On Wed, Jul 9, 2014 at 4:27 PM, Andrew <redmu...@gmail.com> wrote: > What kind of overhead should I expect for compaction, in terms of size? > In this use case, the primary use for compaction is more or less to clean > up tombstones for expired TTLs. >
Compaction can result in output files >100% of the input, if compression is used and the input SSTables are also compressed. If you use size tiered compaction (STS), you therefore must have enough headroom to compact your largest [n] SSTables together successfully. Level compaction (LCS) has a different, significantly lower, amount of headroom. If you are making heavy use of TTL, you should be careful about using LCS in certain cases, read : https://issues.apache.org/jira/browse/CASSANDRA-6654 - "Droppable tombstones are not being removed from LCS table despite being above 20%" =Rob
