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From "Lars Hofhansl (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-4583) Integrate RWCC with Append and Increment operations
Date Thu, 03 Nov 2011 17:29:32 GMT

    [ https://issues.apache.org/jira/browse/HBASE-4583?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13143349#comment-13143349
] 

Lars Hofhansl commented on HBASE-4583:
--------------------------------------

The problem is that if the changes are not visible immediately there might be old scanners
still scanning the old KVs in the memstore and hence these cannot be removed.

Increment/Append/ICV currently work because all changes are visible to *all* scanners, because
only then can we safely remove the duplicates.

I now think that this:
bq. Another option would be to remove the previous KVs after you roll rwcc forward and release
the row lock, before dropping the region-level lock

Actually does not work.

In order to make this work we would need to know the lowest readpoint currently used by any
other (read) transaction and only remove duplicate KVs *before* that readpoint.
Since we do not have that information and readers also do not take out any locks, I don't
see any way of making this work.

                
> Integrate RWCC with Append and Increment operations
> ---------------------------------------------------
>
>                 Key: HBASE-4583
>                 URL: https://issues.apache.org/jira/browse/HBASE-4583
>             Project: HBase
>          Issue Type: Bug
>            Reporter: Lars Hofhansl
>            Assignee: Lars Hofhansl
>             Fix For: 0.94.0
>
>         Attachments: 4583-v2.txt, 4583-v3.txt, 4583-v4.txt, 4583.txt
>
>
> Currently Increment and Append operations do not work with RWCC and hence a client could
see the results of multiple such operation mixed in the same Get/Scan.
> The semantics might be a bit more interesting here as upsert adds and removes to and
from the memstore.

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