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https://issues.apache.org/jira/browse/CASSANDRA-18397?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17714625#comment-17714625
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Branimir Lambov commented on CASSANDRA-18397:
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Generally density (and levels) are a proxy for time, and thus can provide some
version of this. However, one thing it can't do that appears to be important
for some workloads, is the ability to provide guarantees that deleted data will
be actually removed from the sstable set within a specified amount of time.
UCS could allow for this if we introduce a time component to the strategy. It
looks like the simplest option would be to additionally permit levelling based
on elapsed time, which would enable both TWCS-like leave-old-sstables-alone
behaviour (where old sstables move to higher levels of the hierarchy as they
age and never meet), as well as compact-all-old-sstables as described (where
old sstables stay in the same level and compaction is immediately triggered
when a new sstable matures enough to enter their bucket). I think this is well
worth doing, but I would prefer to do this after the current 5.0 push is over.
> CEP-26: Unified Compaction Strategy
> -----------------------------------
>
> Key: CASSANDRA-18397
> URL: https://issues.apache.org/jira/browse/CASSANDRA-18397
> Project: Cassandra
> Issue Type: Improvement
> Components: Local/Compaction
> Reporter: Branimir Lambov
> Assignee: Branimir Lambov
> Priority: Normal
> Time Spent: 10m
> Remaining Estimate: 0h
>
> Implementation of Unified Compaction Strategy per
> [CEP-26|https://cwiki.apache.org/confluence/display/CASSANDRA/CEP-26%3A+Unified+Compaction+Strategy].
> Further documentation of the most current state of the solution can be found
> in [the included markdown
> documentation|https://github.com/blambov/cassandra/blob/CASSANDRA-18397/src/java/org/apache/cassandra/db/compaction/UnifiedCompactionStrategy.md].
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