Hi Zakhar, hello List, I just wanted to follow up on this and ask a few quesitions: Did you noticed any downsides with your compression settings so far? Do you have all mons now on compression? Did release updates go through without issues?Do you know if this works also with reef (we see massive writes as well there)?
Can you briefly tabulate the commands you used to persistently set the compression options?
Thanks so much, Dietmar On 10/18/23 06:14, Zakhar Kirpichenko wrote:
Many thanks for this, Eugen! I very much appreciate yours and Mykola's efforts and insight! Another thing I noticed was a reduction of RocksDB store after the reduction of the total PG number by 30%, from 590-600 MB: 65M 3675511.sst 65M 3675512.sst 65M 3675513.sst 65M 3675514.sst 65M 3675515.sst 65M 3675516.sst 65M 3675517.sst 65M 3675518.sst 62M 3675519.sst to about half of the original size: -rw-r--r-- 1 167 167 7218886 Oct 13 16:16 3056869.log -rw-r--r-- 1 167 167 67250650 Oct 13 16:15 3056871.sst -rw-r--r-- 1 167 167 67367527 Oct 13 16:15 3056872.sst -rw-r--r-- 1 167 167 63268486 Oct 13 16:15 3056873.sst Then when I restarted the monitors one by one before adding compression, RocksDB store reduced even further. I am not sure why and what exactly got automatically removed from the store: -rw-r--r-- 1 167 167 841960 Oct 18 03:31 018779.log -rw-r--r-- 1 167 167 67290532 Oct 18 03:31 018781.sst -rw-r--r-- 1 167 167 53287626 Oct 18 03:31 018782.sst Then I have enabled LZ4 and LZ4HC compression in our small production cluster (6 nodes, 96 OSDs) on 3 out of 5 monitors: compression=kLZ4Compression,bottommost_compression=kLZ4HCCompression. I specifically went for LZ4 and LZ4HC because of the balance between compression/decompression speed and impact on CPU usage. The compression doesn't seem to affect the cluster in any negative way, the 3 monitors with compression are operating normally. The effect of the compression on RocksDB store size and disk writes is quite noticeable: Compression disabled, 155 MB store.db, ~125 MB RocksDB sst, and ~530 MB writes over 5 minutes: -rw-r--r-- 1 167 167 4227337 Oct 18 03:58 3080868.log -rw-r--r-- 1 167 167 67253592 Oct 18 03:57 3080870.sst -rw-r--r-- 1 167 167 57783180 Oct 18 03:57 3080871.sst # du -hs /var/lib/ceph/3f50555a-ae2a-11eb-a2fc-ffde44714d86/mon.ceph04/store.db/; iotop -ao -bn 2 -d 300 2>&1 | grep ceph-mon 155M /var/lib/ceph/3f50555a-ae2a-11eb-a2fc-ffde44714d86/mon.ceph04/store.db/ 2471602 be/4 167 6.05 M 473.24 M 0.00 % 0.16 % ceph-mon -n mon.ceph04 -f --setuser ceph --setgroup ceph --default-log-to-file=false --default-log-to-stderr=true --default-log-stderr-prefix=debug --default-mon-cluster-log-to-file=false --default-mon-cluster-log-to-stderr=true [rocksdb:low0] 2471633 be/4 167 188.00 K 40.91 M 0.00 % 0.02 % ceph-mon -n mon.ceph04 -f --setuser ceph --setgroup ceph --default-log-to-file=false --default-log-to-stderr=true --default-log-stderr-prefix=debug --default-mon-cluster-log-to-file=false --default-mon-cluster-log-to-stderr=true [ms_dispatch] 2471603 be/4 167 16.00 K 24.16 M 0.00 % 0.01 % ceph-mon -n mon.ceph04 -f --setuser ceph --setgroup ceph --default-log-to-file=false --default-log-to-stderr=true --default-log-stderr-prefix=debug --default-mon-cluster-log-to-file=false --default-mon-cluster-log-to-stderr=true [rocksdb:high0] Compression enabled, 60 MB store.db, ~23 MB RocksDB sst, and ~130 MB of writes over 5 minutes: -rw-r--r-- 1 167 167 5766659 Oct 18 03:56 3723355.log -rw-r--r-- 1 167 167 22240390 Oct 18 03:56 3723357.sst # du -hs /var/lib/ceph/3f50555a-ae2a-11eb-a2fc-ffde44714d86/mon.ceph03/store.db/; iotop -ao -bn 2 -d 300 2>&1 | grep ceph-mon 60M /var/lib/ceph/3f50555a-ae2a-11eb-a2fc-ffde44714d86/mon.ceph03/store.db/ 2052031 be/4 167 1040.00 K 83.48 M 0.00 % 0.01 % ceph-mon -n mon.ceph03 -f --setuser ceph --setgroup ceph --default-log-to-file=false --default-log-to-stderr=true --default-log-stderr-prefix=debug --default-mon-cluster-log-to-file=false --default-mon-cluster-log-to-stderr=true [rocksdb:low0] 2052062 be/4 167 0.00 B 40.79 M 0.00 % 0.01 % ceph-mon -n mon.ceph03 -f --setuser ceph --setgroup ceph --default-log-to-file=false --default-log-to-stderr=true --default-log-stderr-prefix=debug --default-mon-cluster-log-to-file=false --default-mon-cluster-log-to-stderr=true [ms_dispatch] 2052032 be/4 167 16.00 K 4.68 M 0.00 % 0.00 % ceph-mon -n mon.ceph03 -f --setuser ceph --setgroup ceph --default-log-to-file=false --default-log-to-stderr=true --default-log-stderr-prefix=debug --default-mon-cluster-log-to-file=false --default-mon-cluster-log-to-stderr=true [rocksdb:high0] 2052052 be/4 167 44.00 K 0.00 B 0.00 % 0.00 % ceph-mon -n mon.ceph03 -f --setuser ceph --setgroup ceph --default-log-to-file=false --default-log-to-stderr=true --default-log-stderr-prefix=debug --default-mon-cluster-log-to-file=false --default-mon-cluster-log-to-stderr=true [msgr-worker-0] I haven't noticed a major CPU impact. Unfortunately I didn't specifically measure CPU time for monitors and , but overall the CPU impact of monitor store compression on our systems isn't noticeable. This may be different for larger clusters with larger RocksDB datasets, then perhaps compression=kLZ4Compression can be enabled by defualt and bottommost_compression=kLZ4HCCompression can be optional, in theory this should result in lower but much faster compression. I hope this helps. My plan is to keep the monitors with the current settings, i.e. 3 with compression + 2 without compression, until the next minor release of Pacific to see whether the monitors with compressed RocksDB store can be upgraded without issues. /Z On Tue, 17 Oct 2023 at 23:45, Eugen Block <eblock@xxxxxx> wrote:Hi Zakhar, I took a closer look into what the MONs really do (again with Mykola's help) and why manual compaction is triggered so frequently. With debug_paxos=20 I noticed that paxosservice and paxos triggered manual compactions. So I played with these values: paxos_service_trim_max = 1000 (default 500) paxos_service_trim_min = 500 (default 250) paxos_trim_max = 1000 (default 500) paxos_trim_min = 500 (default 250) This reduced the amount of writes by a factor of 3 or 4, the iotop values are fluctuating a bit, of course. As Mykola suggested I created a tracker issue [1] to increase the default values since they don't seem suitable for a production environment. Although I don't have tested that in production yet I'll ask one of our customers to do that in their secondary cluster (for rbd mirroring) where they also suffer from large mon stores and heavy writes to the mon store. Your findings with the compaction were quite helpful as well, we'll test that as well. Igor mentioned that the default bluestore_rocksdb config for OSDs will enable compression because of positive test results. If we can confirm that compression works well for MONs too, compression could be enabled by default as well. Regards, Eugen https://tracker.ceph.com/issues/63229 Zitat von Zakhar Kirpichenko <zakhar@xxxxxxxxx>:With the help of community members, I managed to enable RocksDBcompressionfor a test monitor, and it seems to be working well. Monitor w/o compression writes about 750 MB to disk in 5 minutes: 4854 be/4 167 4.97 M 755.02 M 0.00 % 0.24 % ceph-mon -n mon.ceph04 -f --setuser ceph --setgroup ceph --default-log-to-file=false --default-log-to-stderr=true --default-log-stderr-prefix=debug --default-mon-cluster-log-to-file=false --default-mon-cluster-log-to-stderr=true [rocksdb:low0] Monitor with LZ4 compression writes about 1/4 of that over the same time period: 2034728 be/4 167 172.00 K 199.27 M 0.00 % 0.06 % ceph-mon -n mon.ceph05 -f --setuser ceph --setgroup ceph --default-log-to-file=false --default-log-to-stderr=true --default-log-stderr-prefix=debug --default-mon-cluster-log-to-file=false --default-mon-cluster-log-to-stderr=true [rocksdb:low0] This is caused by the apparent difference in store.db sizes. Mon store.db w/o compression: # ls -al /var/lib/ceph/3f50555a-ae2a-11eb-a2fc-ffde44714d86/mon.ceph04/store.db total 257196 drwxr-xr-x 2 167 167 4096 Oct 16 14:00 . drwx------ 3 167 167 4096 Aug 31 05:22 .. -rw-r--r-- 1 167 167 1517623 Oct 16 14:00 3073035.log -rw-r--r-- 1 167 167 67285944 Oct 16 14:00 3073037.sst -rw-r--r-- 1 167 167 67402325 Oct 16 14:00 3073038.sst -rw-r--r-- 1 167 167 62364991 Oct 16 14:00 3073039.sst Mon store.db with compression: # ls -al /var/lib/ceph/3f50555a-ae2a-11eb-a2fc-ffde44714d86/mon.ceph05/store.db total 91188 drwxr-xr-x 2 167 167 4096 Oct 16 14:00 . drwx------ 3 167 167 4096 Oct 16 13:35 .. -rw-r--r-- 1 167 167 1760114 Oct 16 14:00 012693.log -rw-r--r-- 1 167 167 52236087 Oct 16 14:00 012695.sst There are no apparent downsides thus far. If everything works well, Iwilltry adding compression to other monitors. /Z On Mon, 16 Oct 2023 at 14:57, Zakhar Kirpichenko <zakhar@xxxxxxxxx>wrote:The issue persists, although to a lesser extent. Any comments from the Ceph team please? /Z On Fri, 13 Oct 2023 at 20:51, Zakhar Kirpichenko <zakhar@xxxxxxxxx>wrote:Some of it is transferable to RocksDB on mons nonetheless.Please point me to relevant Ceph documentation, i.e. a description ofhowvarious Ceph monitor and RocksDB tunables affect the operations of monitors, I'll gladly look into it.Please point me to such recommendations, if they're on docs.ceph.comI'llget them updated. This are the recommendations we used when we built our Pacific cluster: https://docs.ceph.com/en/pacific/start/hardware-recommendations/ Our drives are 4x times larger than recommended by this guide. Thedrivesare rated for < 0.5 DWPD, which is more than sufficient for bootdrives andstorage of rarely modified files. It is not documented or suggested anywhere that monitor processes write several hundred gigabytes ofdata perday, exceeding the amount of data written by OSDs. Which is why I amnotconvinced that what we're observing is expected behavior, but it's noteasyto get a definitive answer from the Ceph community. /Z On Fri, 13 Oct 2023 at 20:35, Anthony D'Atri <anthony.datri@xxxxxxxxx> wrote:Some of it is transferable to RocksDB on mons nonetheless. but their specs exceed Ceph hardware recommendations by a good margin Please point me to such recommendations, if they're on docs.ceph.comI'llget them updated. On Oct 13, 2023, at 13:34, Zakhar Kirpichenko <zakhar@xxxxxxxxx>wrote:Thank you, Anthony. As I explained to you earlier, the article you had sent is about RocksDB tuning for Bluestore OSDs, while the issue at hand is not with OSDs but rather monitors and their RocksDB store. Indeed, the drives are not enterprise-grade, but their specs exceed Ceph hardware recommendations by a good margin, they're being used as boot drivesonlyand aren't supposed to be written to continuously at high rates -which iswhat unfortunately is happening. I am trying to determine why it is happening and how the issue can be alleviated or resolved,unfortunatelymonitor RocksDB usage and tunables appear to be not documented at all. /Z On Fri, 13 Oct 2023 at 20:11, Anthony D'Atri <anthony.datri@xxxxxxxxxwrote:cf. Mark's article I sent you re RocksDB tuning. I suspect that with Reef you would experience fewer writes. Universal compaction mightalsohelp, but in the end this SSD is a client SKU and really not suitedforenterprise use. If you had the 1TB SKU you'd get much longer life, or you could change the overprovisioning on the ones you have. On Oct 13, 2023, at 12:30, Zakhar Kirpichenko <zakhar@xxxxxxxxx>wrote:I would very much appreciate it if someone with a betterunderstandingof monitor internals and use of RocksDB could please chip in._______________________________________________ ceph-users mailing list -- ceph-users@xxxxxxx To unsubscribe send an email to ceph-users-leave@xxxxxxx_______________________________________________ ceph-users mailing list -- ceph-users@xxxxxxx To unsubscribe send an email to ceph-users-leave@xxxxxxx_______________________________________________ ceph-users mailing list -- ceph-users@xxxxxxx To unsubscribe send an email to ceph-users-leave@xxxxxxx
-- _________________________________________________________ D i e t m a r R i e d e r Innsbruck Medical University Biocenter - Institute of Bioinformatics Innrain 80, 6020 Innsbruck Phone: +43 512 9003 71402 | Mobile: +43 676 8716 72402 Email: dietmar.rieder@xxxxxxxxxxx Web: http://www.icbi.at
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