<?php
+/**
+ * File for BacklinkCache class
+ * @file
+ */
/**
- * Class for fetching backlink lists, approximate backlink counts and partitions.
- * Instances of this class should typically be fetched with $title->getBacklinkCache().
+ * 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
*
- * 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.
+ * @internal documentation reviewed on 18 Mar 2011 by hashar
+ *
+ * @author Tim Starling
+ * @copyright © 2009, Tim Starling, Domas Mituzas
+ * @copyright © 2010, Max Sem
+ * @copyright © 2011, Antoine Musso
*/
class BacklinkCache {
- var $partitionCache = array();
- var $fullResultCache = array();
- var $title;
- var $db;
+
+ /**
+ * 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.
*/
function __construct( $title ) {
$this->title = $title;
}
/**
- * Clear locally stored data
+ * 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.
*/
- function clear() {
+ 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 string $table
- * @return TitleArray
+ * @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" );
+ 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.
- $fromField = $this->getPrefix( $table ) . '_from';
if ( $startId ) {
$conds[] = "$fromField >= " . intval( $startId );
}
+
if ( $endId ) {
$conds[] = "$fromField <= " . intval( $endId );
}
- $res = $this->getDB()->select(
- array( 'page', $table ),
+
+ $res = $this->getDB()->select(
+ array( $table, 'page' ),
array( 'page_namespace', 'page_title', 'page_id' ),
$conds,
- __METHOD__ );
+ __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( 'page', $table ),
+ wfDebug( __METHOD__ . ": from DB\n" );
+ $res = $this->getDB()->select(
+ array( $table, 'page' ),
array( 'page_namespace', 'page_title', 'page_id' ),
$this->getConditions( $table ),
- __METHOD__ );
+ __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
+ * @return null|string
*/
protected function getPrefix( $table ) {
static $prefixes = array(
- 'pagelinks' => 'pl',
- 'imagelinks' => 'il',
+ 'pagelinks' => 'pl',
+ 'imagelinks' => 'il',
'categorylinks' => 'cl',
'templatelinks' => 'tl',
- 'redirect' => 'rd',
+ 'redirect' => 'rd',
);
+
if ( isset( $prefixes[$table] ) ) {
return $prefixes[$table];
} else {
- throw new MWException( "Invalid table \"$table\" in " . __CLASS__ );
+ $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
+ * Get the SQL condition array for selecting backlinks, with a join
+ * on the page table.
+ * @param $table String
+ * @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" => $this->title->getDBkey(),
+ "{$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(
+ $conds = array(
'il_to' => $this->title->getDBkey(),
'page_id=il_from'
);
break;
case 'categorylinks':
- $conds = array(
+ $conds = array(
'cl_to' => $this->title->getDBkey(),
'page_id=cl_from',
);
break;
default:
- throw new MWException( "Invalid table \"$table\" in " . __CLASS__ );
+ $conds = null;
+ wfRunHooks( 'BacklinkCacheGetConditions', array( $table, $this->title, &$conds ) );
+ if( !$conds )
+ throw new MWException( "Invalid table \"$table\" in " . __CLASS__ );
}
+
return $conds;
}
/**
* Get the approximate number of backlinks
+ * @param $table String
+ * @return integer
*/
public function getNumLinks( $table ) {
if ( isset( $this->fullResultCache[$table] ) ) {
return $this->fullResultCache[$table]->numRows();
}
+
if ( isset( $this->partitionCache[$table] ) ) {
$entry = reset( $this->partitionCache[$table] );
return $entry['numRows'];
}
+
$titleArray = $this->getLinks( $table );
+
return $titleArray->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.
+ * 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 integer $batchSize
- * @return array
+ * @param $table String: the links table name
+ * @param $batchSize Integer
+ * @return Array
*/
public function partition( $table, $batchSize ) {
- // Try cache
+
+ // 1) try partition cache ...
+
if ( isset( $this->partitionCache[$table][$batchSize] ) ) {
- wfDebug( __METHOD__.": got from partition cache\n" );
+ wfDebug( __METHOD__ . ": got from partition cache\n" );
return $this->partitionCache[$table][$batchSize]['batches'];
}
+
$this->partitionCache[$table][$batchSize] = false;
$cacheEntry =& $this->partitionCache[$table][$batchSize];
- // Try full result cache
+ // 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" );
+ wfDebug( __METHOD__ . ": got from full result cache\n" );
+
return $cacheEntry['batches'];
}
- // Try memcached
+
+ // 3) ... fallback to memcached ...
+
global $wgMemc;
- $memcKey = wfMemcKey( 'backlinks', md5( $this->title->getPrefixedDBkey() ),
- $table, $batchSize );
+
+ $memcKey = wfMemcKey(
+ 'backlinks',
+ md5( $this->title->getPrefixedDBkey() ),
+ $table,
+ $batchSize
+ );
+
$memcValue = $wgMemc->get( $memcKey );
+
if ( is_array( $memcValue ) ) {
$cacheEntry = $memcValue;
- wfDebug( __METHOD__.": got from memcached $memcKey\n" );
+ wfDebug( __METHOD__ . ": got from memcached $memcKey\n" );
+
return $cacheEntry['batches'];
}
- // Fetch from database
+
+
+ // 4) ... finally fetch from the slow database :(
+
$this->getLinks( $table );
$cacheEntry = $this->partitionResult( $this->fullResultCache[$table], $batchSize );
// Save to memcached
$wgMemc->set( $memcKey, $cacheEntry, self::CACHE_EXPIRY );
- wfDebug( __METHOD__.": got from database\n" );
+
+ 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
+ * @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;
$row = $res->fetchObject();
$start = $row->page_id;
}
+
if ( $i == $numBatches - 1 ) {
$end = false;
} else {
$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 );
}
}
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