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Posted to issues@hbase.apache.org by "Shrijeet Paliwal (JIRA)" <ji...@apache.org> on 2012/12/15 08:50:13 UTC
[jira] [Updated] (HBASE-2283) row level atomicity
[ https://issues.apache.org/jira/browse/HBASE-2283?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Shrijeet Paliwal updated HBASE-2283:
------------------------------------
Description:
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.
was:
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.
> row level atomicity
> --------------------
>
> Key: HBASE-2283
> URL: https://issues.apache.org/jira/browse/HBASE-2283
> Project: HBase
> Issue Type: Bug
> Reporter: Kannan Muthukkaruppan
> Assignee: Kannan Muthukkaruppan
> Priority: Blocker
> Fix For: 0.90.0
>
> 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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