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From "Milan Majercik (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-12796) Heap exhaustion when rebuilding secondary index over a table with wide partitions
Date Mon, 12 Dec 2016 09:25:58 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-12796?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15741428#comment-15741428
] 

Milan Majercik commented on CASSANDRA-12796:
--------------------------------------------

[~beobal], sorry for delay in response. Just tested your fix on our sample data and it works
fine. Thank you for your help.

> Heap exhaustion when rebuilding secondary index over a table with wide partitions
> ---------------------------------------------------------------------------------
>
>                 Key: CASSANDRA-12796
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-12796
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Core
>            Reporter: Milan Majercik
>            Priority: Critical
>
> We have a table with rather wide partition and a secondary index defined over it. As
soon as we try to rebuild the index we observed exhaustion of Java heap and eventual OOM error.
After a lengthy investigation we have managed to find a culprit which appears to be a wrong
granule of barrier issuances in method {{org.apache.cassandra.db.Keyspace.indexRow}}:
> {code}
>         try (OpOrder.Group opGroup = cfs.keyspace.writeOrder.start()){html}
>         {
>             Set<SecondaryIndex> indexes = cfs.indexManager.getIndexesByNames(idxNames);
>             Iterator<ColumnFamily> pager = QueryPagers.pageRowLocally(cfs, key.getKey(),
DEFAULT_PAGE_SIZE);
>             while (pager.hasNext())
>             {
>                 ColumnFamily cf = pager.next();
>                 ColumnFamily cf2 = cf.cloneMeShallow();
>                 for (Cell cell : cf)
>                 {
>                     if (cfs.indexManager.indexes(cell.name(), indexes))
>                         cf2.addColumn(cell);
>                 }
>                 cfs.indexManager.indexRow(key.getKey(), cf2, opGroup);
>             }
>         }
> {code}
> Please note the operation group granule is a partition of the source table which poses
a problem for wide partition tables as flush runnable ({{org.apache.cassandra.db.ColumnFamilyStore.Flush.run()}})
won't proceed with flushing secondary index memtable before completing operations prior recent
issue of the barrier. In our situation the flush runnable waits until whole wide partition
gets indexed into the secondary index memtable before flushing it. This causes an exhaustion
of the heap and eventual OOM error.
> After we changed granule of barrier issue in method {{org.apache.cassandra.db.Keyspace.indexRow}}
to query page as opposed to table partition secondary index (see [https://github.com/mmajercik/cassandra/commit/7e10e5aa97f1de483c2a5faf867315ecbf65f3d6?diff=unified]),
rebuild started to work without heap exhaustion. 



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