(t *testing.T) {
 //
 // The above variables are in the file br/pkg/restore/systable_restore.go
 func TestMonitorTheSystemTableIncremental(t *testing.T) {
-	require.Equal(t, int64(216), session.CurrentBootstrapVersion)
+	require.Equal(t, int64(217), session.CurrentBootstrapVersion)
 }

pkg/session/bootstrap.go

@@ -1182,11 +1182,15 @@ const (
 	// version 216
 	//   changes variable `tidb_scatter_region` value from ON to "table" and OFF to "".
 	version216 = 216
+
+	// version 217
+	// Keep tidb_schema_cache_size to 0 if this variable does not exist (upgrading from old version pre 8.1).
+	version217 = 217
 )
 
 // currentBootstrapVersion is defined as a variable, so we can modify its value for testing.
 // please make sure this is the largest version
-var currentBootstrapVersion int64 = version216
+var currentBootstrapVersion int64 = version217
 
 // DDL owner key's expired time is ManagerSessionTTL seconds, we should wait the time and give more time to have a chance to finish it.
 var internalSQLTimeout = owner.ManagerSessionTTL + 15
@@ -1358,6 +1362,7 @@ var (
 		upgradeToVer214,
 		upgradeToVer215,
 		upgradeToVer216,
+		upgradeToVer217,
 	}
 )
 
@@ -3267,6 +3272,15 @@ func upgradeToVer216(s sessiontypes.Session, ver int64) {
 	mustExecute(s, "UPDATE mysql.global_variables SET VARIABLE_VALUE='table' WHERE VARIABLE_NAME = 'tidb_scatter_region' AND VARIABLE_VALUE = 'ON'")
 }
 
+func upgradeToVer217(s sessiontypes.Session, ver int64) {
+	if ver >= version217 {
+		return
+	}
+	// If tidb_schema_cache_size does not exist, insert a record and set the value to 0
+	// Otherwise do nothing.
+	mustExecute(s, "INSERT IGNORE INTO mysql.global_variables VALUES ('tidb_schema_cache_size', 0)")
+}
+
 // initGlobalVariableIfNotExists initialize a global variable with specific val if it does not exist.
 func initGlobalVariableIfNotExists(s sessiontypes.Session, name string, val any) {
 	ctx := kv.WithInternalSourceType(context.Background(), kv.InternalTxnBootstrap)