1 files changed, 254 insertions, 0 deletions
diff --git a/includes/job/jobs/HTMLCacheUpdateJob.php b/includes/job/jobs/HTMLCacheUpdateJob.php
new file mode 100644
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+++ b/includes/job/jobs/HTMLCacheUpdateJob.php
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+<?php
+/**
+ * HTML cache invalidation of all pages linking to a given title.
+ *
+ * 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 Cache
+ */
+
+/**
+ * Job wrapper for HTMLCacheUpdate. Gets run whenever a related
+ * job gets called from the queue.
+ *
+ * This class is designed to work efficiently with small numbers of links, and
+ * to work reasonably well with up to ~10^5 links. Above ~10^6 links, the memory
+ * and time requirements of loading all backlinked IDs in doUpdate() might become
+ * prohibitive. The requirements measured at Wikimedia are approximately:
+ *
+ *   memory: 48 bytes per row
+ *   time: 16us per row for the query plus processing
+ *
+ * The reason this query is done is to support partitioning of the job
+ * by backlinked ID. The memory issue could be allieviated by doing this query in
+ * batches, but of course LIMIT with an offset is inefficient on the DB side.
+ *
+ * The class is nevertheless a vast improvement on the previous method of using
+ * File::getLinksTo() and Title::touchArray(), which uses about 2KB of memory per
+ * link.
+ *
+ * @ingroup JobQueue
+ */
+class HTMLCacheUpdateJob extends Job {
+	/** @var BacklinkCache */
+	protected $blCache;
+
+	protected $rowsPerJob, $rowsPerQuery;
+
+	/**
+	 * Construct a job
+	 * @param $title Title: the title linked to
+	 * @param array $params job parameters (table, start and end page_ids)
+	 * @param $id Integer: job id
+	 */
+	function __construct( $title, $params, $id = 0 ) {
+		global $wgUpdateRowsPerJob, $wgUpdateRowsPerQuery;
+
+		parent::__construct( 'htmlCacheUpdate', $title, $params, $id );
+
+		$this->rowsPerJob = $wgUpdateRowsPerJob;
+		$this->rowsPerQuery = $wgUpdateRowsPerQuery;
+		$this->blCache = $title->getBacklinkCache();
+	}
+
+	public function run() {
+		if ( isset( $this->params['start'] ) && isset( $this->params['end'] ) ) {
+			# This is hit when a job is actually performed
+			return $this->doPartialUpdate();
+		} else {
+			# This is hit when the jobs have to be inserted
+			return $this->doFullUpdate();
+		}
+	}
+
+	/**
+	 * Update all of the backlinks
+	 */
+	protected function doFullUpdate() {
+		# Get an estimate of the number of rows from the BacklinkCache
+		$numRows = $this->blCache->getNumLinks( $this->params['table'] );
+		if ( $numRows > $this->rowsPerJob * 2 ) {
+			# Do fast cached partition
+			$this->insertPartitionJobs();
+		} else {
+			# Get the links from the DB
+			$titleArray = $this->blCache->getLinks( $this->params['table'] );
+			# Check if the row count estimate was correct
+			if ( $titleArray->count() > $this->rowsPerJob * 2 ) {
+				# Not correct, do accurate partition
+				wfDebug( __METHOD__.": row count estimate was incorrect, repartitioning\n" );
+				$this->insertJobsFromTitles( $titleArray );
+			} else {
+				$this->invalidateTitles( $titleArray ); // just do the query
+			}
+		}
+		return true;
+	}
+
+	/**
+	 * Update some of the backlinks, defined by a page ID range
+	 */
+	protected function doPartialUpdate() {
+		$titleArray = $this->blCache->getLinks(
+			$this->params['table'], $this->params['start'], $this->params['end'] );
+		if ( $titleArray->count() <= $this->rowsPerJob * 2 ) {
+			# This partition is small enough, do the update
+			$this->invalidateTitles( $titleArray );
+		} else {
+			# Partitioning was excessively inaccurate. Divide the job further.
+			# This can occur when a large number of links are added in a short
+			# period of time, say by updating a heavily-used template.
+			$this->insertJobsFromTitles( $titleArray );
+		}
+		return true;
+	}
+
+	/**
+	 * Partition the current range given by $this->params['start'] and $this->params['end'],
+	 * using a pre-calculated title array which gives the links in that range.
+	 * Queue the resulting jobs.
+	 *
+	 * @param $titleArray array
+	 * @param $rootJobParams array
+	 * @return void
+	 */
+	protected function insertJobsFromTitles( $titleArray, $rootJobParams = array() ) {
+		// Carry over any "root job" information
+		$rootJobParams = $this->getRootJobParams();
+		# We make subpartitions in the sense that the start of the first job
+		# will be the start of the parent partition, and the end of the last
+		# job will be the end of the parent partition.
+		$jobs = array();
+		$start = $this->params['start']; # start of the current job
+		$numTitles = 0;
+		foreach ( $titleArray as $title ) {
+			$id = $title->getArticleID();
+			# $numTitles is now the number of titles in the current job not
+			# including the current ID
+			if ( $numTitles >= $this->rowsPerJob ) {
+				# Add a job up to but not including the current ID
+				$jobs[] = new HTMLCacheUpdateJob( $this->title,
+					array(
+						'table' => $this->params['table'],
+						'start' => $start,
+						'end'   => $id - 1
+					) + $rootJobParams // carry over information for de-duplication
+				);
+				$start = $id;
+				$numTitles = 0;
+			}
+			$numTitles++;
+		}
+		# Last job
+		$jobs[] = new HTMLCacheUpdateJob( $this->title,
+			array(
+				'table' => $this->params['table'],
+				'start' => $start,
+				'end'   => $this->params['end']
+			) + $rootJobParams // carry over information for de-duplication
+		);
+		wfDebug( __METHOD__.": repartitioning into " . count( $jobs ) . " jobs\n" );
+
+		if ( count( $jobs ) < 2 ) {
+			# I don't think this is possible at present, but handling this case
+			# makes the code a bit more robust against future code updates and
+			# avoids a potential infinite loop of repartitioning
+			wfDebug( __METHOD__.": repartitioning failed!\n" );
+			$this->invalidateTitles( $titleArray );
+		} else {
+			JobQueueGroup::singleton()->push( $jobs );
+		}
+	}
+
+	/**
+	 * @param $rootJobParams array
+	 * @return void
+	 */
+	protected function insertPartitionJobs( $rootJobParams = array() ) {
+		// Carry over any "root job" information
+		$rootJobParams = $this->getRootJobParams();
+
+		$batches = $this->blCache->partition( $this->params['table'], $this->rowsPerJob );
+		if ( !count( $batches ) ) {
+			return; // no jobs to insert
+		}
+
+		$jobs = array();
+		foreach ( $batches as $batch ) {
+			list( $start, $end ) = $batch;
+			$jobs[] = new HTMLCacheUpdateJob( $this->title,
+				array(
+					'table' => $this->params['table'],
+					'start' => $start,
+					'end'   => $end,
+				) + $rootJobParams // carry over information for de-duplication
+			);
+		}
+
+		JobQueueGroup::singleton()->push( $jobs );
+	}
+
+	/**
+	 * Invalidate an array (or iterator) of Title objects, right now
+	 * @param $titleArray array
+	 */
+	protected function invalidateTitles( $titleArray ) {
+		global $wgUseFileCache, $wgUseSquid;
+
+		$dbw = wfGetDB( DB_MASTER );
+		$timestamp = $dbw->timestamp();
+
+		# Get all IDs in this query into an array
+		$ids = array();
+		foreach ( $titleArray as $title ) {
+			$ids[] = $title->getArticleID();
+		}
+
+		if ( !$ids ) {
+			return;
+		}
+
+		# Don't invalidated pages that were already invalidated
+		$touchedCond = isset( $this->params['rootJobTimestamp'] )
+			? array( "page_touched < " .
+				$dbw->addQuotes( $dbw->timestamp( $this->params['rootJobTimestamp'] ) ) )
+			: array();
+
+		# Update page_touched
+		$batches = array_chunk( $ids, $this->rowsPerQuery );
+		foreach ( $batches as $batch ) {
+			$dbw->update( 'page',
+				array( 'page_touched' => $timestamp ),
+				array( 'page_id' => $batch ) + $touchedCond,
+				__METHOD__
+			);
+		}
+
+		# Update squid
+		if ( $wgUseSquid ) {
+			$u = SquidUpdate::newFromTitles( $titleArray );
+			$u->doUpdate();
+		}
+
+		# Update file cache
+		if  ( $wgUseFileCache ) {
+			foreach ( $titleArray as $title ) {
+				HTMLFileCache::clearFileCache( $title );
+			}
+		}
+	}
+}