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From "Michael Gottesman (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-1090) Atomic Check And Save in HTable
Date Tue, 06 Jan 2009 09:15:44 GMT

    [ https://issues.apache.org/jira/browse/HBASE-1090?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12661084#action_12661084
] 

Michael Gottesman commented on HBASE-1090:
------------------------------------------

So I went through it and found the issue. The problem that seemed to be happening had to do
with me returning false in the middle of the checkAndSave in HRegion/releasing locks in the
middle of the checkAndSave in HRegion. Instead of doing that, I created a variable that just
said whether or not the expected values matched up and then if it doesn't skips the save part
of check and save. Then in the typical HBase fashion the locks are released and a value is
returned after all of the try blocks have closed.

Attached is the new patch.

> Atomic Check And Save in HTable
> -------------------------------
>
>                 Key: HBASE-1090
>                 URL: https://issues.apache.org/jira/browse/HBASE-1090
>             Project: Hadoop HBase
>          Issue Type: New Feature
>            Reporter: Michael Gottesman
>            Priority: Minor
>         Attachments: 1090v3.patch, 1090v4.patch, hbase-1090.patch, hbase-1090v2.patch
>
>
> Check And Save is a simple operation where one gives both a BatchUpdate with updates
and a Map mapping columns to expected values (byte[] -> byte[]). The operation works as
follows:
> 1. Server gets locks on row.
> 2. Server checks that the actual values of the specified columns match the given expected
values
> 3. If False, return False, if True update the row
> 4. Unlock row.
> Pretty simple... but useful.
> Included in the attached patch are the necessary updates for HTable, HRegionServer, RegionServerInterface,
and HRegion. I also added a small unit test to HTable where the test checks that checkAndSave
succeeds when the expected values line up and fail when the values are different.

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