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From "Lars Hofhansl (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-5203) Group atomic put/delete operation into a single WALEdit to handle region server failures.
Date Mon, 16 Jan 2012 01:53:40 GMT

    [ https://issues.apache.org/jira/browse/HBASE-5203?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13186645#comment-13186645
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Lars Hofhansl commented on HBASE-5203:
--------------------------------------

Because the Delete might come before the Put or vice versa? Put and Delete are not commutative,
their order matters.
I think that is reasonable. Just like from the client you can issue Deletes and Puts in any
order for the same family.

But... Looking at Delete.java, there is some other weirdness there:
When you add a family marker for a family it deletes all column/version markers for that family,
but does not check the timestamp. When can't I issue a Delete that deletes a family F for
time T1 and some columns of that family for time T2 (when T2 > T1)?
Note that the same it true for column makers that hide version markers... In theory we could
remove the version markers too.

If that strange logic would not exist in Delete, this would become simpler. (It would incidentally
also simplify the Import/Copytable MR code).

So the first thing I propose is removing that logic in Delete.java. You can just add family/column/version
markers to a Delete as you please. If we want to be fancy we can track the latest TS for columnfamily
and then remove all entries if superseded by a family delete marker - but I do not even think
that is necessary.

                
> Group atomic put/delete operation into a single WALEdit to handle region server failures.
> -----------------------------------------------------------------------------------------
>
>                 Key: HBASE-5203
>                 URL: https://issues.apache.org/jira/browse/HBASE-5203
>             Project: HBase
>          Issue Type: Sub-task
>          Components: client, coprocessors, regionserver
>            Reporter: Lars Hofhansl
>            Assignee: Lars Hofhansl
>             Fix For: 0.94.0
>
>
> HBASE-3584 does not not provide fully atomic operation in case of region server failures
(see explanation there).
> What should happen is that either (1) all edits are applied via a single WALEdit, or
(2) the WALEdits are applied in async mode and then sync'ed together.
> For #1 it is not clear whether it is advisable to manage multiple *different* operations
(Put/Delete) via a single WAL edit. A quick check reveals that WAL replay on region startup
would work, but that replication would need to be adapted. The refactoring needed would be
non-trivial.
> #2 Might actually not work, as another operation could request sync'ing a later edit
and hence flush these entries out as well.

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