Jay, await, according to iostat's man page it is the time of a request to the disk to get served. You may try changing the io scheduler. I've read that noop it's recommended for SSDs, you can check here http://goo.gl/XMiIA
Regarding compaction, a week ago we had serious problems with compaction in a test machine, solved by changing from openjdk 1.6 to sun-jdk 1.6. On Thu, Apr 18, 2013 at 2:08 PM, Jay Svc <jaytechg...@gmail.com> wrote: > By the way the compaction and commit log disk latency, these are two > seperate problems I see. > > The important one is compaction problem, How I can speed that up? > > Thanks, > Jay > > > On Thu, Apr 18, 2013 at 12:07 PM, Jay Svc <jaytechg...@gmail.com> wrote: > >> Looks like formatting is bit messed up. Please let me know if you want >> the same in clean format. >> >> Thanks, >> Jay >> >> >> On Thu, Apr 18, 2013 at 12:05 PM, Jay Svc <jaytechg...@gmail.com> wrote: >> >>> Hi Aaron, Alexis, >>> >>> Thanks for reply, Please find some more details below. >>> >>> *Core problems:* Compaction is taking longer time to finish. So it will >>> affect my reads. I have more CPU and memory, want to utilize that to speed >>> up the compaction process. >>> *Parameters used:* >>> >>> 1. SSTable size: 500MB (tried various sizes from 20MB to 1GB) >>> 2. Compaction throughput mb per sec: 250MB (tried from 16MB to 640MB) >>> 3. Concurrent write: 196 (tried from 32 to 296) >>> 4. Concurrent compactors: 72 (tried disabling to making it 172) >>> 5. Multithreaded compaction: true (tried both true and false) >>> 6. Compaction strategy: LCS (tried STCS as well) >>> 7. Memtable total space in mb: 4096 MB (tried default and some other >>> params too) >>> >>> Note: I have tried almost all permutation combination of these >>> parameters. >>> *Observations: * >>> I ran test for 1.15 hrs with writes at the rate of 21000 >>> records/sec(total 60GB data during 1.15 hrs). After I stopped the test >>> compaction took additional 1.30 hrs to finish compaction, that reduced >>> the SSTable count from 170 to 17. >>> CPU(24 cores): almost 80% idle during the run >>> JVM: 48G RAM, 8G Heap, (3G to 5G heap used) >>> Pending Writes: sometimes high spikes for small amount of time otherwise >>> pretty flat >>> Aaron, Please find the iostat below: the sdb and dm-2 are the >>> commitlog disks. >>> Please find the iostat of some of 3 different boxes in my cluster. >>> -bash-4.1$ iostat -xkcd >>> Linux 2.6.32-358.2.1.el6.x86_64 (edc-epod014-dl380-3) 04/18/2013 >>> _x86_64_ (24 CPU) >>> avg-cpu: %user %nice %system %iowait %steal %idle >>> 1.20 1.11 0.59 0.01 0.00 97.09 >>> Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s avgrq-sz avgqu-sz awaitsvctm >>> %util >>> sda 0.03 416.56 9.00 7.08 1142.49 1694.55 352.88 0.07 4.08 0.57 0.92 >>> sdb 0.00 172.38 0.08 3.34 10.76 702.89 416.96 0.09 24.84 0.94 >>> 0.32<24.84%C2%A0%C2%A0%200.94%C2%A0%C2%A0%200.32> >>> dm-0 0.00 0.00 0.03 0.75 0.62 3.00 9.24 0.00 1.45 0.33 0.03 >>> dm-1 0.00 0.00 0.00 0.00 0.00 0.00 8.00 0.00 0.74 0.68 0.00 >>> dm-2 0.00 0.00 0.08 175.72 10.76 702.89 8.12 3.26 18.49 0.02 0.32 >>> dm-3 0.00 0.00 0.00 0.00 0.00 0.00 7.97 0.00 0.83 0.62 0.00 >>> dm-4 0.00 0.00 8.99 422.89 1141.87 1691.55 13.12 4.64 10.71 0.02 0.90 >>> -bash-4.1$ iostat -xkcd >>> Linux 2.6.32-358.2.1.el6.x86_64 (ndc-epod014-dl380-1) 04/18/2013 >>> _x86_64_ (24 CPU) >>> avg-cpu: %user %nice %system %iowait %steal %idle >>> 1.20 1.12 0.52 0.01 0.00 97.14 >>> Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s avgrq-sz avgqu-sz await svc >>> sda 0.01 421.17 9.22 7.43 1167.81 1714.38 346.10 0.07 3.99 0. >>> sdb 0.00 172.68 0.08 3.26 10.52 703.74 427.79 0.08 25.01 0. >>> dm-0 0.00 0.00 0.04 1.04 0.89 4.16 9.34 0.00 2.58 0. >>> dm-1 0.00 0.00 0.00 0.00 0.00 0.00 8.00 0.00 0.77 0. >>> dm-2 0.00 0.00 0.08 175.93 10.52 703.74 8.12 3.13 17.78 0. >>> dm-3 0.00 0.00 0.00 0.00 0.00 0.00 7.97 0.00 1.14 0. >>> dm-4 0.00 0.00 9.19 427.55 1166.91 1710.21 13.18 4.67 10.65 0. >>> -bash-4.1$ iostat -xkcd >>> Linux 2.6.32-358.2.1.el6.x86_64 (edc-epod014-dl380-1) 04/18/2013 >>> _x86_64_ (24 CPU) >>> avg-cpu: %user %nice %system %iowait %steal %idle >>> 1.15 1.13 0.52 0.01 0.00 97.19 >>> Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s avgrq-sz avgqu-sz await svctm >>> %util >>> sda 0.02 429.97 9.28 7.29 1176.81 1749.00 353.12 0.07 4.10 0.55 0.91 >>> sdb 0.00 173.65 0.08 3.09 10.50 706.96 452.25 0.09 27.23 0.99 0.31 >>> dm-0 0.00 0.00 0.04 0.79 0.82 3.16 9.61 0.00 1.54 0.27 0.02 >>> dm-1 0.00 0.00 0.00 0.00 0.00 0.00 8.00 0.00 0.68 0.63 0.00 >>> dm-2 0.00 0.00 0.08 176.74 10.50 706.96 8.12 3.46 19.53 0.02 0.31 >>> dm-3 0.00 0.00 0.00 0.00 0.00 0.00 7.97 0.00 0.85 0.83 0.00 >>> dm-4 0.00 0.00 9.26 436.46 1175.98 1745.84 13.11 0.03 0.03 0.02 0.89 >>> Thanks, >>> Jay >>> >>> >>> On Thu, Apr 18, 2013 at 2:50 AM, aaron morton >>> <aa...@thelastpickle.com>wrote: >>> >>>> > I believe that compaction occurs on the data directories and not in >>>> the commitlog. >>>> Yes, compaction only works on the data files. >>>> >>>> > When I ran iostat; I see "await" 26ms to 30 ms for my commit log >>>> disk. My CPU is less than 18% used. >>>> > >>>> > How I reduce the disk latency for my commit log disk. They are SSDs. >>>> That does not sound right. Can you include the output from iostat for >>>> the commit log and data volumes. Also some information on how many writes >>>> you are processing the the size of rows as well. >>>> >>>> Cheers >>>> >>>> ----------------- >>>> Aaron Morton >>>> Freelance Cassandra Consultant >>>> New Zealand >>>> >>>> @aaronmorton >>>> http://www.thelastpickle.com >>>> >>>> On 18/04/2013, at 11:58 AM, Alexis Rodríguez < >>>> arodrig...@inconcertcc.com> wrote: >>>> >>>> > Jay, >>>> > >>>> > I believe that compaction occurs on the data directories and not in >>>> the commitlog. >>>> > >>>> > http://wiki.apache.org/cassandra/MemtableSSTable >>>> > >>>> > >>>> > >>>> > >>>> > On Wed, Apr 17, 2013 at 7:58 PM, Jay Svc <jaytechg...@gmail.com> >>>> wrote: >>>> > Hi Alexis, >>>> > >>>> > Thank you for your response. >>>> > >>>> > My commit log is on SSD. which shows me 30 to 40 ms of disk latency. >>>> > >>>> > When I ran iostat; I see "await" 26ms to 30 ms for my commit log >>>> disk. My CPU is less than 18% used. >>>> > >>>> > How I reduce the disk latency for my commit log disk. They are SSDs. >>>> > >>>> > Thank you in advance, >>>> > Jay >>>> > >>>> > >>>> > On Wed, Apr 17, 2013 at 3:58 PM, Alexis Rodríguez < >>>> arodrig...@inconcertcc.com> wrote: >>>> > :D >>>> > >>>> > Jay, check if your disk(s) utilization allows you to change the >>>> configuration the way Edward suggest. iostat -xkcd 1 will show you how much >>>> of your disk(s) are in use. >>>> > >>>> > >>>> > >>>> > >>>> > On Wed, Apr 17, 2013 at 5:26 PM, Edward Capriolo < >>>> edlinuxg...@gmail.com> wrote: >>>> > three things: >>>> > 1) compaction throughput is fairly low (yaml nodetool) >>>> > 2) concurrent compactions is fairly low (yaml) >>>> > 3) multithreaded compaction might be off in your version >>>> > >>>> > Try raising these things. Otherwise consider option 4. >>>> > >>>> > 4)$$$$$$$$$$$$$$$$$$$$$$$ RAID,RAM<CPU$$$$$$$$$$$$$$ >>>> > >>>> > >>>> > On Wed, Apr 17, 2013 at 4:01 PM, Jay Svc <jaytechg...@gmail.com> >>>> wrote: >>>> > Hi Team, >>>> > >>>> > >>>> > I have a high write traffic to my Cassandra cluster. I experience a >>>> very high number of pending compactions. As I expect higher writes, The >>>> pending compactions keep increasing. Even when I stop my writes it takes >>>> several hours to finishing pending compactions. >>>> > >>>> > My CF is configured with LCS, with sstable_size_mb=20M. My CPU is >>>> below 20%, JVM memory usage is between 45%-55%. I am using Cassandra 1.1.9. >>>> > >>>> > How can I increase the compaction rate so it will run bit faster to >>>> match my write speed? >>>> > >>>> > Your inputs are appreciated. >>>> > >>>> > Thanks, >>>> > Jay >>>> > >>>> > >>>> > >>>> > >>>> > >>>> >>>> >>> >> >
