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https://issues.apache.org/jira/browse/CASSANDRA-6109?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13790610#comment-13790610
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Jonathan Ellis commented on CASSANDRA-6109:
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I'm thinking about how I tune this as an operator. If we're going by
coldness-relative-to-mean, I'm not really sure where to set that to achieve my
read performance goals other than trial and error.
Suppose for instance that I have 11 sstables, one of which has 10M reads
recently and 10 of which have 1M reads. If I set my threshold to 25% then
nothing gets compacted which is probably not what we want, since the 10 "cold"
sstables collectively represent 50% of the read activity.
What if instead we
# analyze hotness globally (per-CF) rather than per-bucket, and
# configure the threshold based on hotness percentile (compact me if I am
hotter than N% of my peers)
> Consider coldness in STCS compaction
> ------------------------------------
>
> Key: CASSANDRA-6109
> URL: https://issues.apache.org/jira/browse/CASSANDRA-6109
> Project: Cassandra
> Issue Type: New Feature
> Components: Core
> Reporter: Jonathan Ellis
> Assignee: Tyler Hobbs
> Fix For: 2.0.2
>
> Attachments: 6109-v1.patch, 6109-v2.patch
>
>
> I see two options:
> # Don't compact cold sstables at all
> # Compact cold sstables only if there is nothing more important to compact
> The latter is better if you have cold data that may become hot again... but
> it's confusing if you have a workload such that you can't keep up with *all*
> compaction, but you can keep up with hot sstable. (Compaction backlog stat
> becomes useless since we fall increasingly behind.)
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