SQL Engine: Revert session changes (#64594)

Revert session changes

pkg/tsdb/sqleng/sql_engine.go

@@ -101,7 +101,6 @@ type DataSourceHandler struct {
 	log                    log.Logger
 	dsInfo                 DataSourceInfo
 	rowLimit               int64
-	session                *xorm.Session
 }
 
 type QueryJson struct {
@@ -151,7 +150,6 @@ func NewQueryDataHandler(config DataPluginConfiguration, queryResultTransformer
 		queryDataHandler.metricColumnTypes = config.MetricColumnTypes
 	}
 
-	// Create the xorm engine
 	engine, err := NewXormEngine(config.DriverName, config.ConnectionString)
 	if err != nil {
 		return nil, err
@@ -162,11 +160,6 @@ func NewQueryDataHandler(config DataPluginConfiguration, queryResultTransformer
 	engine.SetConnMaxLifetime(time.Duration(config.DSInfo.JsonData.ConnMaxLifetime) * time.Second)
 
 	queryDataHandler.engine = engine
-
-	// Create the xorm session
-	session := engine.NewSession()
-	queryDataHandler.session = session
-
 	return &queryDataHandler, nil
 }
 
@@ -277,7 +270,9 @@ func (e *DataSourceHandler) executeQuery(query backend.DataQuery, wg *sync.WaitG
 		return
 	}
 
-	db := e.session.DB()
+	session := e.engine.NewSession()
+	defer session.Close()
+	db := session.DB()
 
 	rows, err := db.QueryContext(queryContext, interpolatedQuery)
 	if err != nil {