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From "Jonathan Ellis (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-8414) Avoid loops over array backed iterators that call iter.remove()
Date Sat, 06 Dec 2014 02:55:14 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-8414?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14236527#comment-14236527
] 

Jonathan Ellis commented on CASSANDRA-8414:
-------------------------------------------

/cc [~slebresne]

> 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
>              Labels: performance
>             Fix For: 2.1.3
>
>
> 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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