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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
* @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
*
* @internal documentation reviewed on 18 Mar 2011 by hashar
*/
class BacklinkCache {
/** @var ProcessCacheLRU */
protected static $cache;
/**
* Multi dimensions array representing batches. Keys are:
* > (string) links table name
* > 'numRows' : Number of rows for this link table
* > 'batches' : array( $start, $end )
*
* @see BacklinkCache::partitionResult()
*
* Cleared with BacklinkCache::clear()
*/
protected $partitionCache = array();
/**
* 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()
*/
protected $fullResultCache = array();
/**
* 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 $title ) {
if ( !self::$cache ) { // init cache
self::$cache = new ProcessCacheLRU( 1 );
}
$dbKey = $title->getPrefixedDBkey();
if ( !self::$cache->has( $dbKey, 'obj' ) ) {
self::$cache->set( $dbKey, 'obj', new self( $title ) );
}
return self::$cache->get( $dbKey, 'obj' );
}
/**
* 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 array( 'partitionCache', 'fullResultCache', 'title' );
}
/**
* Clear locally stored data and database object.
*/
public function clear() {
$this->partitionCache = array();
$this->fullResultCache = array();
unset( $this->db );
}
/**
* Set the Database object to use
*
* @param $db DatabaseBase
*/
public function setDB( $db ) {
$this->db = $db;
}
/**
* Get the slave connection to the database
* When non existing, will initialize the connection.
* @return DatabaseBase object
*/
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 $table String
* @param $startId Integer or false
* @param $endId Integer or false
* @return TitleArrayFromResult
*/
public function getLinks( $table, $startId = false, $endId = false ) {
wfProfileIn( __METHOD__ );
$fromField = $this->getPrefix( $table ) . '_from';
if ( $startId || $endId ) {
// Partial range, not cached
wfDebug( __METHOD__ . ": from DB (uncacheable range)\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 );
}
$res = $this->getDB()->select(
array( $table, 'page' ),
array( 'page_namespace', 'page_title', 'page_id' ),
$conds,
__METHOD__,
array(
'STRAIGHT_JOIN',
'ORDER BY' => $fromField
) );
$ta = TitleArray::newFromResult( $res );
wfProfileOut( __METHOD__ );
return $ta;
}
// @todo FIXME: Make this a function?
if ( !isset( $this->fullResultCache[$table] ) ) {
wfDebug( __METHOD__ . ": from DB\n" );
$res = $this->getDB()->select(
array( $table, 'page' ),
array( 'page_namespace', 'page_title', 'page_id' ),
$this->getConditions( $table ),
__METHOD__,
array(
'STRAIGHT_JOIN',
'ORDER BY' => $fromField,
) );
$this->fullResultCache[$table] = $res;
}
$ta = TitleArray::newFromResult( $this->fullResultCache[$table] );
wfProfileOut( __METHOD__ );
return $ta;
}
/**
* Get the field name prefix for a given table
* @param $table String
* @throws MWException
* @return null|string
*/
protected function getPrefix( $table ) {
static $prefixes = array(
'pagelinks' => 'pl',
'imagelinks' => 'il',
'categorylinks' => 'cl',
'templatelinks' => 'tl',
'redirect' => 'rd',
);
if ( isset( $prefixes[$table] ) ) {
return $prefixes[$table];
} else {
$prefix = null;
wfRunHooks( 'BacklinkCacheGetPrefix', array( $table, &$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 $table String
* @throws MWException
* @return array|null
*/
protected function getConditions( $table ) {
$prefix = $this->getPrefix( $table );
// @todo FIXME: imagelinks and categorylinks do not rely on getNamespace,
// they could be moved up for nicer case statements
switch ( $table ) {
case 'pagelinks':
case 'templatelinks':
$conds = array(
"{$prefix}_namespace" => $this->title->getNamespace(),
"{$prefix}_title" => $this->title->getDBkey(),
"page_id={$prefix}_from"
);
break;
case 'redirect':
$conds = array(
"{$prefix}_namespace" => $this->title->getNamespace(),
"{$prefix}_title" => $this->title->getDBkey(),
$this->getDb()->makeList( array(
"{$prefix}_interwiki" => '',
"{$prefix}_interwiki IS NULL",
), LIST_OR ),
"page_id={$prefix}_from"
);
break;
case 'imagelinks':
$conds = array(
'il_to' => $this->title->getDBkey(),
'page_id=il_from'
);
break;
case 'categorylinks':
$conds = array(
'cl_to' => $this->title->getDBkey(),
'page_id=cl_from',
);
break;
default:
$conds = null;
wfRunHooks( 'BacklinkCacheGetConditions', array( $table, $this->title, &$conds ) );
if( !$conds ) {
throw new MWException( "Invalid table \"$table\" in " . __CLASS__ );
}
}
return $conds;
}
/**
* Check if there are any backlinks
* @param $table String
* @return bool
*/
public function hasLinks( $table ) {
return ( $this->getNumLinks( $table, 1 ) > 0 );
}
/**
* Get the approximate number of backlinks
* @param $table String
* @param $max integer Only count up to this many backlinks
* @return integer
*/
public function getNumLinks( $table, $max = INF ) {
global $wgMemc;
// 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 = $wgMemc->get( $memcKey );
if ( $count ) {
return min( $max, $count );
}
// 4) fetch from the database ...
if ( is_infinite( $max ) ) { // full count
$count = $this->getLinks( $table )->count();
$wgMemc->set( $memcKey, $count, self::CACHE_EXPIRY );
} else { // with limit
$count = $this->getDB()->select(
array( $table, 'page' ),
'1',
$this->getConditions( $table ),
__METHOD__,
array( 'LIMIT' => $max )
)->numRows();
}
return $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 $batchSize Integer
* @return Array
*/
public function partition( $table, $batchSize ) {
global $wgMemc;
// 1) try partition cache ...
if ( isset( $this->partitionCache[$table][$batchSize] ) ) {
wfDebug( __METHOD__ . ": got from partition cache\n" );
return $this->partitionCache[$table][$batchSize]['batches'];
}
$this->partitionCache[$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 = $wgMemc->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 :(
$this->getLinks( $table );
$cacheEntry = $this->partitionResult( $this->fullResultCache[$table], $batchSize );
// Save partitions to memcached
$wgMemc->set( $memcKey, $cacheEntry, self::CACHE_EXPIRY );
// Save backlink count to memcached
$memcKey = wfMemcKey( 'numbacklinks', md5( $this->title->getPrefixedDBkey() ), $table );
$wgMemc->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 $res ResultWrapper database result
* @param $batchSize integer
* @throws MWException
* @return array @see
*/
protected function partitionResult( $res, $batchSize ) {
$batches = array();
$numRows = $res->numRows();
$numBatches = ceil( $numRows / $batchSize );
for ( $i = 0; $i < $numBatches; $i++ ) {
if ( $i == 0 ) {
$start = false;
} else {
$rowNum = intval( $numRows * $i / $numBatches );
$res->seek( $rowNum );
$row = $res->fetchObject();
$start = $row->page_id;
}
if ( $i == $numBatches - 1 ) {
$end = false;
} else {
$rowNum = intval( $numRows * ( $i + 1 ) / $numBatches );
$res->seek( $rowNum );
$row = $res->fetchObject();
$end = $row->page_id - 1;
}
# Sanity check order
if ( $start && $end && $start > $end ) {
throw new MWException( __METHOD__ . ': Internal error: query result out of order' );
}
$batches[] = array( $start, $end );
}
return array( 'numRows' => $numRows, 'batches' => $batches );
}
}