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From Jeff Jirsa <jji...@gmail.com>
Subject Re: Tombstones not getting purged
Date Thu, 20 Jun 2019 05:01:59 GMT
Probably overlapping sstables

Which compaction strategy?


> On Jun 19, 2019, at 9:51 PM, Léo FERLIN SUTTON <lferlin@mailjet.com.invalid> wrote:
> 
> I have used the following command to check if I had droppable tombstones :
> `/usr/bin/sstablemetadata --gc_grace_seconds 259200 /var/lib/cassandra/data/stats/tablename/md-sstablename-big-Data.db`
> 
> I checked every sstable in a loop and had 4 sstables with droppable tombstones : 
> 
> ```
> Estimated droppable tombstones: 0.1558453651124074
> Estimated droppable tombstones: 0.20980847354256815
> Estimated droppable tombstones: 0.30826566640798975
> Estimated droppable tombstones: 0.45150604672159905
> ```
> 
> I changed my compaction configuration this morning (via JMX) to force a tombstone compaction.
These are my settings on this node :
> 
> ```
> {
> "max_threshold":"32",
> "min_threshold":"4",
> "unchecked_tombstone_compaction":"true",
> "tombstone_threshold":"0.1",
> "class":"org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy"
> }
> ```
> The threshold is lowed than the amount of tombstones in these sstables and I expected
the setting `unchecked_tombstone_compaction=True` would force cassandra to run a "Tombstone
Compaction", yet about 24h later all the tombstones are still there.
> 
> ## About the cluster : 
> 
> The compaction backlog is clear and here are our cassandra settings : 
> 
> Cassandra 3.0.18
> concurrent_compactors: 4
> compaction_throughput_mb_per_sec: 150
> sstable_preemptive_open_interval_in_mb: 50
> memtable_flush_writers: 4
> 
> 
> Any idea what I might be missing ?
> 
> Regards,
> 
> Leo

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