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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-2231) Compaction events should be written to HLog
Date Wed, 19 May 2010 22:41:54 GMT

    [ https://issues.apache.org/jira/browse/HBASE-2231?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12869386#action_12869386
] 

Todd Lipcon commented on HBASE-2231:
------------------------------------

I've been thinking about this a bit, and I want to think about a different design.

The flaw with the design as I outlined above is that we have to read through the entire reconstruction
HLog until we find the special entries telling us to "finish off" the compaction for the dead
regionserver. This is fine in today's world, but I think in some instances it would be better
to finish the compaction and get the directory in a reasonable state *before* replaying the
logs. This would allow, for example, the recovering regionserver to start serving the region
in "stale readonly" mode before log replay is done.

I'm thinking about a different design in which we add an /hbase/ops-in-progress/regionserver/
directory in zookeeper. When we are about to start moving files around after a compaction,
we write our intention in there, and when we're done, we remove it. Thus the HMaster can take
of finishing or aborting the compaction immediately when it starts recovery, and the recovering
regionserver doesn't have to worry about the transition in progress.

Thoughts?

> Compaction events should be written to HLog
> -------------------------------------------
>
>                 Key: HBASE-2231
>                 URL: https://issues.apache.org/jira/browse/HBASE-2231
>             Project: Hadoop HBase
>          Issue Type: Improvement
>          Components: regionserver
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>             Fix For: 0.21.0
>
>         Attachments: hbase-2231-testcase.txt, hbase-2231.txt
>
>
> The sequence for a compaction should look like this:
> # Compact region to "new" files
> # Write a "Compacted Region" entry to the HLog
> # Delete "old" files
> This deals with a case where the RS has paused between step 1 and 2 and the regions have
since been reassigned.

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