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 :

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 ?