Hi, We have a single-node cassandra that contains volatile data: every day about 2 Gb of data is written, this data is kept for 7 days and then removed (using TTL). To avoid that the application becomes slow during a large compaction, we do a major compaction every night (less users, less performance impact).
The major compaction is CPU bound: it uses about 1 core and only consumes 4 Mb/sec disk IO. We would like to scale the compaction with the resources available in the machine (cores, disks). Enabling multithreaded_compaction didn't help a lot, the CPU usage goes up to 120% of one core, but does not scale with the number of cores. To make the compaction scale with the number of cores in our machine, we tried to perform a major compaction on multiple column families (in the same keyspace) at the same time using `nodetool -h localhost compact testSpace data1 data2`, however the 2 compactions are executed serially in stead of concurrently, with concurrent_compactors set to 4 (the number of cores). Is this normal behavior (both the multihreading and concurrent compactions) ? Is there any way to make the major compactions scale with the number of cores in the machine ? Thanks ! Frederick
