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From "Sylvain Lebresne (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-4684) Binary protocol: inform clients of schema changes
Date Tue, 02 Oct 2012 17:05:07 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-4684?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13467866#comment-13467866
] 

Sylvain Lebresne commented on CASSANDRA-4684:
---------------------------------------------

The use case is for client that want to maintain a view of the schema up to date. After all,
with CQL3 we're going into a more typed world, so it make sense that high level client would
need to know about those types. For instance, you cannot form a query properly unless you
know the schema. And in 1.2, creating tables dynamically will be a fully supported use case,
so in that case you will likely need to access the current schema programatically. But even
without that, I'm pretty sure that any advanced tooling like say a good eclipse plugin will
need to keep an up to date view of the schema.

Without this patch, said client will have to either query the schema each and every time they
need it, or implement some form of ad-hoc polling. But events are here exactly to avoid having
to do polling (and clients will already have support for events, so it will much easier for
them to have this).
                
> Binary protocol: inform clients of schema changes
> -------------------------------------------------
>
>                 Key: CASSANDRA-4684
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-4684
>             Project: Cassandra
>          Issue Type: Improvement
>    Affects Versions: 1.2.0 beta 1
>            Reporter: Sylvain Lebresne
>            Assignee: Sylvain Lebresne
>            Priority: Minor
>             Fix For: 1.2.0 beta 2
>
>         Attachments: 0001-Return-schema-change-infos.txt, 0002-Add-migration-events.txt
>
>
> It would be nice to inform clients when a schema change occurs as this would allow said
client to maintain the current state of the schema, which might be useful/desirable. To allow
that, we can:
> # return that a query has changed the schema (instead of simply a 'void' return), in
the same spirit than CASSANDRA-3707.
> # add events notification on schema change.
> Just to be clear, the goal is only to inform that a change has occured, the client would
still have to query the system table to know the exact content of the change, but at least
it'll know when to do such query.

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