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From "Andrew Purtell (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-4477) Ability for an application to store metadata into the transaction log
Date Sat, 24 Sep 2011 16:19:26 GMT

    [ https://issues.apache.org/jira/browse/HBASE-4477?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13114003#comment-13114003
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Andrew Purtell commented on HBASE-4477:
---------------------------------------

We created the WALObserver coprocessor for this use case. You can build this simply and unobtrusively
with a RegionObserver to get the attributes on the Put and so something with them, like add
to the KV; and then a WALObserver can take application actions according to the added metadata
or otherwise filter it out so it doesn't affect core.

So my question is why does this need to be in core? Is the WALObserver insufficient? Is this
for <= 0.90?

> Ability for an application to store metadata into the transaction log
> ---------------------------------------------------------------------
>
>                 Key: HBASE-4477
>                 URL: https://issues.apache.org/jira/browse/HBASE-4477
>             Project: HBase
>          Issue Type: Improvement
>            Reporter: dhruba borthakur
>            Assignee: dhruba borthakur
>         Attachments: hlogMetadata1.txt
>
>
> mySQL allows an application to store an arbitrary blob along with each transaction in
its transaction logs. This JIRA is to have a similar feature request for HBASE.
> The use case is as follows: An application on one data center A stores a blob of data
along with each transaction. A replication software picks up these blobs from the transaction
logs in A and hands it to another instance of the same application running on a remote data
center B. The application in B is responsible for applying this to the remote Hbase cluster
(and also handle conflict resolution if any).

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