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<?php
/**
* Class to invalidate the HTML cache of all the pages linking to a given title.
* Small numbers of links will be done immediately, large numbers are pushed onto
* the job 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 Cache
*/
class HTMLCacheUpdate
{
/**
* @var Title
*/
public $mTitle;
public $mTable, $mPrefix, $mStart, $mEnd;
public $mRowsPerJob, $mRowsPerQuery;
function __construct( $titleTo, $table, $start = false, $end = false ) {
global $wgUpdateRowsPerJob, $wgUpdateRowsPerQuery;
$this->mTitle = $titleTo;
$this->mTable = $table;
$this->mStart = $start;
$this->mEnd = $end;
$this->mRowsPerJob = $wgUpdateRowsPerJob;
$this->mRowsPerQuery = $wgUpdateRowsPerQuery;
$this->mCache = $this->mTitle->getBacklinkCache();
}
public function doUpdate() {
if ( $this->mStart || $this->mEnd ) {
$this->doPartialUpdate();
return;
}
# Get an estimate of the number of rows from the BacklinkCache
$numRows = $this->mCache->getNumLinks( $this->mTable );
if ( $numRows > $this->mRowsPerJob * 2 ) {
# Do fast cached partition
$this->insertJobs();
} else {
# Get the links from the DB
$titleArray = $this->mCache->getLinks( $this->mTable );
# Check if the row count estimate was correct
if ( $titleArray->count() > $this->mRowsPerJob * 2 ) {
# Not correct, do accurate partition
wfDebug( __METHOD__.": row count estimate was incorrect, repartitioning\n" );
$this->insertJobsFromTitles( $titleArray );
} else {
$this->invalidateTitles( $titleArray );
}
}
}
/**
* Update some of the backlinks, defined by a page ID range
*/
protected function doPartialUpdate() {
$titleArray = $this->mCache->getLinks( $this->mTable, $this->mStart, $this->mEnd );
if ( $titleArray->count() <= $this->mRowsPerJob * 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 );
}
}
/**
* Partition the current range given by $this->mStart and $this->mEnd,
* using a pre-calculated title array which gives the links in that range.
* Queue the resulting jobs.
*
* @param $titleArray array
*/
protected function insertJobsFromTitles( $titleArray ) {
# 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->mStart; # 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->mRowsPerJob ) {
# Add a job up to but not including the current ID
$params = array(
'table' => $this->mTable,
'start' => $start,
'end' => $id - 1
);
$jobs[] = new HTMLCacheUpdateJob( $this->mTitle, $params );
$start = $id;
$numTitles = 0;
}
$numTitles++;
}
# Last job
$params = array(
'table' => $this->mTable,
'start' => $start,
'end' => $this->mEnd
);
$jobs[] = new HTMLCacheUpdateJob( $this->mTitle, $params );
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 );
return;
}
Job::batchInsert( $jobs );
}
protected function insertJobs() {
$batches = $this->mCache->partition( $this->mTable, $this->mRowsPerJob );
if ( !$batches ) {
return;
}
$jobs = array();
foreach ( $batches as $batch ) {
$params = array(
'table' => $this->mTable,
'start' => $batch[0],
'end' => $batch[1],
);
$jobs[] = new HTMLCacheUpdateJob( $this->mTitle, $params );
}
Job::batchInsert( $jobs );
}
/**
* Invalidate an array (or iterator) of Title objects, right now
*/
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;
}
# Update page_touched
$batches = array_chunk( $ids, $this->mRowsPerQuery );
foreach ( $batches as $batch ) {
$dbw->update( 'page',
array( 'page_touched' => $timestamp ),
array( 'page_id IN (' . $dbw->makeList( $batch ) . ')' ),
__METHOD__
);
}
# Update squid
if ( $wgUseSquid ) {
$u = SquidUpdate::newFromTitles( $titleArray );
$u->doUpdate();
}
# Update file cache
if ( $wgUseFileCache ) {
foreach ( $titleArray as $title ) {
HTMLFileCache::clearFileCache( $title );
}
}
}
}
/**
* Job wrapper for HTMLCacheUpdate. Gets run whenever a related
* job gets called from the queue.
*
* @ingroup JobQueue
*/
class HTMLCacheUpdateJob extends Job {
var $table, $start, $end;
/**
* Construct a job
* @param $title Title: the title linked to
* @param $params Array: job parameters (table, start and end page_ids)
* @param $id Integer: job id
*/
function __construct( $title, $params, $id = 0 ) {
parent::__construct( 'htmlCacheUpdate', $title, $params, $id );
$this->table = $params['table'];
$this->start = $params['start'];
$this->end = $params['end'];
}
public function run() {
$update = new HTMLCacheUpdate( $this->title, $this->table, $this->start, $this->end );
$update->doUpdate();
return true;
}
}
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