Compaction is generally CPU bound and relatively slow. Exactly why that is I’m uncertain.
> On Jan 15, 2016, at 12:53 PM, Kai Wang <dep...@gmail.com> wrote: > > Hi, > > I am trying to figure out the bottleneck of compaction on my node. The node > is CentOS 7 and has SSDs installed. The table is configured to use LCS. Here > is my compaction related configs in cassandra.yaml: > > compaction_throughput_mb_per_sec: 160 > concurrent_compactors: 4 > > I insert about 10G of data and start observing compaction. > > nodetool compaction shows most of time there is one compaction. Sometimes > there are 3-4 (I suppose this is controlled by concurrent_compactors). During > the compaction, I see one CPU core is 100%. At that point, disk IO is about > 20-25 M/s write which is much lower than the disk is capable of. Even when > there are 4 compactions running, I see CPU go to +400% but disk IO is still > at 20-25M/s write. I use nodetool setcompactionthroughput 0 to disable the > compaction throttle but don't see any difference. > > Does this mean compaction is CPU bound? If so 20M/s is kinda low. Is there > anyway to improve the throughput? > > Thanks.
