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From "Benedict (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-8414) Avoid loops over array backed iterators that call iter.remove()
Date Tue, 09 Dec 2014 11:43:12 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-8414?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14239312#comment-14239312
] 

Benedict commented on CASSANDRA-8414:
-------------------------------------

We should integrate this for 2.1 also, since this behaviour is exhibited still, just not in
compaction. In 2.1 we should use System.arraycopy and removed.nextSetBit though, as the performance
will be improved, particularly for sparse removes.

> Avoid loops over array backed iterators that call iter.remove()
> ---------------------------------------------------------------
>
>                 Key: CASSANDRA-8414
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-8414
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Core
>            Reporter: Richard Low
>            Assignee: Jimmy MÃ¥rdell
>              Labels: performance
>             Fix For: 2.1.3
>
>         Attachments: cassandra-2.0-8414-1.txt
>
>
> I noticed from sampling that sometimes compaction spends almost all of its time in iter.remove()
in ColumnFamilyStore.removeDeletedStandard. It turns out that the cf object is using ArrayBackedSortedColumns,
so deletes are from an ArrayList. If the majority of your columns are GCable tombstones then
this is O(n^2). The data structure should be changed or a copy made to avoid this.



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