Manual:Job queue/fr

Avec MediaWiki 1.6, une file d'attente des travaux (ou job queue en anglais) a été introduite pour réaliser les longues opérations en tâche de fond. The job queue is designed to hold many short tasks using batch processing.

Set up
Whenever possible, you must set $wgJobRunRate to 0, and then use some sort of scheduler to run jobs completely in the background. For instance, if you were to use cron to run the jobs every day at midnight you would enter in your crontab file:

Job execution on page requests
By default, each time a page request runs, one job is taken from the job queue and executed. This behavior is controlled by the configuration variable. Setting this variable to, will run a job on each request. Setting this variable to a number between  and   will execute a job on average every   requests. Setting this variable to 0 will disable the execution of jobs during page requests completely, but you should run manually or periodically.

When enabled, jobs will be executed opening a socket and making an internal HTTP request to an unlisted special page: SpecialRunJobs.php. See the asynchronous section.

Performance issue
If the performance burden of this is too great, you can reduce by putting something like this in your LocalSettings.php:

Manual usage
There is also a way to empty the job queue manually, for example after changing a template that's present on many pages. Simply run the  maintenance script. For example:

Asynchronous
The configuration variable has been added to force the execution of jobs synchronously, in scenarios where making an internal HTTP request for job execution is not wanted.

When running jobs asynchronously, it will open an internal HTTP connection for handling the execution of jobs, and will return the contents of the page immediately to the client without waiting for the job to complete. Otherwise, the job will be executed in the same process and the client will have to wait until the job is completed. When the job does not run asynchronously, if a fatal error occurs during job execution, it will propagate to the client, aborting the load of the page.

Note that even if $wgRunJobsAsync is set to true, if PHP can't open a socket to make the internal HTTP request, it will fallback to the synchronous job execution. There are some configurations that can cause the asynchronous job execution to fail:


 * Run jobs async does not honor $wgServerName.
 * runJobs not following redirect.

Changes introduced in MediaWiki 1.22
In, the job queue execution on each page request was changed so, instead of executing the job inside the same PHP process that's rendering the page, a new PHP cli command is spawned to execute  in the background. It will only work if is set to an actual path or safe mode is off, otherwise, the old method will be used.

This new execution method could cause some problems:


 * If is set to an incompatible version of PHP (e.g.: an outdated version) jobs may fail to run (fixed in 1.23).
 * PHP  restrictions are in effect, and  is disallowed (, fixed in 1.23).
 * Performance: even if the job queue is empty, the new PHP process is started anyway (, fixed in 1.23).
 * Sometimes the spawning PHP process cause the server or only the CLI process to hang due to stdout and stderr descriptors not properly redirected (, fixed in 1.22)
 * It does not work for shared code (wiki farms), because it doesn't pass additional required parameters to runJobs.php to identify the wiki that's running the job (, fixed in 1.23)
 * Normal shell limits like, and  are enforced on the runJobs.php process that's being executed in the background.

There's no way to revert to the old on-request job queue handling, besides setting to , for example, which may cause other problems. It can be disabled completely by setting, but jobs will no longer run on page requests, and you must explicitly run runJobs.php to periodically run pending jobs.

Changes introduced in MediaWiki 1.23
In MediaWiki 1.23, the 1.22 execution method is abandoned, and jobs are triggered by MediaWiki making an HTTP connection to itself.

It was first designed as an API entry point but later changed to be an unlisted Special Page: SpecialRunJobs.php.

While it solves various bugs introduced in 1.22, it still requires loading a lot of PHP classes in memory on a new process to execute a job, and also makes a new HTTP request that the server must handle.

Mettre à jour la table des liens quand un modèle est modifié
MediaWiki 1.6 ajoute une tâche dans la file pour chaque article qui utilise un modèle modifié. Chaque tâche va lire l'article, substituer les modèles et modifier la table des liens en conséquence. Les modifications consistant à sauver une page sans en modifier le contenu (null edit) ne sont plus nécessaires, mais cela peut prendre un certain temps pour les modèles très utilisés. This can help to ease strain on a virtual person.

Invalidation du cache HTML
Une plus grande classe d'opérations consiste en l'invalidation du cache HTML pour un grand nombre de pages :


 * Modifier une image (toutes les miniatures seront mises à jour)
 * Suppression d'une page (tous les liens vers cette page passeront du bleu au rouge)
 * Création ou restauration d'une page (l'inverse du cas précédent)
 * Modifier un modèle (toutes les pages contenant ce modèle devront être mises à jour)

À l'exception des modifications de modèles, toutes ces opérations ne modifient pas la table des liens, mais elles invalident le cache HTML de toutes les pages liées. Invalider un cache est rapide, l'opération ne requiert la modification que d'un champ dans la base de données et l'envoi de requêtes de purge aux serveurs Squid si utilisés. Mais s'il y a plus de 1 000 pages à purger, cela peut prendre un certain temps. Par défaut, des tâches sont ajoutées uniquement s'il y a plus de 500 pages à invalider, une tâche par 500 pages.

Valeurs typiques
Pendant les périodes de faible affluence, la file peut être vide. Chez Wikimedia, la file n'est en pratique jamais vide. Pendant les heures creuses, elle peut avoir entre une centaine et quelques milliers de tâches. Mais pendant une journée chargée, elle peut atteindre plusieurs millions de tâches.

Voir l'état de la file d'attente
Up to MediaWiki 1.16, the job queue value was shown on Special:Statistics. Depuis la version 1.17, cela n'est plus visible dans les statistiques, il faut passer par l'API.

The number of jobs returned in the API result may be slightly inaccurate when using MySQL, which estimates the number of jobs in the database. This number can fluctuate based on the number of jobs that have recently been added or deleted. For other databases that do not support fast result-size estimation, the actual number of jobs is given.