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https://issues.apache.org/jira/browse/CASSANDRA-13418?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16000735#comment-16000735
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Romain GERARD edited comment on CASSANDRA-13418 at 5/10/17 7:32 AM:
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I am trying things out by merging your ideas [~iksaif], [~jjirsa],
[~adejanovski]
https://github.com/erebe/cassandra/commit/f70b1efa5e2b589a5d4fa7245cd307b693ca701c
but I am not sure of what to do if one node of the ring has not activated
cassadra with -Dcassandra.unsafe.xxx
https://github.com/erebe/cassandra/commit/12f085a53df62361f2fad5c046dc770ff746b417#diff-e8e282423dcbf34d30a3578c8dec15cdR101
for now I just disable it with a warning even if the compactionParams says
otherwise.
Let me know if this is not the right direction for you
was (Author: rgerard):
I am trying things out by merging your ideas [~iksaif], [~jjirsa],
[~adejanovski]
https://github.com/erebe/cassandra/commit/12f085a53df62361f2fad5c046dc770ff746b417
but I am not sure of what to do if one node of the ring has not activated
cassadra with -Dcassandra.unsafe.xxx
https://github.com/erebe/cassandra/commit/12f085a53df62361f2fad5c046dc770ff746b417#diff-e8e282423dcbf34d30a3578c8dec15cdR101
for now I just disable it with a warning even if the compactionParams says
otherwise.
Let me know if this is not the right direction for you
> 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
>
> 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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