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From "Jan Van Besien (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-4844) Coprocessor hooks for log rolling
Date Tue, 30 Oct 2012 08:52:13 GMT

    [ https://issues.apache.org/jira/browse/HBASE-4844?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13486745#comment-13486745

Jan Van Besien commented on HBASE-4844:

I have a use case which would benefit from this feature as well.

In a coprocessor, I want to do some "eventual execution" of actions related to Puts/Deletes
on HBase. The actions should be executed "at least once" and should only execute if the actual
HBase operation was succesful.

I can use regular coprocessor functionality to get notified of Puts and Deletes etc, but this
doesn't give me guaranteed (eventual) execution of my actions because the region server might
go down in between the HLog write and the coprocessor being called.

So to solve this problem, I want to read from the HLog files. This will give me a guarantee
that I "see" everything that happened on HBase.

In a way it is very similar to how HBase replication works. So I can also translate my needs
like this: "what functionality would be required for coprocessors such that HBase replication
can be implemented as a coprocessor rather than 'in' HBase".
> Coprocessor hooks for log rolling
> ---------------------------------
>                 Key: HBASE-4844
>                 URL: https://issues.apache.org/jira/browse/HBASE-4844
>             Project: HBase
>          Issue Type: New Feature
>    Affects Versions: 0.94.0
>            Reporter: Lars Hofhansl
>            Priority: Minor
> In order to eventually do point in time recovery we need a way to reliably back up the
logs. Rather than adding some hard coded changes, we can provide coprocessor hooks and folks
can implement their own policies.

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