@penguin There have been steady improvements in the different compaction strategies recently but not major re-writes.
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On Thu, Jan 21, 2016 at 9:12 AM, Kai Wang <dep...@gmail.com> wrote: > I am using 2.2.4 and have seen multiple compactors running on the same > table. The number of compactors seems to be controlled by > concurrent_compactors. As of type of compactions, I've seen normal > compaction, tombstone compaction. Validation and Anticompaction seem to > always be single threaded. > > On Thu, Jan 21, 2016 at 8:28 AM, PenguinWhispererThe . < > th3penguinwhispe...@gmail.com> wrote: > >> Thanks for that clarification Sebastian! That's really good to know! I >> never took increasing this value in consideration because of my previous >> experience. >> >> In my case I had a table that was compacting over and over... and only >> one CPU was used. So that made me believe it was not multithreaded (I >> actually believe I asked this on IRC however it's been a few months ago so >> I might be wrong). >> >> Have there been behavioral changes on this lately? (I was using 2.0.9 or >> 2.0.11 I believe). >> >> 2016-01-21 14:15 GMT+01:00 Sebastian Estevez < >> sebastian.este...@datastax.com>: >> >>> >So compaction of one table will NOT spread over different cores. >>> >>> This is not exactly true. You actually can have multiple compactions >>> running at the same time on the same table, it just doesn't happen all that >>> often. You essentially would have to have two sets of sstables that are >>> both eligible for compactions at the same time. >>> >>> all the best, >>> >>> Sebastián >>> On Jan 21, 2016 7:41 AM, "PenguinWhispererThe ." < >>> th3penguinwhispe...@gmail.com> wrote: >>> >>>> After having some issues myself with compaction I think it's noteworthy >>>> to explicitly state that compaction of a table can only run on one CPU. So >>>> compaction of one table will NOT spread over different cores. >>>> To really have use of concurrent_compactors you need to have multiple >>>> table compactions initiated at the same time. If those are small they'll >>>> finish way earlier resulting in only one core using 100% as compaction is >>>> generally CPU bound (unless your disks can't keep up). >>>> I believe it's better to be CPU(core) bound on one core(or at least not >>>> all) for compaction than disk IO bound as this would result in writes and >>>> reads, ... having performance impact. >>>> Compaction is a maintenance task so it shouldn't be eating all your >>>> resources. >>>> >>>> >>>> <https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail> >>>> This >>>> email has been sent from a virus-free computer protected by Avast. >>>> www.avast.com >>>> <https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail> >>>> <#-1919795192_-2069969251_1162782367_-1582318301_DDB4FAA8-2DD7-40BB-A1B8-4E2AA1F9FDF2> >>>> >>>> 2016-01-16 0:18 GMT+01:00 Kai Wang <dep...@gmail.com>: >>>> >>>>> 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. >>>>>> >>>>> >>>>> >>>> >> >
