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https://issues.apache.org/jira/browse/CASSANDRA-1311?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12975311#action_12975311
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David Erickson commented on CASSANDRA-1311:
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I haven't dug into this implementation of triggers, but the use case we had in 
mind is using the database as a shared communication bus amongst distributed 
nodes.  If node 1 makes a change to its Cassandra instance, once the data 
propagates to the other Cassandra instances the triggers can alert other nodes 
that a change has been made and they need to do some processing.  This is much 
better than polling for changes.  Alternatively the nodes would have to have 
their own protocol to alert each other outside of the database layer that 
changes have been made.

> Support (asynchronous) triggers
> -------------------------------
>
>                 Key: CASSANDRA-1311
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-1311
>             Project: Cassandra
>          Issue Type: New Feature
>          Components: Contrib
>            Reporter: Maxim Grinev
>             Fix For: 0.8
>
>         Attachments: HOWTO-PatchAndRunTriggerExample-update1.txt, 
> HOWTO-PatchAndRunTriggerExample.txt, ImplementationDetails-update1.pdf, 
> ImplementationDetails.pdf, trunk-967053.txt, trunk-984391-update1.txt, 
> trunk-984391-update2.txt
>
>
> Asynchronous triggers is a basic mechanism to implement various use cases of 
> asynchronous execution of application code at database side. For example to 
> support indexes and materialized views, online analytics, push-based data 
> propagation.
> Please find the motivation, triggers description and list of applications:
> http://maxgrinev.com/2010/07/23/extending-cassandra-with-asynchronous-triggers/
> An example of using triggers for indexing:
> http://maxgrinev.com/2010/07/23/managing-indexes-in-cassandra-using-async-triggers/
> Implementation details are attached.

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