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Romain GERARD commented on CASSANDRA-13418: ------------------------------------------- Initial review comments: * CHANGES.txt needs a line -> OK * I think so also as it greatly help having a stable behavior when using TWCS for time series * Not at all, it was just to pack things together and to inform the reader that a TWCSCompactionController exist * OK Trivial stuff : * Ok * I don't like to return Immutable collections when only the base type (Set, List, Map,...) is specified as due to the type erasure someone will get burn at runtime with that (due to unchecked exception). And also as the parent function already use a mutable set I sticked with that because returning sometime a mutable set and sometime an immutable set is kind of a leaky abstraction for me (Will check if I can change everything for an ImmutableSet) * OK * OK Will propose an other patch tomorrow. P.S: The patch has been running in production since last Friday without hickups. > 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. -- This message was sent by Atlassian JIRA (v6.4.14#64029) --------------------------------------------------------------------- To unsubscribe, e-mail: commits-unsubscr...@cassandra.apache.org For additional commands, e-mail: commits-h...@cassandra.apache.org