日志文件包含这些详细信息。memtables的时间和原因，以及压缩何时运行。但是压缩只是在任何可能的时候运行，比如在大小上是分层的，只要有4个或更多类似大小的sstables不是对某个事件的响应，所以不会记录原因，它只是不断地检查要做的事情。
在debug.log中：

DEBUG [CompactionExecutor:2] 2018-08-31 00:53:27,376 CompactionTask.java:158 - Compacting (2e443b10-ace2-11e8-8bf9-5914dc23286d) [/Users/clohfink/git/cassandra/tmp/data/system_schema/keyspaces-abac5682dea631c5b535b3d6cffd0fb6/na-8-big-Data.db:level=0, /Users/clohfink/git/cassandra/tmp/data/system_schema/keyspaces-abac5682dea631c5b535b3d6cffd0fb6/na-5-big-Data.db:level=0, /Users/clohfink/git/cassandra/tmp/data/system_schema/keyspaces-abac5682dea631c5b535b3d6cffd0fb6/na-6-big-Data.db:level=0, /Users/clohfink/git/cassandra/tmp/data/system_schema/keyspaces-abac5682dea631c5b535b3d6cffd0fb6/na-7-big-Data.db:level=0, ]
DEBUG [CompactionExecutor:2] 2018-08-31 00:53:27,448 CompactionTask.java:256 - Compacted (2e443b10-ace2-11e8-8bf9-5914dc23286d) 4 sstables to [/Users/clohfink/git/cassandra/tmp/data/system_schema/keyspaces-abac5682dea631c5b535b3d6cffd0fb6/na-9-big,] to level=0.  0.608KiB to 0.266KiB (~43% of original) in 65ms.  Read Throughput = 9.288KiB/s, Write Throughput = 4.055KiB/s, Row Throughput = ~12/s.  8 total partitions merged to 6.  Partition merge counts were {1:5, 3:1, }  

DEBUG [PerDiskMemtableFlushWriter_0:4] 2018-08-31 00:59:30,493 Memtable.java:453 - Writing Memtable-prepared_statements@841944213(0.474KiB serialized bytes, 4 ops, 0%/0% of on/off-heap limit), flushed range = (min(-9223372036854775808), max(9223372036854775807)]                                                  
DEBUG [PerDiskMemtableFlushWriter_0:4] 2018-08-31 00:59:30,493 Memtable.java:483 - Completed flushing /Users/clohfink/git/cassandra/tmp/data/system/prepared_statements-18a9c2576a0c3841ba718cd529849fef/na-2-big-Data.db (0.392KiB) for commitlog position CommitLogPosition(segmentId=1535694804718, position=5997190)