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https://issues.apache.org/jira/browse/HBASE-669?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12623580#action_12623580
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Clint Morgan commented on HBASE-669:
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When replaying a hlog, we need to track transaction start, write, commit, and
abort messages and react appropriately. This contrasts with the normal logic of
simply replaying HLog edits at the hstore level. I have this logic in place
(see changes to HLog, HLogEdit, HLogKey), but have not fully tested it. There
are a couple of tricky/sublte issues there that I'm not sure I've gotten right.
EG, the min sequence number that we have to look at for recovery is not simply
that of the last flush. Rather it depends on the min seq numbers of the start
messages of pending transactions at the time of hlog flush...
Also, if we crash at just the right time, we could have committed pieces of a
transaction in other regions, but not have the commit message in the log for
this region. In this case, we need to lookup the transaction state
(commited/aborted) in a global transaction log. I'd like to put this global
transaction log in Zookeper when its in the mix.
> MultiRegion transactions with Optimistic Concurrency Control
> ------------------------------------------------------------
>
> Key: HBASE-669
> URL: https://issues.apache.org/jira/browse/HBASE-669
> Project: Hadoop HBase
> Issue Type: New Feature
> Components: client, ipc, regionserver
> Reporter: Clint Morgan
> Assignee: Clint Morgan
> Fix For: 0.3.0
>
> Attachments: hbase-669-v2.patch, hbase-669-v3.patch,
> hbase-669-v4.patch, hbase-669-v5.patch, hbase-669.patch, hbase-669.patch,
> hbase-669.patch
>
>
> We have a need for ACID transactions across tables. This issue is about
> adding transactions which span multiple regions. We do not envision many
> competing writes, and will be read-dominated in general. This makes
> Optimistic Concurrency Control (OCC) seem like the way to go.
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