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https://issues.apache.org/jira/browse/CASSANDRA-13418?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16135028#comment-16135028
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mck edited comment on CASSANDRA-13418 at 8/21/17 10:55 AM:
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[~rgerard],
Initial review comments:
- {{CHANGES.txt}} needs a line
- is this suitable for 3.11.x as well? (Does it constitute a stability patch?
i think so, but that's an opinion)
- is the method {{TWCSCompactionController.getFullyExpiredSSTables(..)}}
really needed? (CompactionController:170 seems to do what we need already, or
am i missing something?)
- {{CompactionController.ignoreOverlaps()}} is a bit of a concept, it deserves
some apidoc love.
Trivial stuff…
- CompactionController:108 missing space in {{if(}}, same on :170
- CompactionController:232 any reason not to return an immutable set?
- TWCSCompactionController:29 needs a blank line after
- TWCSCompactionController:33 java declaration order. (static fields go before
member fields)
- TimeWindowCompactionStrategy:70 missing space in {{if(}}
was (Author: michaelsembwever):
[~rgerard],
Initial review comments:
- {{CHANGES.txt}} needs a line
- is this suitable for 3.11.x as well? (Does it constitute a stability patch?
i think so, but that's an opinion)
- is the method {{TWCSCompactionController.getFullyExpiredSSTables(..)}}
really needed? (CompactionController:170 seems to do what we need already)
- {{CompactionController.ignoreOverlaps()}} is a bit of a concept, it deserves
some apidoc love.
Trivial stuff…
- CompactionController:108 missing space in {{if(}}, same on :170
- CompactionController:232 any reason not to return an immutable set?
- TWCSCompactionController:29 needs a blank line after
- TWCSCompactionController:33 java declaration order. (static fields go before
member fields)
- TimeWindowCompactionStrategy:70 missing space in {{if(}}
> Allow TWCS to ignore overlaps when dropping fully expired sstables
> ------------------------------------------------------------------
>
> Key: CASSANDRA-13418
> URL: https://issues.apache.org/jira/browse/CASSANDRA-13418
> Project: Cassandra
> Issue Type: Improvement
> Components: Compaction
> Reporter: Corentin Chary
> Labels: twcs
> Attachments: twcs-cleanup.png
>
>
> http://thelastpickle.com/blog/2016/12/08/TWCS-part1.html explains it well. If
> you really want read-repairs you're going to have sstables blocking the
> expiration of other fully expired SSTables because they overlap.
> You can set unchecked_tombstone_compaction = true or tombstone_threshold to a
> very low value and that will purge the blockers of old data that should
> already have expired, thus removing the overlaps and allowing the other
> SSTables to expire.
> The thing is that this is rather CPU intensive and not optimal. If you have
> time series, you might not care if all your data doesn't exactly expire at
> the right time, or if data re-appears for some time, as long as it gets
> deleted as soon as it can. And in this situation I believe it would be really
> beneficial to allow users to simply ignore overlapping SSTables when looking
> for fully expired ones.
> To the question: why would you need read-repairs ?
> - Full repairs basically take longer than the TTL of the data on my dataset,
> so this isn't really effective.
> - Even with a 10% chances of doing a repair, we found out that this would be
> enough to greatly reduce entropy of the most used data (and if you have
> timeseries, you're likely to have a dashboard doing the same important
> queries over and over again).
> - LOCAL_QUORUM is too expensive (need >3 replicas), QUORUM is too slow.
> I'll try to come up with a patch demonstrating how this would work, try it on
> our system and report the effects.
> cc: [~adejanovski], [~rgerard] as I know you worked on similar issues already.
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