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https://issues.apache.org/jira/browse/CASSANDRA-8414?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14246961#comment-14246961
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Richard Low commented on CASSANDRA-8414:
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Thanks for writing the patch! A few comments:
- v3 patch has BatchIterator interface missing.
- Some unnecessary formatting changes and import order switching.
- remove method should throw IllegalStateException if called twice on same
element to adhere to Iterator spec.
- Calling commit twice will remove incorrect elements. Should throw
IllegalStateException if commit is called more than once or make it idempotent.
- Could add 'assert test <= src;' to copy method to enforce comment.
> 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 Mårdell
> Labels: performance
> Fix For: 2.1.3
>
> Attachments: cassandra-2.0-8414-1.txt, cassandra-2.0-8414-2.txt,
> cassandra-2.0-8414-3.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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