Manual:Job queue/ja

MediaWiki 1.6 でジョブキューが導入され、長い処理を非同期的に実行できるようになりました. このジョブキューは、バッチ処理を用いて. 短い処理項目（ジョブ、job）を多数蓄えるように設計されています.

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 $wgJobRunRate 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 runJobs.php 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.

The configuration variable $wgRunJobsAsync 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.

履歴
Jobs were originally being run at the end of the page request, on the same process. This could cause problems if a PHP fatal error occurs during a job execution, aborting the load of the page.

MediaWiki 1.22 での変更点
In MediaWiki 1.22, 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 runJobs.php in the background. It will only work if $wgPhpCli 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 * If $wgPhpCli is set to an incompatible version of PHP (e.g.: an outdated version) jobs may fail to run (fixed in 1.23).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 $wgPhpCli 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 $wgMaxShellMemory, $wgMaxShellTime and $wgMaxShellFileSize are enforced on the runJobs.php process that's being executed in background.

There's no way to revert to the old on-request job queue handling, besides setting $wgPhpCli 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.

MediaWiki 1.23 での変更点
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 of the bugs introduced in 1.22, it still requires to load 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.

パフォーマンスの問題点
If the performance burden of this is too great, you can reduce $wgJobRunRate by putting something like this in your LocalSettings.php:

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/runJobs.php maintenance script. For example:

MediaWiki also allows you to set the $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:

Updating links tables when a template changes
When a template changes, MediaWiki adds a job to the job queue for each article transcluding that template. Each job is a command to read an article, expand any templates, and update the link table accordingly. So null edits are no longer necessary, although it may take a while for big operations to complete. This can help to ease strain on a virtual person.

HTMLキャッシュの無効化
大量のページに相当する既存のHTMLキャッシュを一気に無効にしてしまう操作は、〔テンプレートの改訂だけでなく〕より幅広い種類にわたります:


 * 画像の改訂（すべてのサムネイルを作り直し、大きさも再計算する必要があります）
 * ページの削除（すべてのリンク元でのリンクの色を、青から赤にする必要があります）
 * ページの作成、または復帰〔被削除物の回復. undelete. 復活とも〕（上記同様ですが、反対に赤から青にします）
 * テンプレートの改訂（テンプレートの参照読み込みされたページ〔のキャッシュ〕をすべて更新する必要があります）

テンプレートの改訂を除くこれらの操作の結果、リンクの表〔の内容〕が無効になることはありませんが、一方で、当該ページのリンク元の、あるいは当該画像の使用先の、すべてのページのHTMLキャッシュが無効になります. 1ページ分のキャッシュを無効にする処理はごく短く、必要なのはデータベースのフィールドを1件更新し、マルチキャストのパケットを1つ発してキャッシュを消すことだけです. しかしそれが1000件以上もある場合には、かなり時間がかかります. 初期設定では、500ページ分以上を無効化する必要のある場合のみ、500ページあたり1件の処理項目が〔ジョブキューに〕発生します (see $wgUpdateRowsPerJob).

特徴的な値
低負荷の期間に、ジョブキューはゼロであるかもしれません. Wikimedia でのジョブキューは、実際ほとんどゼロではありません. 混雑していない時間帯では数百から千であるかもしれません. 混雑している日の間では、それは数百万でもあり、１０％以上素早く上下します.

Special:Statistics
MediaWiki 1.16 まで、ジョブキューの長さは Special:Statistics に表示されました. ; 1.17 (75272) からそれは取り除かれて API:Meta で確認できます:

MySQL を使用している場合、MySQL がデータベース内のジョブ数を推定するため、API が返すジョブ数がわずかに正確ではないことがあります. この値は、最近追加または削除したジョブの数に応じて変動する場合があります. 他のデータベースは結果の高速推定に対応していないため、正確なジョブ数を返します.

開発者向け

 * Job queue for developers

関連項目

 * ジョブキューの設計変更
 * Manual:runJobs.php
 * Manual:showJobs.php
 * $wgJobRunRate
 * Manual:Job table