Manual:Job queue/vi

Trong MediaWiki 1.6, một hàng đợi việc đã được đưa vào sử dụng để thực hiện một cách không đồng bộ những tác vụ dài hơi. Hàng đợi việc được thiết kế để chứa nhiều tác vụ ngắn bằng cách dùng xử lý theo gói.

Set up
It is recommended that you instead schedule the running of jobs completely in the background, via the command line. By default, jobs are run at the end of a web request. Disable this default behaviour by setting to.

Cron
You could use cron to run the jobs every hour. Add the following to your crontab file:

Using Cron makes it easy to get started, but can make email notifications and cascading template feel slow (to wait up to an hour). Consider using one of the below approaches to set up a continuous job runner instead.

Continuous service
If you have shell access and the possibility to create init scripts, you can create a simple service to run jobs as they become available, and also throttle them to prevent the job runner to monopolise the CPU resources of the server:

Create a bash script, for example at :

Create script
Depending on how fast the server is and the load it handles, you can adapt the number of jobs to run on each cycle and the number of seconds to wait on each cycle.

Make the script executable.

Create service
If using systemd, create a new service unit by creating the file. Change the  parameter to the user that runs PHP on your web server:

Enable it and start it with those commands:

Job execution on page requests
By default, at the end of each web request, one job is taken from the job queue and executed. This behaviour is controlled by the configuration variable. Setting this variable to, will run a job on each request. Setting this variable to  will disable the execution of jobs during web requests completely, so that you can instead run  manually or periodically from the command line.

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

Performance issue
If the performance burden of running jobs on every web request is too great but you are unable to run jobs from the command line, you can reduce to a number between   and. This means a job will execute on average every  requests.

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:

Abandoned jobs
A job can fail for some reasons. To understand why, you have to inspect the related log file.

In any case, if a job fails 3 times (so if the system has done that number of attempts), the job is then considered "abandoned" and it's not executed again.

Relevant source code:

https://doc.wikimedia.org/mediawiki-core/master/php/JobQueue_8php_source.html#l00085

An abandoned job is:


 * not executed anymore from
 * not counted from
 * not automatically removed from the database
 * but are included in the count of Special:Statistics

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 fall back to the synchronous job execution. However, there are a variety of situations where this internal request may fail, and jobs won't be run, without falling back to the synchronous job execution. Starting with MediaWiki 1.28.1 and 1.27.2, $wgRunJobsAsync now defaults to false.

Deferred updates
The deferred updates mechanism allows the execution of code to be scheduled for the end of the request, after all content has been sent to the browser. This is similar to queuing a job, except that it runs immediately instead of upto several minutes/hours in the future.

DeferredUpdates was introduced in MediaWiki 1.23 and received major changes during MediaWiki 1.27 and 1.28. The goal of this mechanism is speed up the web responses by doing less work, as well as to prioritise some work that would previously be a job to run as soon as possible after the end of the response.

A deferrable update can implement  in order to be queueable as a Job as well. This is used by RefreshSecondaryDataUpdate in core, for example, which means if the update fails for any reason, MediaWiki will fallback to queuing as a job and try again later as to fulfil the contract in question.

Changes 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 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 the unlisted special page Special:RunJobs.

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.

Changes in MediaWiki 1.27
In MediaWiki 1.25 and MediaWiki 1.26, use of would sometimes cause jobs not to get run if the wiki has custom   configuration. This was fixed in MediaWiki 1.27.

Changes in MediaWiki 1.28
Between MediaWiki 1.23 and MediaWiki 1.27, use of would cause jobs not to get run on if MediaWiki requests are for a server name or protocol that does not match the currently configured server name one (e.g. when supporting both HTTP and HTTPS, or when MediaWiki is behind a reverse proxy that redirects to HTTPS). This was fixed in MediaWiki 1.28.

Changes in MediaWiki 1.29
In MediaWiki 1.27.0 to 1.27.3 and 1.28.0 to 1.28.2, when is set to a value greater than 0, an error like the one below may appear in error logs, or on the page:

PHP Notice: JobQueueGroup::__destruct: 1 buffered job(s) never inserted

As a result of this error, certain updates may fail in some cases, like category members not being updated on category pages, or recent changes displaying edits of deleted pages - even if you manually run to clear the job queue. It has been reported as a bug and was solved in 1.27.4 and 1.28.3.

Job examples


Cập nhật bảng liên kết khi một tiêu bản bị thay đổi
MediaWiki 1.6 thêm một công việc vào hàng đợi việc cho mỗi bài viết sử dụng một tiêu bản. Mỗi công việc là một câu lệnh để đọc bài viết, bung các tiêu bản trong đó, và cập nhật bảng liên kết tương ứng. Trước đây, các bài viết trên máy chủ lưu trữ sẽ vẫn lỗi thời cho đến khi bộ đệm phân tích cú pháp của chúng hết hạn hoặc cho đến khi người dùng chỉnh sửa bài viết.



Mất hiệu lực bộ đệm HTML
Một loại tác vụ rộng hơn có thể dẫn đến mất hiệu lực bộ đệm (cache) HTML của một số lượng lớn các trang:


 * Thay đổi một hình ảnh (tất cả các hình thu nhỏ phải được kết xuất lại, và kích thước của chúng phải được tính toán lại)
 * Xóa một trang (tất cả các liên kết đến nó từ các trang khác phải thay đổi từ màu xanh sang màu đỏ)
 * Tạo hoặc phục hồi một trang (như ở trên, nhưng từ đỏ sang xanh)
 * Thay đổi một tiêu bản (tất cả các trang có nhúng tiêu bản phải cập nhật lại)

Ngoại trừ thay đổi tiêu bản, những tác vụ này không làm mất hiệu lực các bảng liên kết, mà chúng chỉ làm mất hiệu lực bộ đệm HTML của tất cả các trang liên kết đến trang đó, hoặc sử dụng hình ảnh đó. Việc làm mất hiệu lực bộ đệm của một trang là một tác vụ ngắn; chỉ cần cập nhật một trường cơ sở dữ liệu rồi gửi một gói multicast để xóa bộ đệm. Nhưng nếu có hơn 1000 việc phải làm, sẽ mất thời gian. Theo mặc định, những công việc được thêm vào khi cần làm mất hiệu lực hơn 500 trang, mỗi công việc tương ứng 300 tác vụ. (xem trang )

Note, however, that even if purging the cache of a page is a short operation, reparsing a complex page that is not in the cache may be expensive, especially if a highly used template is edited and causes lots of pages to be purged in a short period of time and your wiki has lots of concurrent visitors loading a wide spread of pages. This can be mitigated by reducing the number of pages purged in a short period of time, by reducing to a small number (20, for example) and also set  for   to a low number (5, for example).

Audio and video transcoding
When using to process local uploads of audio and video files, the job queue is used to run the potentially very slow creation of derivative transcodes at various resolutions/formats.

These are not suitable for running on web requests -- you will need a background runner.

It's recommended to set up separate runners for the  and   job types if possible. These two queues process different subsets of files -- the first for high resolution HD videos, and the second for lower-resolution videos and audio files which process more quickly.



Các giá trị thực tế
Khi có lượng tải thấp, hàng đợi việc có thể sẽ là zero. Tại Wikimedia, trên thực tế, hàng đợi việc hầu như không bao giờ zero cả. Vào những giờ cao điểm, nó có thể lên tới vài trăm đến cả ngàn. Trong một ngày bận rộn, có thể là cả triệu, nhưng có thể nhanh chóng dao động trong khoảng 10% hoặc hơn.

Special:Statistics
Up to MediaWiki 1.16, the job queue value was shown on Special:Statistics. However, since 1.17 (75272) it's been removed, and can be seen now with :

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.

Code stewardship
