Correct. Why are you concerned with the raw throughput, are you accumulating pending compactions? Are you seeing high sstables per read statistics?
all the best, Sebastián On Jan 15, 2016 6:18 PM, "Kai Wang" <dep...@gmail.com> wrote: > Jeff & Sebastian, > > Thanks for the reply. There are 12 cores but in my case C* only uses one > core most of the time. *nodetool compactionstats* shows there's only one > compactor running. I can see C* process only uses one core. So I guess I > should've asked the question more clearly: > > 1. Is ~25 M/s a reasonable compaction throughput for one core? > 2. Is there any configuration that affects single core compaction > throughput? > 3. Is concurrent_compactors the only option to parallelize compaction? If > so, I guess it's the compaction strategy itself that decides when to > parallelize and when to block on one core. Then there's not much we can do > here. > > Thanks. > > On Fri, Jan 15, 2016 at 5:23 PM, Jeff Jirsa <jeff.ji...@crowdstrike.com> > wrote: > >> With SSDs, the typical recommendation is up to 0.8-1 compactor per core >> (depending on other load). How many CPU cores do you have? >> >> >> From: Kai Wang >> Reply-To: "user@cassandra.apache.org" >> Date: Friday, January 15, 2016 at 12:53 PM >> To: "user@cassandra.apache.org" >> Subject: compaction throughput >> >> 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. >> > >
