includes/jobqueue/utils/BacklinkJobUtils.php

   1 <?php
   2 /**
   3  * Job to update links for a given title.
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along
  16  * with this program; if not, write to the Free Software Foundation, Inc.,
  17  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  18  * http://www.gnu.org/copyleft/gpl.html
  19  *
  20  * @file
  21  * @ingroup JobQueue
  22  * @author Aaron Schulz
  23  */
  24
  25 /**
  26  * Class with Backlink related Job helper methods
  27  *
  28  * When an asset changes, a base job can be inserted to update all assets that depend on it.
  29  * The base job splits into per-title "leaf" jobs and a "remnant" job to handle the remaining
  30  * range of backlinks. This recurs until the remnant job's backlink range is small enough that
  31  * only leaf jobs are created from it.
  32  *
  33  * For example, if templates A and B are edited (at the same time) the queue will have:
  34  *     (A base, B base)
  35  * When these jobs run, the queue will have per-title and remnant partition jobs:
  36  *         (titleX,titleY,titleZ,...,A remnant,titleM,titleN,titleO,...,B remnant)
  37  *
  38  * This works best when the queue is FIFO, for several reasons:
  39  *   - a) Since the remnant jobs are enqueued after the leaf jobs, the slower leaf jobs have to
  40  *        get popped prior to the fast remnant jobs. This avoids flooding the queue with leaf jobs
  41  *        for every single backlink of widely used assets (which can be millions).
  42  *   - b) Other jobs going in the queue still get a chance to run after a widely used asset changes.
  43  *        This is due to the large remnant job pushing to the end of the queue with each division.
  44  *
  45  * The size of the queues used in this manner depend on the number of assets changes and the
  46  * number of workers. Also, with FIFO-per-partition queues, the queue size can be somewhat larger,
  47  * depending on the number of queue partitions.
  48  *
  49  * @ingroup JobQueue
  50  * @since 1.23
  51  */
  52 class BacklinkJobUtils {
  53         /**
  54          * Break down $job into approximately ($bSize/$cSize) leaf jobs and a single partition
  55          * job that covers the remaining backlink range (if needed). Jobs for the first $bSize
  56          * titles are collated ($cSize per job) into leaf jobs to do actual work. All the
  57          * resulting jobs are of the same class as $job. No partition job is returned if the
  58          * range covered by $job was less than $bSize, as the leaf jobs have full coverage.
  59          *
  60          * The leaf jobs have the 'pages' param set to a (<page ID>:(<namespace>,<DB key>),...)
  61          * map so that the run() function knows what pages to act on. The leaf jobs will keep
  62          * the same job title as the parent job (e.g. $job).
  63          *
  64          * The partition jobs have the 'range' parameter set to a map of the format
  65          * (start:<integer>, end:<integer>, batchSize:<integer>, subranges:((<start>,<end>),...)),
  66          * the 'table' parameter set to that of $job, and the 'recursive' parameter set to true.
  67          * This method can be called on the resulting job to repeat the process again.
  68          *
  69          * The job provided ($job) must have the 'recursive' parameter set to true and the 'table'
  70          * parameter must be set to a backlink table. The job title will be used as the title to
  71          * find backlinks for. Any 'range' parameter must follow the same format as mentioned above.
  72          * This should be managed by recursive calls to this method.
  73          *
  74          * The first jobs return are always the leaf jobs. This lets the caller use push() to
  75          * put them directly into the queue and works well if the queue is FIFO. In such a queue,
  76          * the leaf jobs have to get finished first before anything can resolve the next partition
  77          * job, which keeps the queue very small.
  78          *
  79          * $opts includes:
  80          *   - params : extra job parameters to include in each job
  81          *
  82          * @param Job $job
  83          * @param int $bSize BacklinkCache partition size; usually $wgUpdateRowsPerJob
  84          * @param int $cSize Max titles per leaf job; Usually 1 or a modest value
  85          * @param array $opts Optional parameter map
  86          * @return Job[] List of Job objects
  87          */
  88         public static function partitionBacklinkJob( Job $job, $bSize, $cSize, $opts = [] ) {
  89                 $class = get_class( $job );
  90                 $title = $job->getTitle();
  91                 $params = $job->getParams();
  92
  93                 if ( isset( $params['pages'] ) || empty( $params['recursive'] ) ) {
  94                         $ranges = []; // sanity; this is a leaf node
  95                         $realBSize = 0;
  96                         wfWarn( __METHOD__ . " called on {$job->getType()} leaf job (explosive recursion)." );
  97                 } elseif ( isset( $params['range'] ) ) {
  98                         // This is a range job to trigger the insertion of partitioned/title jobs...
  99                         $ranges = $params['range']['subranges'];
 100                         $realBSize = $params['range']['batchSize'];
 101                 } else {
 102                         // This is a base job to trigger the insertion of partitioned jobs...
 103                         $ranges = $title->getBacklinkCache()->partition( $params['table'], $bSize );
 104                         $realBSize = $bSize;
 105                 }
 106
 107                 $extraParams = isset( $opts['params'] ) ? $opts['params'] : [];
 108
 109                 $jobs = [];
 110                 // Combine the first range (of size $bSize) backlinks into leaf jobs
 111                 if ( isset( $ranges[0] ) ) {
 112                         list( $start, $end ) = $ranges[0];
 113                         $iter = $title->getBacklinkCache()->getLinks( $params['table'], $start, $end );
 114                         $titles = iterator_to_array( $iter );
 115                         /** @var Title[] $titleBatch */
 116                         foreach ( array_chunk( $titles, $cSize ) as $titleBatch ) {
 117                                 $pages = [];
 118                                 foreach ( $titleBatch as $tl ) {
 119                                         $pages[$tl->getArticleID()] = [ $tl->getNamespace(), $tl->getDBkey() ];
 120                                 }
 121                                 $jobs[] = new $class(
 122                                         $title, // maintain parent job title
 123                                         [ 'pages' => $pages ] + $extraParams
 124                                 );
 125                         }
 126                 }
 127                 // Take all of the remaining ranges and build a partition job from it
 128                 if ( isset( $ranges[1] ) ) {
 129                         $jobs[] = new $class(
 130                                 $title, // maintain parent job title
 131                                 [
 132                                         'recursive'     => true,
 133                                         'table'         => $params['table'],
 134                                         'range'         => [
 135                                                 'start'     => $ranges[1][0],
 136                                                 'end'       => $ranges[count( $ranges ) - 1][1],
 137                                                 'batchSize' => $realBSize,
 138                                                 'subranges' => array_slice( $ranges, 1 )
 139                                         ],
 140                                         // Track how many times the base job divided for debugging
 141                                         'division'      => isset( $params['division'] )
 142                                                 ? ( $params['division'] + 1 )
 143                                                 : 1
 144                                 ] + $extraParams
 145                         );
 146                 }
 147
 148                 return $jobs;
 149         }
 150 }