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<?php
/**
* Class for fetching backlink lists, approximate backlink counts and
* partitions.
*
* 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
* @author Tim Starling
* @author Aaron Schulz
* @copyright © 2009, Tim Starling, Domas Mituzas
* @copyright © 2010, Max Sem
* @copyright © 2011, Antoine Musso
*/
/**
* Class for fetching backlink lists, approximate backlink counts and
* partitions. This is a shared cache.
*
* Instances of this class should typically be fetched with the method
* $title->getBacklinkCache().
*
* Ideally you should only get your backlinks from here when you think
* there is some advantage in caching them. Otherwise it's just a waste
* of memory.
*
* Introduced by r47317
*/
class BacklinkCache {
/** @var BacklinkCache */
protected static $instance;
/**
* Multi dimensions array representing batches. Keys are:
* > (string) links table name
* > (int) batch size
* > 'numRows' : Number of rows for this link table
* > 'batches' : array( $start, $end )
*
* @see BacklinkCache::partitionResult()
*
* Cleared with BacklinkCache::clear()
* @var array[]
*/
protected $partitionCache = [];
/**
* Contains the whole links from a database result.
* This is raw data that will be partitioned in $partitionCache
*
* Initialized with BacklinkCache::getLinks()
* Cleared with BacklinkCache::clear()
* @var ResultWrapper[]
*/
protected $fullResultCache = [];
/**
* Local copy of a database object.
*
* Accessor: BacklinkCache::getDB()
* Mutator : BacklinkCache::setDB()
* Cleared with BacklinkCache::clear()
*/
protected $db;
/**
* Local copy of a Title object
*/
protected $title;
const CACHE_EXPIRY = 3600;
/**
* Create a new BacklinkCache
*
* @param Title $title : Title object to create a backlink cache for
*/
public function __construct( Title $title ) {
$this->title = $title;
}
/**
* Create a new BacklinkCache or reuse any existing one.
* Currently, only one cache instance can exist; callers that
* need multiple backlink cache objects should keep them in scope.
*
* @param Title $title Title object to get a backlink cache for
* @return BacklinkCache
*/
public static function get( Title $title ) {
if ( !self::$instance || !self::$instance->title->equals( $title ) ) {
self::$instance = new self( $title );
}
return self::$instance;
}
/**
* Serialization handler, diasallows to serialize the database to prevent
* failures after this class is deserialized from cache with dead DB
* connection.
*
* @return array
*/
function __sleep() {
return [ 'partitionCache', 'fullResultCache', 'title' ];
}
/**
* Clear locally stored data and database object.
*/
public function clear() {
$this->partitionCache = [];
$this->fullResultCache = [];
unset( $this->db );
}
/**
* Set the Database object to use
*
* @param IDatabase $db
*/
public function setDB( $db ) {
$this->db = $db;
}
/**
* Get the slave connection to the database
* When non existing, will initialize the connection.
* @return DatabaseBase
*/
protected function getDB() {
if ( !isset( $this->db ) ) {
$this->db = wfGetDB( DB_SLAVE );
}
return $this->db;
}
/**
* Get the backlinks for a given table. Cached in process memory only.
* @param string $table
* @param int|bool $startId
* @param int|bool $endId
* @param int $max
* @return TitleArrayFromResult
*/
public function getLinks( $table, $startId = false, $endId = false, $max = INF ) {
return TitleArray::newFromResult( $this->queryLinks( $table, $startId, $endId, $max ) );
}
/**
* Get the backlinks for a given table. Cached in process memory only.
* @param string $table
* @param int|bool $startId
* @param int|bool $endId
* @param int $max
* @param string $select 'all' or 'ids'
* @return ResultWrapper
*/
protected function queryLinks( $table, $startId, $endId, $max, $select = 'all' ) {
$fromField = $this->getPrefix( $table ) . '_from';
if ( !$startId && !$endId && is_infinite( $max )
&& isset( $this->fullResultCache[$table] )
) {
wfDebug( __METHOD__ . ": got results from cache\n" );
$res = $this->fullResultCache[$table];
} else {
wfDebug( __METHOD__ . ": got results from DB\n" );
$conds = $this->getConditions( $table );
// Use the from field in the condition rather than the joined page_id,
// because databases are stupid and don't necessarily propagate indexes.
if ( $startId ) {
$conds[] = "$fromField >= " . intval( $startId );
}
if ( $endId ) {
$conds[] = "$fromField <= " . intval( $endId );
}
$options = [ 'ORDER BY' => $fromField ];
if ( is_finite( $max ) && $max > 0 ) {
$options['LIMIT'] = $max;
}
if ( $select === 'ids' ) {
// Just select from the backlink table and ignore the page JOIN
$res = $this->getDB()->select(
$table,
[ $this->getPrefix( $table ) . '_from AS page_id' ],
array_filter( $conds, function ( $clause ) { // kind of janky
return !preg_match( '/(\b|=)page_id(\b|=)/', $clause );
} ),
__METHOD__,
$options
);
} else {
// Select from the backlink table and JOIN with page title information
$res = $this->getDB()->select(
[ $table, 'page' ],
[ 'page_namespace', 'page_title', 'page_id' ],
$conds,
__METHOD__,
array_merge( [ 'STRAIGHT_JOIN' ], $options )
);
}
if ( $select === 'all' && !$startId && !$endId && $res->numRows() < $max ) {
// The full results fit within the limit, so cache them
$this->fullResultCache[$table] = $res;
} else {
wfDebug( __METHOD__ . ": results from DB were uncacheable\n" );
}
}
return $res;
}
/**
* Get the field name prefix for a given table
* @param string $table
* @throws MWException
* @return null|string
*/
protected function getPrefix( $table ) {
static $prefixes = [
'pagelinks' => 'pl',
'imagelinks' => 'il',
'categorylinks' => 'cl',
'templatelinks' => 'tl',
'redirect' => 'rd',
];
if ( isset( $prefixes[$table] ) ) {
return $prefixes[$table];
} else {
$prefix = null;
Hooks::run( 'BacklinkCacheGetPrefix', [ $table, &$prefix ] );
if ( $prefix ) {
return $prefix;
} else {
throw new MWException( "Invalid table \"$table\" in " . __CLASS__ );
}
}
}
/**
* Get the SQL condition array for selecting backlinks, with a join
* on the page table.
* @param string $table
* @throws MWException
* @return array|null
*/
protected function getConditions( $table ) {
$prefix = $this->getPrefix( $table );
switch ( $table ) {
case 'pagelinks':
case 'templatelinks':
$conds = [
"{$prefix}_namespace" => $this->title->getNamespace(),
"{$prefix}_title" => $this->title->getDBkey(),
"page_id={$prefix}_from"
];
break;
case 'redirect':
$conds = [
"{$prefix}_namespace" => $this->title->getNamespace(),
"{$prefix}_title" => $this->title->getDBkey(),
$this->getDB()->makeList( [
"{$prefix}_interwiki" => '',
"{$prefix}_interwiki IS NULL",
], LIST_OR ),
"page_id={$prefix}_from"
];
break;
case 'imagelinks':
case 'categorylinks':
$conds = [
"{$prefix}_to" => $this->title->getDBkey(),
"page_id={$prefix}_from"
];
break;
default:
$conds = null;
Hooks::run( 'BacklinkCacheGetConditions', [ $table, $this->title, &$conds ] );
if ( !$conds ) {
throw new MWException( "Invalid table \"$table\" in " . __CLASS__ );
}
}
return $conds;
}
/**
* Check if there are any backlinks
* @param string $table
* @return bool
*/
public function hasLinks( $table ) {
return ( $this->getNumLinks( $table, 1 ) > 0 );
}
/**
* Get the approximate number of backlinks
* @param string $table
* @param int $max Only count up to this many backlinks
* @return int
*/
public function getNumLinks( $table, $max = INF ) {
global $wgUpdateRowsPerJob;
$cache = ObjectCache::getMainWANInstance();
// 1) try partition cache ...
if ( isset( $this->partitionCache[$table] ) ) {
$entry = reset( $this->partitionCache[$table] );
return min( $max, $entry['numRows'] );
}
// 2) ... then try full result cache ...
if ( isset( $this->fullResultCache[$table] ) ) {
return min( $max, $this->fullResultCache[$table]->numRows() );
}
$memcKey = wfMemcKey( 'numbacklinks', md5( $this->title->getPrefixedDBkey() ), $table );
// 3) ... fallback to memcached ...
$count = $cache->get( $memcKey );
if ( $count ) {
return min( $max, $count );
}
// 4) fetch from the database ...
if ( is_infinite( $max ) ) { // no limit at all
// Use partition() since it will batch the query and skip the JOIN.
// Use $wgUpdateRowsPerJob just to encourage cache reuse for jobs.
$this->partition( $table, $wgUpdateRowsPerJob ); // updates $this->partitionCache
return $this->partitionCache[$table][$wgUpdateRowsPerJob]['numRows'];
} else { // probably some sane limit
// Fetch the full title info, since the caller will likely need it next
$count = $this->getLinks( $table, false, false, $max )->count();
if ( $count < $max ) { // full count
$cache->set( $memcKey, $count, self::CACHE_EXPIRY );
}
}
return min( $max, $count );
}
/**
* Partition the backlinks into batches.
* Returns an array giving the start and end of each range. The first
* batch has a start of false, and the last batch has an end of false.
*
* @param string $table The links table name
* @param int $batchSize
* @return array
*/
public function partition( $table, $batchSize ) {
// 1) try partition cache ...
if ( isset( $this->partitionCache[$table][$batchSize] ) ) {
wfDebug( __METHOD__ . ": got from partition cache\n" );
return $this->partitionCache[$table][$batchSize]['batches'];
}
$cache = ObjectCache::getMainWANInstance();
$this->partitionCache[$table][$batchSize] = false;
$cacheEntry =& $this->partitionCache[$table][$batchSize];
// 2) ... then try full result cache ...
if ( isset( $this->fullResultCache[$table] ) ) {
$cacheEntry = $this->partitionResult( $this->fullResultCache[$table], $batchSize );
wfDebug( __METHOD__ . ": got from full result cache\n" );
return $cacheEntry['batches'];
}
$memcKey = wfMemcKey(
'backlinks',
md5( $this->title->getPrefixedDBkey() ),
$table,
$batchSize
);
// 3) ... fallback to memcached ...
$memcValue = $cache->get( $memcKey );
if ( is_array( $memcValue ) ) {
$cacheEntry = $memcValue;
wfDebug( __METHOD__ . ": got from memcached $memcKey\n" );
return $cacheEntry['batches'];
}
// 4) ... finally fetch from the slow database :(
$cacheEntry = [ 'numRows' => 0, 'batches' => [] ]; // final result
// Do the selects in batches to avoid client-side OOMs (bug 43452).
// Use a LIMIT that plays well with $batchSize to keep equal sized partitions.
$selectSize = max( $batchSize, 200000 - ( 200000 % $batchSize ) );
$start = false;
do {
$res = $this->queryLinks( $table, $start, false, $selectSize, 'ids' );
$partitions = $this->partitionResult( $res, $batchSize, false );
// Merge the link count and range partitions for this chunk
$cacheEntry['numRows'] += $partitions['numRows'];
$cacheEntry['batches'] = array_merge( $cacheEntry['batches'], $partitions['batches'] );
if ( count( $partitions['batches'] ) ) {
list( , $lEnd ) = end( $partitions['batches'] );
$start = $lEnd + 1; // pick up after this inclusive range
}
} while ( $partitions['numRows'] >= $selectSize );
// Make sure the first range has start=false and the last one has end=false
if ( count( $cacheEntry['batches'] ) ) {
$cacheEntry['batches'][0][0] = false;
$cacheEntry['batches'][count( $cacheEntry['batches'] ) - 1][1] = false;
}
// Save partitions to memcached
$cache->set( $memcKey, $cacheEntry, self::CACHE_EXPIRY );
// Save backlink count to memcached
$memcKey = wfMemcKey( 'numbacklinks', md5( $this->title->getPrefixedDBkey() ), $table );
$cache->set( $memcKey, $cacheEntry['numRows'], self::CACHE_EXPIRY );
wfDebug( __METHOD__ . ": got from database\n" );
return $cacheEntry['batches'];
}
/**
* Partition a DB result with backlinks in it into batches
* @param ResultWrapper $res Database result
* @param int $batchSize
* @param bool $isComplete Whether $res includes all the backlinks
* @throws MWException
* @return array
*/
protected function partitionResult( $res, $batchSize, $isComplete = true ) {
$batches = [];
$numRows = $res->numRows();
$numBatches = ceil( $numRows / $batchSize );
for ( $i = 0; $i < $numBatches; $i++ ) {
if ( $i == 0 && $isComplete ) {
$start = false;
} else {
$rowNum = $i * $batchSize;
$res->seek( $rowNum );
$row = $res->fetchObject();
$start = (int)$row->page_id;
}
if ( $i == ( $numBatches - 1 ) && $isComplete ) {
$end = false;
} else {
$rowNum = min( $numRows - 1, ( $i + 1 ) * $batchSize - 1 );
$res->seek( $rowNum );
$row = $res->fetchObject();
$end = (int)$row->page_id;
}
# Sanity check order
if ( $start && $end && $start > $end ) {
throw new MWException( __METHOD__ . ': Internal error: query result out of order' );
}
$batches[] = [ $start, $end ];
}
return [ 'numRows' => $numRows, 'batches' => $batches ];
}
/**
* Get a Title iterator for cascade-protected template/file use backlinks
*
* @return TitleArray
* @since 1.25
*/
public function getCascadeProtectedLinks() {
$dbr = $this->getDB();
// @todo: use UNION without breaking tests that use temp tables
$resSets = [];
$resSets[] = $dbr->select(
[ 'templatelinks', 'page_restrictions', 'page' ],
[ 'page_namespace', 'page_title', 'page_id' ],
[
'tl_namespace' => $this->title->getNamespace(),
'tl_title' => $this->title->getDBkey(),
'tl_from = pr_page',
'pr_cascade' => 1,
'page_id = tl_from'
],
__METHOD__,
[ 'DISTINCT' ]
);
if ( $this->title->getNamespace() == NS_FILE ) {
$resSets[] = $dbr->select(
[ 'imagelinks', 'page_restrictions', 'page' ],
[ 'page_namespace', 'page_title', 'page_id' ],
[
'il_to' => $this->title->getDBkey(),
'il_from = pr_page',
'pr_cascade' => 1,
'page_id = il_from'
],
__METHOD__,
[ 'DISTINCT' ]
);
}
// Combine and de-duplicate the results
$mergedRes = [];
foreach ( $resSets as $res ) {
foreach ( $res as $row ) {
$mergedRes[$row->page_id] = $row;
}
}
return TitleArray::newFromResult(
new FakeResultWrapper( array_values( $mergedRes ) ) );
}
}