[ticket/9685] Buffer posts for search indexing when using mssqlnative.

To have a generic solution there is now a sql_buffer_nested_transaction()
which indicates that the given SQL driver requires buffering to run a
transaction while iterating over another result set.

PHPBB3-9685

phpBB/includes/db/dbal.php

@@ -241,6 +241,16 @@ class dbal
 		return $this->_sql_like_expression('LIKE \'' . $this->sql_escape($expression) . '\'');
 	}
 
+	/**
+	* Returns whether results of a query need to be buffered to run a transaction while iterating over them.
+	*
+	* @return bool Whether buffering is required.
+	*/
+	function sql_buffer_nested_transaction()
+	{
+		return false;
+	}
+
 	/**
 	* SQL Transaction
 	* @access private

phpBB/includes/db/mssqlnative.php

@@ -258,6 +258,14 @@ class dbal_mssqlnative extends dbal
 		return ($this->sql_server_version) ? 'MSSQL<br />' . $this->sql_server_version : 'MSSQL';
 	}
 
+	/**
+	* {@inheritDoc}
+	*/
+	function sql_buffer_nested_transaction()
+	{
+		return true;
+	}
+
 	/**
 	* SQL Transaction
 	* @access private
@@ -628,7 +636,7 @@ class dbal_mssqlnative extends dbal
 			return false;
 		}
 	}
-	
+
 	/**
 	* Allows setting mssqlnative specific query options passed to sqlsrv_query as 4th parameter.
 	*/