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From "rektide de la fey (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-1311) Triggers
Date Fri, 18 Jan 2013 18:16:16 GMT


rektide de la fey commented on CASSANDRA-1311:

Hi, this ticket seems well underway and I apologize if chiming in like this is inappropriate.

Rather than trying to define work to do as a part of the trigger (as conventional databases
often do), my chief interest would be simply noting or recording certain conditions as they
occur, in a way that external systems can themselves trigger responsive actions to be taken
(hopefully in a low-latency fashion).

Decoupling the detection from the follow up processing will make for a far more flexible system,
and allows for general reactivity in the Cassandra world, rather than trying to define a good
enough suite of actions can be taken in the DB layer proper. Providing hooks which external
applications can use to do asynchronous trigger actions will also be critical for responsive/reactive
system design, freeing systems from having to create their own event logs, and allowing them
to simply monitor what's going on inside the database.

The topic of finding out what execution engine to make, what to do when one is triggered,
is a huge huge huge undertaking which will certainly not be done right. Please please please,
decouple the problem into it's component pieces as I am requesting: a reactive trigger, which
can detect changes and raise notices, and secondarily, an execution engine inside Cassandra
which can subscribe to event sources and perform operations when changes are detected. It's
vital that external applications have a means to detect & react to changes, and doing
triggers internally only takes on too small & narcissistic a problem, and carries with
it the weight of having to build an execution engine to do work on the trigger.
> Triggers
> --------
>                 Key: CASSANDRA-1311
>                 URL:
>             Project: Cassandra
>          Issue Type: New Feature
>            Reporter: Maxim Grinev
>            Assignee: Vijay
>             Fix For: 2.0
>         Attachments: HOWTO-PatchAndRunTriggerExample.txt, HOWTO-PatchAndRunTriggerExample-update1.txt,
ImplementationDetails.pdf, ImplementationDetails-update1.pdf, trunk-967053.txt, trunk-984391-update1.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:
> An example of using triggers for indexing:
> Implementation details are attached.

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