> > With STCS, estimated droppable tombstones being always 0.0 (thus also no > automatic single SSTable compaction may happen): Is this a matter of not > writing with TTL? If yes, would enabling TTL with STCS improve the disk > reclaim situation, cause then single SSTAble compactions will kick in?
Estimated droppable tombstones will increase if you have tombstones in an SSTable. It is just an estimate however, but if you are deleting in any way (TTL or manual) it should increase. Enabling TTL would increase disk reclaim, but only because you would be deleting more data. Doing so only makes sense if you actually can TTL your data. Probably don't do that without fully understanding all the potential impacts to your data. In fact it's not a great idea with STCS anyway. Also, single SSTable compactions aren't very good for removing tombstones anyway so probably shouldn't be relied on. To get rid of a tombstone the tombstone needs to be compacted with every other SSTable that contains data the tombstone covers. What is the semantic of “default_time_to_live” at table level? From: > http://docs.datastax.com/en/cql/3.1/cql/cql_using/use_expire_c.html : > “After the default_time_to_live TTL value has been exceed, Cassandra > tombstones the entire table”. What does “entire table” mean? Hopefully / I > guess I don’t end up with an empty table every X past TTLs? I didn't read that page but Cassandra doesn't tombstone the entire table. If the default TTL is set on the table, then whenever any data inserted into the table surpasses the TTL it is becomes expired (essentially a tombstone). You won't end up with an empty table unless you stop inserting data. I know, changing compaction is a matter of executing ALTER TABLE (or > temporary via JMX for a single node), but as we have legacy data being > written without TTL, I wonder if we may end up in stuck SSTable again Yes, if you have legacy data you should make sure you delete it before you change compaction strategy to TWCS. Otherwise you may have SSTables with live data that never get deleted. Short on time, sorry I didn't answer all your questions!
