[ https://issues.apache.org/jira/browse/CASSANDRA-13418?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16066894#comment-16066894 ]
Romain GERARD edited comment on CASSANDRA-13418 at 6/28/17 5:21 PM: -------------------------------------------------------------------- Hi back Marcus, So I took into account your comments and regarding your the 1rst one I wanted to do that at first but getFullyExpiredSSTables is also used in [CompactionTask|https://github.com/criteo-forks/cassandra/blob/trunk/src/java/org/apache/cassandra/db/compaction/CompactionTask.java#L165] So only modifying things at the TWS level would have resulted in compacting the sstables that we wanted to drop, and I was not too incline to touch to CompactionTask. It is also making worthDroppingTombstones [ignoring overlaps|https://github.com/criteo-forks/cassandra/blob/trunk/src/java/org/apache/cassandra/db/compaction/TimeWindowCompactionStrategy.java#L141] and respect the tombstoneThresold specified (We can turn on uncheckedTombstoneCompaction for this one) Regarding the 2nd question I put the code validating the options in [TimeWindowCompactionStategyOptions|https://github.com/criteo-forks/cassandra/blob/cassandra-3.11-criteo/src/java/org/apache/cassandra/db/compaction/TimeWindowCompactionStrategyOptions.java#L157] in order to [trigger an exception|https://github.com/criteo-forks/cassandra/blob/cassandra-3.11-criteo/src/java/org/apache/cassandra/schema/CompactionParams.java#L161] if the options is used elsewhere than TWCS. P.s: I will have more time in the upcoming days, so I will be more responsive. was (Author: rgerard): Hi back Marcus, So I took into account your comments and regarding your the 1rst one I wanted to do that at first but getFullyExpiredSSTables is also used in [CompactionTask|https://github.com/criteo-forks/cassandra/blob/trunk/src/java/org/apache/cassandra/db/compaction/CompactionTask.java#L165] So only modifying things at the TWS level would have resulted in compacting the sstables that we wanted to drop, and I was not too incline to touch to CompactionTask. It is also making worthDroppingTombstones [ignoring overlaps|https://github.com/criteo-forks/cassandra/blob/trunk/src/java/org/apache/cassandra/db/compaction/TimeWindowCompactionStrategy.java#L141] and respect the tombstoneThresold specified (We can turn on uncheckedTombstoneCompaction for this one) Regarding the 2nd question I put the code validating the options in TimeWindowCompactionStategyOptions https://github.com/criteo-forks/cassandra/blob/cassandra-3.11-criteo/src/java/org/apache/cassandra/db/compaction/TimeWindowCompactionStrategyOptions.java#L157 in order to trigger an exception if the options is used elsewhere than TWCS. https://github.com/criteo-forks/cassandra/blob/cassandra-3.11-criteo/src/java/org/apache/cassandra/schema/CompactionParams.java#L161 P.s: I will have more time in the upcoming days, so I will be more responsive. > 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