Basics of Sitecore Event Queue

Sitecore 6.3 got nice feature called Event Queue. This is nice article on it : http://www.sitecore.net/Community/Technical-Blogs/Getting-to-Know-Sitecore/Posts/2010/07/Introducing-the-Sitecore-Event-Queue.aspx

Updated : 10th May 2011

Was reading Forum and Adam Weber wrote nice stuff on EventQueue, which will really help you to clear your Event Queue Basics:

Here are some quick, easy steps to enable event queues and subsequently clear your CD html caches on publish:

1) Either “enable” the /App_Config/Include/ScalabilitySettings.config file by removing the .example extension and deploying it to ALL of your Sitecore instances (both CM and CD). Or, in your web.config file (or another include file) change the /sitecore/settings/EnableEventQueues setting to “true”. Then deploy your adjusted web.config to all of your Sitecore instances.

2) In your web.config file, check the /sitecore/events node and verify that you see a node similar to this:
<event name=”publish:end:remote”>
<handler type=”Sitecore.Publishing.HtmlCacheClearer, Sitecore.Kernel” method=”ClearCache”>
<sites hint=”list”>
<site>website</site>
</sites>
</handler>
</event>
This handler(s) listed for this event are fired on your remote Sitecore instances (typically CD environments) after a publish operation completes. Ensure that the HtmlCacheClearer handler is in place and that the parameter contains a element with the name of the remote site you’re attempting to clear the cache for. Out of the box, the default “public” site for Sitecore is named “website”. If you’ve changed that name at all then you need to adjust the HtmlCacheClearer parameter accordingly. You can see all of the sites defined in your web.config file under the /sitecore/sites node.

Lastly, here is a brief overview of how the event queue works, assuming the ‘EnableEventQueues’ setting is true for your relevant Sitecore instances:
1) Your CM instance triggers an event, for instance “publish:end:remote”
2) This event is added to the EventQueue table in the database that is targeted by the event. For instance, the “publish:end:remote” event will be queued up in the publishing target database, typically the ‘web’ database (unless you’ve specified custom publishing targets/databases).
3) Every 2 seconds, your CD instances poll the EventQueue table in the database from which they are retrieving content. If they find an event queued up in the EventQueue table, they attempt to handle the event according to the handlers defined in the /sitecore/events section in their respective web.config files. For instance, by default the “publish:end:remote” event is configured to execute the HtmlCacheClearer handler for the “website” site. Handlers can be added or removed as needed. (Note: the interval at which your CD instances poll the EventQueue table is configurable in the web.config file under the /sitecore/eventQueue/processingInterval node)

Sitecore Scaling Guide

Happy Event Queuing! 🙂