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From "Maxim Grinev (JIRA)" <j...@apache.org>
Subject [jira] Commented: (CASSANDRA-1311) Support (asynchronous) triggers
Date Tue, 28 Dec 2010 10:40:51 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-1311?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12975462#action_12975462
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Maxim Grinev commented on CASSANDRA-1311:
-----------------------------------------

The implementation guarantees that triggers will be executed at least once even if the update
is only partially executed. The replicas that are updated will take care of that. It means
that if a write updates *some* replica and the write coordinator crashed before executing
triggers and acknowledging the client the triggers will be executed (as many times as the
number of replicas were updated). So missing an update is not a problem. Triggers are a good
solution for indexing. The only thing that is triggers are not good for is where the trigger
procedure is not idempontent. For example, when a trigger increments a counter, the counter
will be incremented with the same value more than once if the write coordinator failed. 

> 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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