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From Anuj Wadehra <>
Subject Evict Tombstones with STCS
Date Sat, 28 May 2016 19:24:56 GMT
We are using C* 2.0.x . What options are available if disk space is too full to do compaction
on huge sstables formed by STCS (created around long ago but not getting compacted due to
min_compaction_threshold being 4).
We suspect that huge space will be released when 2 largest sstables get compacted together
such that tombstone eviction is possible. But there is not enough space for compacting them
together assuming that compaction would need at least free disk=size of sstable1 + size of
sstable 2 ??
I read STCS code and if no sstables are available for compactions, it should pick individual
sstable for compaction. But somehow, huge sstables are not participating in individual compaction..
is it due to default 20% tombstone threshold?? And if it so, forceUserdefinedcompaction or
setting unchecked_tombstone_compactions to true wont help either as tombstones are less than
20% and not much disk would be recovered.
It is not possible to add additional disks too.
We see huge difference in disk utilization of different nodes. May be some nodes were able
to get away with tombstones while others didnt manage to evict tombstones.

Would be good to know more alternatives from community.


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