[8.x] Add isolation level configuration for Postgres connector (#40767)

* [8.x] Add isolation level configuration for Postgres connector

* formatting

Co-authored-by: Taylor Otwell <[email protected]>

Author: reziamini

src/Illuminate/Database/Connectors/PostgresConnector.php

@@ -33,6 +33,8 @@ public function connect(array $config)
             $this->getDsn($config), $config, $this->getOptions($config)
         );
 
+        $this->configureIsolationLevel($connection, $config);
+
         $this->configureEncoding($connection, $config);
 
         // Next, we will check to see if a timezone has been specified in this config
@@ -52,6 +54,20 @@ public function connect(array $config)
         return $connection;
     }
 
+    /**
+     * Set the connection transaction isolation level.
+     *
+     * @param  \PDO  $connection
+     * @param  array  $config
+     * @return void
+     */
+    protected function configureIsolationLevel($connection, array $config)
+    {
+        if (isset($config['isolation_level'])) {
+            $connection->prepare("set session characteristics as transaction isolation level {$config['isolation_level']}")->execute();
+        }
+    }
+
     /**
      * Set the connection character set and collation.
      *