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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 );
}
}
}
}