Using Queue Daemons

Queues and Daemons

Some activities that GNU social needs to do, like broadcast OStatus, SMS, XMPP messages and TwitterBridge operations, can be ‘queued’ and done by off-line bots instead.

Two mechanisms are available to achieve offline operations:

  • New embedded OpportunisticQM plugin, which is enabled by default
  • Legacy queuedaemon script, which can be enabled via config file.

OpportunisticQM plugin

This plugin is enabled by default. It tries its best to do background jobs during regular HTTP requests, like API or HTML pages calls.

Since queueing system is enabled by default, notices to be broadcasted will be stored, by default, into DB (table queue_item).

Whenever it has time, OpportunisticQM will try to handle some of them.

This is a good solution whether you:

  • have no access to command line (shared hosting)
  • do not want to deal with long-running PHP processes
  • run a low traffic GNU social instance

In other case, you really should consider enabling the queuedaemon for performance reasons. Background daemons are necessary anyway if you wish to use the Instant Messaging features such as communicating via XMPP.

queuedaemon

If you want to use legacy queuedaemon, you must be able to run long-running offline processes, either on your main Web server or on another server you control. (Your other server will still need all the above prerequisites, with the exception of Apache.) Installing on a separate server is probably a good idea for high-volume sites.

  1. You’ll need the “CLI” (command-line interface) version of PHP installed on whatever server you use.

Modern PHP versions in some operating systems have disabled functions related to forking, which is required for daemons to operate. To make this work, make sure that your php-cli config (/etc/php5/cli/php.ini) does NOT have these functions listed under ‘disable_functions’:

  • pcntl_fork, pcntl_wait, pcntl_wifexited, pcntl_wexitstatus, pcntl_wifsignaled, pcntl_wtermsig

Other recommended settings for optimal performance are:

  • mysqli.allow_persistent = On
  • mysqli.reconnect = On

  1. If you’re using a separate server for queues, install GNU social somewhere on the server. You don’t need to worry about the .htaccess file, but make sure that your config.php file is close to, or identical to, your Web server’s version.

  2. In your config.php files (on the server where you run the queue daemon), set the following variable:

    $config['queue']['daemon'] = true;

  3. On the queues server, run the command scripts/startdaemons.sh.

This will run the queue handlers:

queuedaemon.php
polls for queued items for inbox processing and pushing out to OStatus, SMS, XMPP, etc.
imdaemon.php
if an IM plugin is enabled (like XMPP)
(plugins)
other daemons, like TwitterBridge ones, that you may have enabled

These daemons will automatically restart in most cases of failure including memory leaks (if a memory_limit is set), but may still die or behave oddly if they lose connections to the XMPP or queue servers.

It may be a good idea to use a daemon-monitoring service, like ‘monit’, to check their status and keep them running.

All the daemons write their process IDs (pids) to /var/run/ by default. This can be useful for starting, stopping, and monitoring the daemons. If you are running multiple sites on the same machine, it will be necessary to avoid collisions of these PID files by setting a site-specific directory in config.php:

$config['daemon']['piddir'] = __DIR__ . '/../run/';

It is also possible to use a STOMP server instead of our kind of hacky home-grown DB-based queue solution. This is strongly recommended for best response time, especially when using XMPP.