[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/acp/acp_search.php

@@ -392,7 +392,18 @@ class acp_search
 									AND post_id <= ' . (int) ($post_counter + $this->batch_size);
 							$result = $db->sql_query($sql);
 
-							while ($row = $db->sql_fetchrow($result))
+							$buffer = $db->sql_buffer_nested_transactions();
+
+							if ($buffer)
+							{
+								$rows = $db->sql_fetchrowset($result);
+								$rows[] = false; // indicate end of array for while loop below
+
+								$db->sql_freeresult($result);
+							}
+
+							$i = 0;
+							while ($row = ($buffer ? $rows[$i++] : $db->sql_fetchrow($result)))
 							{
 								// Indexing enabled for this forum or global announcement?
 								// Global announcements get indexed by default.
@@ -402,7 +413,10 @@ class acp_search
 								}
 								$row_count++;
 							}
+							if (!$buffer)
+							{
 								$db->sql_freeresult($result);
+							}
 
 							$post_counter += $this->batch_size;
 						}

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