MySQL: Use transaction_isolation instead of tx_isolation (#68575)

will use the correct system var name for transaction isolation

.github/CODEOWNERS

@@ -178,6 +178,7 @@
 /devenv/docker/blocks/influxdb1/ @grafana/observability-metrics
 /devenv/docker/blocks/jaeger/ @grafana/observability-traces-and-profiling
 /devenv/docker/blocks/maildev/ @grafana/alerting-squad-frontend
+/devenv/docker/blocks/mariadb/ @grafana/grafana-bi-squad
 /devenv/docker/blocks/memcached/ @grafana/backend-platform
 /devenv/docker/blocks/mssql/ @grafana/grafana-bi-squad
 /devenv/docker/blocks/mssql_arm64/ @grafana/grafana-bi-squad

devenv/docker/blocks/mariadb/docker-compose.yaml

@@ -0,0 +1,10 @@
+  mariadb:
+    image: mariadb:latest
+    restart: always
+    environment:
+      MARIADB_ROOT_PASSWORD: rootpass
+      MARIADB_DATABASE: grafana
+      MARIADB_USER: grafana
+      MARIADB_PASSWORD: password
+    ports:
+      - "3306:3306"

pkg/services/sqlstore/sqlstore.go

@@ -298,7 +298,7 @@ func (ss *SQLStore) buildConnectionString() (string, error) {
 
 		if isolation := ss.dbCfg.IsolationLevel; isolation != "" {
 			val := url.QueryEscape(fmt.Sprintf("'%s'", isolation))
-			cnnstr += fmt.Sprintf("&tx_isolation=%s", val)
+			cnnstr += fmt.Sprintf("&transaction_isolation=%s", val)
 		}
 
 		if ss.Cfg.IsFeatureToggleEnabled(featuremgmt.FlagMysqlAnsiQuotes) || ss.Cfg.IsFeatureToggleEnabled(featuremgmt.FlagNewDBLibrary) {
@@ -402,6 +402,14 @@ func (ss *SQLStore) initEngine(engine *xorm.Engine) error {
 		if err != nil {
 			return err
 		}
+		// Only for MySQL or MariaDB, verify we can connect with the current connection string's system var for transaction isolation.
+		// If not, create a new engine with a compatible connection string.
+		if ss.dbCfg.Type == migrator.MySQL {
+			engine, err = ss.ensureTransactionIsolationCompatibility(engine, connectionString)
+			if err != nil {
+				return err
+			}
+		}
 	}
 
 	engine.SetMaxOpenConns(ss.dbCfg.MaxOpenConn)
@@ -423,6 +431,32 @@ func (ss *SQLStore) initEngine(engine *xorm.Engine) error {
 	return nil
 }
 
+// The transaction_isolation system variable isn't compatible with MySQL < 5.7.20 or MariaDB. If we get an error saying this
+// system variable is unknown, then replace it with it's older version tx_isolation which is compatible with MySQL < 5.7.20 and MariaDB.
+func (ss *SQLStore) ensureTransactionIsolationCompatibility(engine *xorm.Engine, connectionString string) (*xorm.Engine, error) {
+	var result string
+	_, err := engine.SQL("SELECT 1").Get(&result)
+
+	var mysqlError *mysql.MySQLError
+	if errors.As(err, &mysqlError) {
+		// if there was an error due to transaction isolation
+		if strings.Contains(mysqlError.Message, "Unknown system variable 'transaction_isolation'") {
+			ss.log.Debug("transaction_isolation system var is unknown, overriding in connection string with tx_isolation instead")
+			// replace with compatible system var for transaction isolation
+			connectionString = strings.Replace(connectionString, "&transaction_isolation", "&tx_isolation", -1)
+			// recreate the xorm engine with new connection string that is compatible
+			engine, err = xorm.NewEngine(ss.dbCfg.Type, connectionString)
+			if err != nil {
+				return nil, err
+			}
+		}
+	} else if err != nil {
+		return nil, err
+	}
+
+	return engine, nil
+}
+
 // readConfig initializes the SQLStore from its configuration.
 func (ss *SQLStore) readConfig() error {
 	sec := ss.Cfg.Raw.Section("database")