Same here. We disable the throttling and our disk and CPU usage both low (< 10%) and still takes hours for LCS compaction to finish after a repair. For this cluster, we don't delete any data, so we can rule out tombstones. Not sure what is holding compaction back. My observation is that for the LCS which involves large number of SSTables (since we set SSTable size too small at 10M and sometimes one compactions involves up to 10 G of data = 1000 SSTables), the throughout put is smaller. So my theory is that open/close file handlers have substantial impact on the throughput.
By the way, we are on SSD. -Wei ________________________________ From: "Hiller, Dean" <dean.hil...@nrel.gov> To: "user@cassandra.apache.org" <user@cassandra.apache.org> Sent: Wednesday, April 24, 2013 1:37 PM Subject: Re: compaction throughput rate not even close to 16MB Thanks much!!! Better to hear at least one other person sees the same thing ;). Sometimes these posts just go silent. Dean From: Edward Capriolo <edlinuxg...@gmail.com<mailto:edlinuxg...@gmail.com>> Reply-To: "user@cassandra.apache.org<mailto:user@cassandra.apache.org>" <user@cassandra.apache.org<mailto:user@cassandra.apache.org>> Date: Wednesday, April 24, 2013 2:33 PM To: "user@cassandra.apache.org<mailto:user@cassandra.apache.org>" <user@cassandra.apache.org<mailto:user@cassandra.apache.org>> Subject: Re: compaction throughput rate not even close to 16MB I have noticed the same. I think in the "real" world your compaction throughput is limited by other things. If I had to speculate I would say that compaction can remove expired tombstones, however doing this requires bloom filter checks, etc. I think that setting is more important with multi threaded compaction and/or more compaction slots. In those cases it may actually throttle something. On Wed, Apr 24, 2013 at 3:54 PM, Hiller, Dean <dean.hil...@nrel.gov<mailto:dean.hil...@nrel.gov>> wrote: I was wondering about the compactionthroughput. I never see ours get even close to 16MB and I thought this is supposed to throttle compaction, right? Ours is constantly less than 3MB/sec from looking at our logs or do I have this totally wrong? How can I see the real throughput so that I can understand how to throttle it when I need to? 94,940,780 bytes to 95,346,024 (~100% of original) in 38,438ms = 2.365603MB/s. 2,350,114 total rows, 2,350,022 unique. Row merge counts were {1:2349930, 2:92, } Thanks, Dean
