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https://issues.apache.org/jira/browse/CASSANDRA-8360?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Marcus Eriksson resolved CASSANDRA-8360.
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Resolution: Fixed
will commit fix as part of CASSANDRA-8359
> In DTCS, always compact SSTables in the same time window, even if they are
> fewer than min_threshold
> ---------------------------------------------------------------------------------------------------
>
> Key: CASSANDRA-8360
> URL: https://issues.apache.org/jira/browse/CASSANDRA-8360
> Project: Cassandra
> Issue Type: Improvement
> Reporter: Björn Hegerfors
> Assignee: Björn Hegerfors
> Priority: Minor
> Fix For: 3.0, 2.1.4, 2.0.14
>
> Attachments: cassandra-2.0-CASSANDRA-8360.txt
>
>
> DTCS uses min_threshold to decide how many time windows of the same size that
> need to accumulate before merging into a larger window. The age of an SSTable
> is determined as its min timestamp, and it always falls into exactly one of
> the time windows. If multiple SSTables fall into the same window, DTCS
> considers compacting them, but if they are fewer than min_threshold, it
> decides not to do it.
> When do more than 1 but fewer than min_threshold SSTables end up in the same
> time window (except for the current window), you might ask? In the current
> state, DTCS can spill some extra SSTables into bigger windows when the
> previous window wasn't fully compacted, which happens all the time when the
> latest window stops being the current one. Also, repairs and hints can put
> new SSTables in old windows.
> I think, and [~jjordan] agreed in a comment on CASSANDRA-6602, that DTCS
> should ignore min_threshold and compact tables in the same windows regardless
> of how few they are. I guess max_threshold should still be respected.
> [~jjordan] suggested that this should apply to all windows but the current
> window, where all the new SSTables end up. That could make sense. I'm not
> clear on whether compacting many SSTables at once is more cost efficient or
> not, when it comes to the very newest and smallest SSTables. Maybe compacting
> as soon as 2 SSTables are seen is fine if the initial window size is small
> enough? I guess the opposite could be the case too; that the very newest
> SSTables should be compacted very many at a time?
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