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From "stack (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-2283) row level atomicity
Date Fri, 19 Mar 2010 00:24:27 GMT

    [ https://issues.apache.org/jira/browse/HBASE-2283?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12847168#action_12847168
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stack commented on HBASE-2283:
------------------------------

Patch looks good.  Applied to 0.20 branch.  Had to mess in transactional hbase to make it
use new WALEdit rather than KeyValue as HLog value.   Working on forward port to TRUNK.

> 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, rowLevelAtomicity_2283_v2.patch,
rowLevelAtomicity_2283_v3.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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