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https://issues.apache.org/jira/browse/CASSANDRA-8414?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14236760#comment-14236760
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Aleksey Yeschenko commented on CASSANDRA-8414:
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Actually Richard's issue is with 1.2 and 2.0.
I'm not sure how much of an issue in practice it really is for compaction in
2.1, w/ only LazilyCompactedRow there, and PreCompactedRow gone.
> 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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