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<?php
/**
* Class for fetching backlink lists, approximate backlink counts and partitions.
* Instances of this class should typically be fetched with $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.
*/
class BacklinkCache {
var $partitionCache = array();
var $fullResultCache = array();
var $title;
var $db;
const CACHE_EXPIRY = 3600;
/**
* Create a new BacklinkCache
*/
function __construct( $title ) {
$this->title = $title;
}
/**
* Clear locally stored data
*/
function clear() {
$this->partitionCache = array();
$this->fullResultCache = array();
unset( $this->db );
}
/**
* Set the Database object to use
*/
public function setDB( $db ) {
$this->db = $db;
}
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
*/
public function getLinks( $table, $startId = false, $endId = false ) {
wfProfileIn( __METHOD__ );
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.
$fromField = $this->getPrefix( $table ) . '_from';
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') );
$ta = TitleArray::newFromResult( $res );
wfProfileOut( __METHOD__ );
return $ta;
}
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') );
$this->fullResultCache[$table] = $res;
}
$ta = TitleArray::newFromResult( $this->fullResultCache[$table] );
wfProfileOut( __METHOD__ );
return $ta;
}
/**
* Get the field name prefix for a given table
*/
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 {
throw new MWException( "Invalid table \"$table\" in " . __CLASS__ );
}
}
/**
* Get the SQL condition array for selecting backlinks, with a join on the page table
*/
protected function getConditions( $table ) {
$prefix = $this->getPrefix( $table );
switch ( $table ) {
case 'pagelinks':
case 'templatelinks':
case 'redirect':
$conds = array(
"{$prefix}_namespace" => $this->title->getNamespace(),
"{$prefix}_title" => $this->title->getDBkey(),
"page_id={$prefix}_from"
);
break;
case 'imagelinks':
$conds = array(
'il_to' => $this->title->getDBkey(),
'page_id=il_from'
);
break;
case 'categorylinks':
$conds = array(
'cl_to' => $this->title->getDBkey(),
'page_id=cl_from',
);
break;
default:
throw new MWException( "Invalid table \"$table\" in " . __CLASS__ );
}
return $conds;
}
/**
* Get the approximate number of backlinks
*/
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.
*
* @param string $table The links table name
* @param integer $batchSize
* @return array
*/
public function partition( $table, $batchSize ) {
// Try 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];
// 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'];
}
// Try memcached
global $wgMemc;
$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" );
return $cacheEntry['batches'];
}
// Fetch from 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" );
return $cacheEntry['batches'];
}
/**
* Partition a DB result with backlinks in it into batches
*/
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;
}
$batches[] = array( $start, $end );
}
return array( 'numRows' => $numRows, 'batches' => $batches );
}
}
|
