New maintenance script to recalculate category membership counts

The category membership counts stored in the category table have a habit of
drifting away from the actual number of pages in the category. This script
identifies incorrectly-counted categories by performing a SELECT on the
replica DB, then querying master for up-to-date counts and updating the
category rows with those counts.

It's possible that a LinksUpdate job will be in progress while this script
is run. LinksUpdate does categorylinks INSERTs and category UPDATEs in
separate transactions, and our count might occur in between, leading to
category values that are slightly off. But since we are only updating
categories with already incorrect counts, we are not making the situation
any worse than it already was.

The script runs reasonably quickly on all but the very largest wikis.

Bug: T18765
Change-Id: I555f068fbf3aee20a7775d5532781f421f706346

diff --git a/autoload.php b/autoload.php
index 7ed08df..d7624fb 100644 (file)
--- a/autoload.php
+++ b/autoload.php
@@ -1167,6 +1167,7 @@ $wgAutoloadLocalClasses = [
        'RecentChange' => __DIR__ . '/includes/changes/RecentChange.php',
        'RecentChangesUpdateJob' => __DIR__ . '/includes/jobqueue/jobs/RecentChangesUpdateJob.php',
        'RecompressTracked' => __DIR__ . '/maintenance/storage/recompressTracked.php',
+       'RecountCategories' => __DIR__ . '/maintenance/recountCategories.php',
        'RedirectSpecialArticle' => __DIR__ . '/includes/specialpage/RedirectSpecialPage.php',
        'RedirectSpecialPage' => __DIR__ . '/includes/specialpage/RedirectSpecialPage.php',
        'RedisBagOStuff' => __DIR__ . '/includes/libs/objectcache/RedisBagOStuff.php',

diff --git a/maintenance/recountCategories.php b/maintenance/recountCategories.php
new file mode 100644 (file)
index 0000000..a4bfa98
--- /dev/null
+++ b/maintenance/recountCategories.php
@@ -0,0 +1,172 @@
+<?php
+/**
+ * Refreshes category counts.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ * http://www.gnu.org/copyleft/gpl.html
+ *
+ * @file
+ * @ingroup Maintenance
+ */
+
+require_once __DIR__ . '/Maintenance.php';
+
+use MediaWiki\MediaWikiServices;
+
+/**
+ * Maintenance script that refreshes category membership counts in the category
+ * table.
+ *
+ * (The populateCategory.php script will also recalculate counts, but
+ * recountCategories only updates rows that need to be updated, making it more
+ * efficient.)
+ *
+ * @ingroup Maintenance
+ */
+class RecountCategories extends Maintenance {
+       public function __construct() {
+               parent::__construct();
+               $this->addDescription( <<<'TEXT'
+This script refreshes the category membership counts stored in the category
+table. As time passes, these counts often drift from the actual number of
+category members. The script identifies rows where the value in the category
+table does not match the number of categorylinks rows for that category, and
+updates the category table accordingly.
+
+To fully refresh the data in the category table, you need to run this script
+three times: once in each mode. Alternatively, just one mode can be run if
+required.
+TEXT
+               );
+               $this->addOption(
+                       'mode',
+                       '(REQUIRED) Which category count column to recompute: "pages", "subcats" or "files".',
+                       true,
+                       true
+               );
+               $this->addOption(
+                       'begin',
+                       'Only recount categories with cat_id greater than the given value',
+                       false,
+                       true
+               );
+               $this->addOption(
+                       'throttle',
+                       'Wait this many milliseconds after each batch. Default: 0',
+                       false,
+                       true
+               );
+
+               $this->setBatchSize( 500 );
+       }
+
+       public function execute() {
+               $this->mode = $this->getOption( 'mode' );
+               if ( !in_array( $this->mode, [ 'pages', 'subcats', 'files' ] ) ) {
+                       $this->error( 'Please specify a valid mode: one of "pages", "subcats" or "files".', 1 );
+               }
+
+               $this->minimumId = intval( $this->getOption( 'begin', 0 ) );
+
+               // do the work, batch by batch
+               $affectedRows = 0;
+               while ( ( $result = $this->doWork() ) !== false ) {
+                       $affectedRows += $result;
+                       usleep( $this->getOption( 'throttle', 0 ) * 1000 );
+               }
+
+               $this->output( "Done! Updated the {$this->mode} counts of $affectedRows categories.\n" .
+                       "Now run the script using the other --mode options if you haven't already.\n" );
+               if ( $this->mode === 'pages' ) {
+                       $this->output(
+                               "Also run 'php cleanupEmptyCategories.php --mode remove' to remove empty,\n" .
+                               "nonexistent categories from the category table.\n\n" );
+               }
+       }
+
+       protected function doWork() {
+               $this->output( "Finding up to {$this->mBatchSize} drifted rows " .
+                       "starting at cat_id {$this->minimumId}...\n" );
+
+               $countingConds = [ 'cl_to = cat_title' ];
+               if ( $this->mode === 'subcats' ) {
+                       $countingConds['cl_type'] = 'subcat';
+               } elseif ( $this->mode === 'files' ) {
+                       $countingConds['cl_type'] = 'file';
+               }
+
+               $dbr = $this->getDB( DB_REPLICA, 'vslow' );
+               $countingSubquery = $dbr->selectSQLText( 'categorylinks',
+                       'COUNT(*)',
+                       $countingConds,
+                       __METHOD__ );
+
+               // First, let's find out which categories have drifted and need to be updated.
+               // The query counts the categorylinks for each category on the replica DB,
+               // but this data can't be used for updating the master, so we don't include it
+               // in the results.
+               $idsToUpdate = $dbr->selectFieldValues( 'category',
+                       'cat_id',
+                       [
+                               'cat_id > ' . $this->minimumId,
+                               "cat_{$this->mode} != ($countingSubquery)"
+                       ],
+                       __METHOD__,
+                       [ 'LIMIT' => $this->mBatchSize ]
+               );
+               if ( !$idsToUpdate ) {
+                       return false;
+               }
+               $this->output( "Updating cat_{$this->mode} field on " .
+                       count( $idsToUpdate ) . " rows...\n" );
+
+               // In the next batch, start where this query left off. The rows selected
+               // in this iteration shouldn't be selected again after being updated, but
+               // we still keep track of where we are up to, as extra protection against
+               // infinite loops.
+               $this->minimumId = end( $idsToUpdate );
+
+               // Now, on master, find the correct counts for these categories.
+               $dbw = $this->getDB( DB_MASTER );
+               $res = $dbw->select( 'category',
+                       [ 'cat_id', 'count' => "($countingSubquery)" ],
+                       [ 'cat_id' => $idsToUpdate ],
+                       __METHOD__ );
+
+               // Update the category counts on the rows we just identified.
+               // This logic is equivalent to Category::refreshCounts, except here, we
+               // don't remove rows when cat_pages is zero and the category description page
+               // doesn't exist - instead we print a suggestion to run
+               // cleanupEmptyCategories.php.
+               $affectedRows = 0;
+               foreach ( $res as $row ) {
+                       $dbw->update( 'category',
+                               [ "cat_{$this->mode}" => $row->count ],
+                               [
+                                       'cat_id' => $row->cat_id,
+                                       "cat_{$this->mode} != {$row->count}",
+                               ],
+                               __METHOD__ );
+                       $affectedRows += $dbw->affectedRows();
+               }
+
+               MediaWikiServices::getInstance()->getDBLoadBalancerFactory()->waitForReplication();
+
+               return $affectedRows;
+       }
+}
+
+$maintClass = 'RecountCategories';
+require_once RUN_MAINTENANCE_IF_MAIN;