Manual:Job queue/vi

From Linux Web Expert

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 $wgJobRunRate to 0.

You should run runJobs.php as the same user as the web server runs as, to ensure that permissions to the filesystem are correctly accounted for if jobs touch uploaded files.

Cron

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

0 * * * * /usr/bin/php /var/www/wiki/maintenance/runJobs.php --maxtime=3600 > /var/log/runJobs.log 2>&1

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 /usr/local/bin/mwjobrunner:

Create script

#!/bin/bash
# Put the MediaWiki installation path on the line below
MW_INSTALL_PATH="/home/www/www.mywikisite.example/mediawiki"
RUN_JOBS="$MW_INSTALL_PATH/maintenance/runJobs.php --maxtime=3600"
echo Starting job service...
# Wait a minute after the server starts up to give other processes time to get started
sleep 60
echo Started.
while true; do
	# Job types that need to be run ASAP no matter how many of them are in the queue
	# Those jobs should be very "cheap" to run
	php $RUN_JOBS --type="enotifNotify"
	# Everything else, limit the number of jobs on each batch
	# The --wait parameter will pause the execution here until new jobs are added,
	# to avoid running the loop without anything to do
	php $RUN_JOBS --wait --maxjobs=20
	# Wait some seconds to let the CPU do other things, like handling web requests, etc
	echo Waiting for 10 seconds...
	sleep 10
done

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 (chmod 755).

Create service

If using systemd, create a new service unit by creating the file /etc/systemd/system/mw-jobqueue.service. Change the User parameter to the user that runs PHP on your web server: 

[Unit]
Description=MediaWiki Job runner

[Service]
ExecStart=/usr/local/bin/mwjobrunner
Nice=10
ProtectSystem=full
User=php-fpm
OOMScoreAdjust=200
StandardOutput=journal

[Install]
WantedBy=multi-user.target

Enable it and start it with those commands: 

sudo systemctl enable mw-jobqueue
sudo systemctl start mw-jobqueue
sudo systemctl status mw-jobqueue

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 $wgJobRunRate configuration variable. Setting this variable to 1, will run a job on each request. Setting this variable to 0 will disable the execution of jobs during web requests completely, so that you can instead run runJobs.php manually or periodically from the command line.

Phiên bản MediaWiki:
<translate> ≥</translate> 1.23

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 $wgJobRunRate to a number between 1 and 0. This means a job will execute on average every 1 / $wgJobRunRate requests. 

$wgJobRunRate = 0.01;

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/runJobs.php maintenance script. For example: 

/path-to-my-wiki/maintenance$ php ./runJobs.php

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:

History

Asynchronous

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 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 EnqueueableDataUpdate 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 MediaWiki 1.22 , the job queue execution on each page request was changed (Gerrit change 59797) 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).

There's no way to revert to the old on-request job queue handling, besides setting $wgPhpCli to false, for example, which may cause other problems (<translate> task <tvar name=1>T63387</tvar></translate>). It can be disabled completely by setting $wgJobRunRate = 0;, 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 (Gerrit change 113038) but later changed to be the unlisted special page Special:RunJobs (Gerrit change 118336).

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 $wgRunJobsAsync would sometimes cause jobs not to get run if the wiki has custom $wgServerName configuration. This was fixed in MediaWiki 1.27.

<translate> task <tvar name=1>T107290</tvar></translate>

Changes in MediaWiki 1.28

Between MediaWiki 1.23 and MediaWiki 1.27, use of $wgRunJobsAsync 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.

<translate> task <tvar name=1>T68485</tvar></translate>

Changes in MediaWiki 1.29

In MediaWiki 1.27.0 to 1.27.3 and 1.28.0 to 1.28.2, when $wgJobRunRate 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 runJobs.php to clear the job queue. It has been reported as a bug (<translate> task <tvar name=1>T100085</tvar></translate>) 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 $wgUpdateRowsPerJob )

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 $wgUpdateRowsPerJob to a small number (20, for example) and also set $wgJobBackoffThrottling for htmlCacheUpdate to a low number (5, for example).

Audio and video transcoding

When using TimedMediaHandler 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 webVideoTranscode and webVideoTranscodePrioritized 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. [1]

Special:Statistics

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


api.php?action=query&meta=siteinfo&siprop=statistics [<translate> try in ApiSandbox</translate>]


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.

For developers

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