I've got an application that uses Beanstalkd to queue up messages, and some PHP worker scripts that grab messages from the queue and process them. Messages get added by the web application, but can also be added by cron - and when I add a bunch of messages via cron, I don't want to swamp what the web application is doing! Those cron-added jobs are mostly pretty low priority, generating reports, sending weekly update emails, that kind of thing. Beanstalkd has a concept of priority, so I can create lower priority jobs by using code like this:
define("LOW_PRIORITY", 2048); // default is 1024
$queue = new Pheanstalk_Pheanstalk($config['beanstalkd']['host'] . ":" . $config['beanstalkd']['port']);
$queue->useTube("scorem")->put(json_encode(array("action" => "my_important_task")), LOW_PRIORITY);
This will add the job to the queue, but anything with a higher priority value (where 1 is the highest priority!) will take precendence. This way I can add as many non-urgent jobs as I want to to the queue without impacting my website performance. My setup has multiple workers and also I tend to write a script that puts loads of tiny jobs on the queue rather than putting one monster task on there. I find this approach a bit more fault-tolerant and also means that incoming tasks can get a chance to get serviced rather than waiting for some crazy huge thing to finish.
I had real issues finding information about the priority settings for beanstalkd and PHP, so hopefully if anyone is looking for it, they will find this post :)