Unbuffered queries result freeing & error handling

Puts result set ownership back into producer, and tries to restore the
database buffering upon exceptions during dumps

Change-Id: Ie3e2b5b39cc6cef25a0021694e7a53a92b1dff5b

diff --git a/includes/Export.php b/includes/Export.php
index 0d1aeef..24daa09 100644 (file)
--- a/includes/Export.php
+++ b/includes/Export.php
@@ -209,9 +209,6 @@ class WikiExporter {
                wfProfileIn( __METHOD__ );
                # For logging dumps...
                if ( $this->history & self::LOGS ) {
-                       if ( $this->buffer == WikiExporter::STREAM ) {
-                               $prev = $this->db->bufferResults( false );
-                       }
                        $where = array( 'user_id = log_user' );
                        # Hide private logs
                        $hideLogs = LogEventsList::getExcludeClause( $this->db );
@@ -220,16 +217,49 @@ class WikiExporter {
                        if ( $cond ) $where[] = $cond;
                        # Get logging table name for logging.* clause
                        $logging = $this->db->tableName( 'logging' );
-                       $result = $this->db->select( array( 'logging', 'user' ),
-                               array( "{$logging}.*", 'user_name' ), // grab the user name
-                               $where,
-                               __METHOD__,
-                               array( 'ORDER BY' => 'log_id', 'USE INDEX' => array( 'logging' => 'PRIMARY' ) )
-                       );
-                       $wrapper = $this->db->resultObject( $result );
-                       $this->outputLogStream( $wrapper );
+
                        if ( $this->buffer == WikiExporter::STREAM ) {
-                               $this->db->bufferResults( $prev );
+                               $prev = $this->db->bufferResults( false );
+                       }
+                       $wrapper = null; // Assuring $wrapper is not undefined, if exception occurs early
+                       try {
+                               $result = $this->db->select( array( 'logging', 'user' ),
+                                       array( "{$logging}.*", 'user_name' ), // grab the user name
+                                       $where,
+                                       __METHOD__,
+                                       array( 'ORDER BY' => 'log_id', 'USE INDEX' => array( 'logging' => 'PRIMARY' ) )
+                               );
+                               $wrapper = $this->db->resultObject( $result );
+                               $this->outputLogStream( $wrapper );
+                               if ( $this->buffer == WikiExporter::STREAM ) {
+                                       $this->db->bufferResults( $prev );
+                               }
+                       } catch ( Exception $e ) {
+                               // Throwing the exception does not reliably free the resultset, and
+                               // would also leave the connection in unbuffered mode.
+
+                               // Freeing result
+                               try {
+                                       if ( $wrapper ) {
+                                               $wrapper->free();
+                                       }
+                               } catch ( Exception $e2 ) {
+                                       // Already in panic mode -> ignoring $e2 as $e has
+                                       // higher priority
+                               }
+
+                               // Putting database back in previous buffer mode
+                               try {
+                                       if ( $this->buffer == WikiExporter::STREAM ) {
+                                               $this->db->bufferResults( $prev );
+                                       }
+                               } catch ( Exception $e2 ) {
+                                       // Already in panic mode -> ignoring $e2 as $e has
+                                       // higher priority
+                               }
+
+                               // Inform caller about problem
+                               throw $e;
                        }
                # For page dumps...
                } else {
@@ -300,17 +330,46 @@ class WikiExporter {
                                $prev = $this->db->bufferResults( false );
                        }
 
-                       wfRunHooks( 'ModifyExportQuery',
+                       $wrapper = null; // Assuring $wrapper is not undefined, if exception occurs early
+                       try {
+                               wfRunHooks( 'ModifyExportQuery',
                                                array( $this->db, &$tables, &$cond, &$opts, &$join ) );
 
-                       # Do the query!
-                       $result = $this->db->select( $tables, '*', $cond, __METHOD__, $opts, $join );
-                       $wrapper = $this->db->resultObject( $result );
-                       # Output dump results
-                       $this->outputPageStream( $wrapper );
+                               # Do the query!
+                               $result = $this->db->select( $tables, '*', $cond, __METHOD__, $opts, $join );
+                               $wrapper = $this->db->resultObject( $result );
+                               # Output dump results
+                               $this->outputPageStream( $wrapper );
 
-                       if ( $this->buffer == WikiExporter::STREAM ) {
-                               $this->db->bufferResults( $prev );
+                               if ( $this->buffer == WikiExporter::STREAM ) {
+                                       $this->db->bufferResults( $prev );
+                               }
+                       } catch ( Exception $e ) {
+                               // Throwing the exception does not reliably free the resultset, and
+                               // would also leave the connection in unbuffered mode.
+
+                               // Freeing result
+                               try {
+                                       if ( $wrapper ) {
+                                               $wrapper->free();
+                                       }
+                               } catch ( Exception $e2 ) {
+                                       // Already in panic mode -> ignoring $e2 as $e has
+                                       // higher priority
+                               }
+
+                               // Putting database back in previous buffer mode
+                               try {
+                                       if ( $this->buffer == WikiExporter::STREAM ) {
+                                               $this->db->bufferResults( $prev );
+                                       }
+                               } catch ( Exception $e2 ) {
+                                       // Already in panic mode -> ignoring $e2 as $e has
+                                       // higher priority
+                               }
+
+                               // Inform caller about problem
+                               throw $e;
                        }
                }
                wfProfileOut( __METHOD__ );
@@ -321,7 +380,7 @@ class WikiExporter {
         * The result set should be sorted/grouped by page to avoid duplicate
         * page records in the output.
         *
-        * The result set will be freed once complete. Should be safe for
+        * Should be safe for
         * streaming (non-buffered) queries, as long as it was made on a
         * separate database connection not managed by LoadBalancer; some
         * blob storage types will make queries to pull source data.