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https://issues.apache.org/jira/browse/CASSANDRA-7819?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14106853#comment-14106853
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Benedict commented on CASSANDRA-7819:
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Hmm. Yes, it looks like this _isn't_ safe with parallel compaction. However we
can make it safe by simply making the variable volatile.
> In progress compactions should not prevent deletion of stale sstables
> ---------------------------------------------------------------------
>
> Key: CASSANDRA-7819
> URL: https://issues.apache.org/jira/browse/CASSANDRA-7819
> Project: Cassandra
> Issue Type: Improvement
> Components: Core
> Reporter: Benedict
> Assignee: Benedict
> Priority: Minor
> Labels: compaction
> Fix For: 2.0.10
>
> Attachments: 7819.txt
>
>
> Compactions retain references to potentially many sstables that existed when
> they were started but that are now obsolete; many concurrent compactions can
> compound this dramatically, and with very large files in size tiered
> compaction it is possible to inflate disk utilisation dramatically beyond
> what is necessary.
> I propose, during compaction, periodically checking which sstables are
> obsolete and simply replacing them with the sstable that replaced it. These
> sstables are by definition only used for lookup, since we are in the process
> of obsoleting the sstables we're compacting, they're only used to reference
> overlapping ranges which may be covered by tombstones.
> A simplest solution might even be to simply detect obsoletion and recalculate
> our overlapping tree afresh. This is a pretty quick operation in the grand
> scheme of things, certainly wrt compaction, so nothing lost to do this at the
> rate we obsolete sstables.
> See CASSANDRA-7139 for original discussion of the problem.
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