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Please hold: your call is in a queue. An introduction to queuing in Drupal.
 

Please hold: your call is in a queue. An introduction to queuing in Drupal.

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Please hold: your call is in a queue. An introduction to queuing in Drupal. ...

Please hold: your call is in a queue. An introduction to queuing in Drupal.

My talk from Drupalcamp London 1st-3rd March 2013. A version of this talk with minor modifications was also given at the Drupal Learning April 2013 meetup in London (http://www.meetup.com/Learning-Drupal-Meetup/events/111107222/).

It's not just the Brits that love queues, Drupal loves them too.

Maybe your website is making requests to another internal or third party system. Maybe a third party is sending messages to you. Either way, as you begin to grow your services are increasingly likely to run into problems completing these requests in a predictable amount of time and with guaranteed success.

Queueing is one solution to this, balancing load, ensuring jobs are processed successfully - but the uses don't end there.

This session will provide an overview of queueing patterns, discuss some scenarios where you may want to implement queues, and look at how Drupal implements queueing - as well as some of the gotchas in implementing queue processing at scale.

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    Please hold: your call is in a queue. An introduction to queuing in Drupal. Please hold: your call is in a queue. An introduction to queuing in Drupal. Presentation Transcript

    • PLEASE HOLD: YOUR CALL IS IN A QUEUE An introduction to queueing in Drupal by Tom PhetheanSunday, 3 March 13
    • QUEUING IN 30 MINUTES... •I hate waiting in line... • Drupal Queue API • Beyond Core • Queue jumpers and other gotchas • QuestionsSunday, 3 March 13
    • I HATE WAITING IN LINE...Sunday, 3 March 13
    • Sunday, 3 March 13
    • Sunday, 3 March 13
    • Sunday, 3 March 13
    • Sunday, 3 March 13
    • QUEUES WILL FORM WHEN PROCESSES WITH VARIABILITY ARE LOADED TO HIGH LEVELS OF UTILISATION WITHOUT CONSTRAINTSunday, 3 March 13
    • SOMETHING WILL QUEUE SOMEWHERESunday, 3 March 13
    • SOMETHING WILL QUEUE SOMEWHERE Whether you like it or notSunday, 3 March 13
    • DO YOU WANT TO BE IN CONTROL?Sunday, 3 March 13
    • <silly_question> DO YOU WANT TO BE IN CONTROL? </silly_question>Sunday, 3 March 13
    • DRUPAL TO THE RESCUE!Sunday, 3 March 13
    • CORE QUEUE API • Two kinds of queue: reliable and non-reliable • Provides interface to common queue functions • MemoryQueue implements QueueInterface • SystemQueue implements ReliableQueueInterface • In Drupal 7 (and 8), Batch API extends SystemQueueSunday, 3 March 13
    • WHERE CAN I FIND QUEUE API? • Drupal 7: • ./modules/system/system.queue.inc • Drupal 8: • ./core/lib/Drupal/Core/QueueSunday, 3 March 13
    • QUEUE API METHODS • createQueue() • numberOfItems() • createItem() • deleteItem() • claimItem() • deleteQueue() • releaseItem()Sunday, 3 March 13
    • Code time.Sunday, 3 March 13
    • /** * Create a queue. */ function queues_create_queue() { $queue = DrupalQueue::get(my_queue); $queue->createQueue(); }Sunday, 3 March 13
    • /** * Add an item to a queue. */ function queues_create_queueitem() { $queue = DrupalQueue::get(my_queue); $queue_data = array ( stuff => test, ); return $queue->createItem($queue_data); } /** * Check number of items on a queue. */ function queues_count_queueitems() { $queue = DrupalQueue::get(my_queue); return $queue->numberOfItems(); }Sunday, 3 March 13
    • /** * Process a queue item */ function queues_process_queueitem() { $queue = DrupalQueue::get(my_queue); $item = $queue->claimItem(30); if ($item && $item->data[stuff] == test) { // Success - we dont need this item anymore. $queue->deleteItem($item); } else { // Something unexpected happened, we still need this item. $queue->releaseItem($item); } }Sunday, 3 March 13
    • /** * Implements hook_cron_queue_info(). */ function queues_cron_queue_info() { $queues[my_queue] = array( worker callback => queues_process_queueitem, time => 60, // Time is NOT the lease item. // Time is the amount of time cron will spend processing this queue. ); return $queues; }Sunday, 3 March 13
    • /** * Implements hook_queue_info() from queue_ui module. */ function queues_queue_info() { return array( my_queue => array( title => t(My test queue), batch => array( operations => array(array(queues_batch_process, array())), finished => queues_batch_finished, title => t(Processing my test queue), ), cron => array( callback =>queues_process_queueitem, ), ), ); }Sunday, 3 March 13
    • That’s it!Sunday, 3 March 13
    • BEYOND CORE • Drupal Queue (backport to D6) - http://drupal.org/project/drupal_queue • Queue UI - http://drupal.org/project/queue_ui • Examples - http://drupal.org/project/examples • Queue backends: • Beanstalkd - http://drupal.org/project/beanstalkd • STOMP - http://drupal.org/project/stomp • Redis - http://drupal.org/project/redis_queueSunday, 3 March 13
    • CUSTOM BACKENDS • Default queue class: • $conf[queue_default_class] = SystemQueue; • $conf[‘queue_default_reliable_class’] = ‘SystemQueue’; • Override queue classes: • $conf[queue_class_{queue name}] = StompQueue;Sunday, 3 March 13
    • CUSTOM BACKENDS • Default queue class: • $conf[queue_default_class] = SystemQueue; • $conf[‘queue_default_reliable_class’] = ‘SystemQueue’; • Override queue classes: • $conf[queue_class_{queue name}] = RedisQueue;Sunday, 3 March 13
    • QUEUES AND DRUSH • drush queue-list • drush queue-run [queue name] • ...use with caution: queue-run will always delete your queue itemSunday, 3 March 13
    • WHEN TO QUEUE • Remote service call triggered by user interface • Complex business rules around data processing • Need guaranteed successSunday, 3 March 13
    • SOME EXAMPLES • Publishing user information to a remote CRM • Backend order fulfilment • Email sending (see notifications module)Sunday, 3 March 13
    • GOTCHASSunday, 3 March 13
    • MULTIPLE CONSUMERSSunday, 3 March 13
    • MULTIPLE CONSUMERS • Identify what it is you’re processing • Use Lock API to secure a lock on it: • lock_acquire(‘my_id’) • lock_release(‘my_id’) • Check the “thing” is in a state you expect it to be • Release or Delete from queue as appropriateSunday, 3 March 13
    • DEBUGGING YOUR QUEUESunday, 3 March 13
    • DEBUGGING YOUR QUEUE • watchdog() is your friend • Log EVERYTHING • Abstract it so you can toggle verbose logging • Use Graylog, LogStash etc to save your database from death by logsSunday, 3 March 13
    • THINGS CAN GO WRONG...Sunday, 3 March 13
    • THINGS CAN GO WRONG... • Monitor your queue depths with Munin or Nagios • Alert if they get too deep • Know what the alert means (and listen to it)!Sunday, 3 March 13
    • THINGS BREAK. BUT WHEN THEY DO, KNOW THAT EVERY ITEM IN YOUR QUEUE IS A REQUEST WHICH WOULD OTHERWISE HAVE BEEN LOST.Sunday, 3 March 13
    • IMPLEMENTING QUEUEING IN YOUR APPLICATION SMOOTHS THE PEAKS,Sunday, 3 March 13
    • IMPLEMENTING QUEUEING IN YOUR APPLICATION SMOOTHS THE PEAKS, MAKE THROUGHPUT PREDICTABLE,Sunday, 3 March 13
    • IMPLEMENTING QUEUEING IN YOUR APPLICATION SMOOTHS THE PEAKS, MAKE THROUGHPUT PREDICTABLE, REMOVES PROCESSING TIME FROM THE USER EXPERIENCESunday, 3 March 13
    • IMPLEMENTING QUEUEING IN YOUR APPLICATION SMOOTHS THE PEAKS, MAKE THROUGHPUT PREDICTABLE, REMOVES PROCESSING TIME FROM THE USER EXPERIENCE AND ENSURES THAT PROBLEMS ARE HANDLED GRACEFULLYSunday, 3 March 13
    • IN OTHER WORDS...Sunday, 3 March 13
    • Sunday, 3 March 13
    • QUESTIONS? Tweet: @tsphethean Drupal.org: tsphethean IRC: tsphetheanSunday, 3 March 13
    • IMAGE ATTRIBUTIONS • Image of supermarket queue - http://petoneponderings.blogspot.co.uk/2012_12_01_archive.html • Post Office queue - http://www.flickr.com/photos/welshkaren/5367517662/ • Apple Store queueing http://www.telegraph.co.uk/technology/apple/7854982/Apple-iPhone-4-more- than-a-quarter-of-users-think-video-calling-is-a-gimmick.html • Supermarket crush - http://www.dailymail.co.uk/news/article-2078597/Boxing-Day-sales-Record- numbers-shops-open-80-push-grab-shoppers.html • Drupal Superhero - http://www.origineight.net/blog-post/web-sites-you-manage • Lots of Shoppers - http://www.dailymail.co.uk/news/article-2253523/United-Nations-Bargain-Hunters- Britons-the-queue-China-Middle-East-lead-rush-designer-brands.html • Confused baby - http://thementalpausechronicles.blogspot.co.uk/2008/08/head-scratching.html • Mark Sonnabaum - http://www.whatwouldmarksonnabaumdo.comSunday, 3 March 13