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https://issues.apache.org/jira/browse/HBASE-2283?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Kannan Muthukkaruppan updated HBASE-2283:
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Attachment: rowLevelAtomicity_2283_v3.patch
A small one line improvement to v2 patch based on internal feedback. The change
makes it so that if someone reuses an instance of WALEdit across multiple calls
to the sequence file reader, the readFields() method cleans out any old state
of the object cleanly.
> 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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