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From "Kannan Muthukkaruppan (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-2283) row level atomicity
Date Mon, 15 Mar 2010 23:18:27 GMT

    [ https://issues.apache.org/jira/browse/HBASE-2283?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12845589#action_12845589
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Kannan Muthukkaruppan commented on HBASE-2283:
----------------------------------------------

Found the issue with TestGetClosestAtOrBefore:testUsingMetaAndBinary() failures. It was indeed
due to my patch :(.

During a put(), updateKeys() is called to convert the special "LATEST" timestamp to "now".
My patch had the inadvertent side effect of calling updateKeys() inside of the if (writeToWAL)
check instead of doing so always. This particular test passes "false" for writeToWAL, and
so the puts ended up having LATEST timestamps, as their timestamps never got adjusted. This
causes subsequent deletes with "now" timestamps to become no-ops. 

 

> row level atomicity 
> --------------------
>
>                 Key: HBASE-2283
>                 URL: https://issues.apache.org/jira/browse/HBASE-2283
>             Project: Hadoop HBase
>          Issue Type: Bug
>            Reporter: Kannan Muthukkaruppan
>            Priority: Blocker
>             Fix For: 0.20.4, 0.21.0
>
>         Attachments: rowLevelAtomicity_2283_v1.patch
>
>
> The flow during a HRegionServer.put() seems to be the following. [For now, let's just
consider single row Put containing edits to multiple column families/columns.]
> HRegionServer.put() does a:
>         HRegion.put();
>        syncWal()  (the HDFS sync call).  /* this is assuming we have HDFS-200 */
> HRegion.put() does a:
>   for each column family 
>   {
>       HLog.append(all edits to the colum family);
>       write all edits to Memstore;
>   }
> HLog.append() does a :
>   foreach edit in a single column family {
>     doWrite()
>   }
> doWrite() does a:
>    this.writer.append().
> There seems to be two related issues here that could result in inconsistencies.
> Issue #1: A put() does a bunch of HLog.append() calls. These in turn do a bunch of "write"
calls on the underlying DFS stream.  If we crash after having written out some append's to
DFS, recovery will run and apply a partial transaction to memstore.  
> Issue #2: The updates to memstore  should happen after the sync rather than before. Otherwise,
there is the danger that the write to DFS (sync) fails for some reason & we return an
error to the client, but we have already taken edits to the memstore. So subsequent reads
will serve uncommitted data.

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