Hello, I thought I'd post an update. Setting the pg_log size to 500, and running the offline trim operation sequentially on all OSDs seems to help. With our current setup, it takes about 12-48h per node, depending on the pgs per osd. The PG amounts per OSD we have are ~180-750, with a majority around 200, and some nodes consistently have 500 per OSD. The limiting factor of the recovery time seems to be our nvme, which we use for rocksdb for the OSDs.
We haven't fully recovered yet, we're working on it. Almost all our PGs are back up, we still have ~40/18000 PGs down, but I think we'll get there. Currently ~40 OSDs/1200 down. It seems like the previous mention of 32kB / pg_log entry seems in the correct magnitude for us too. If we count 32kB * 200 pgs * 3000 log entries, we're close to the 20 GB / OSD process. For the nodes that have been trimmed, we're hovering around 100 GB/node of memory use, or ~4 GB per OSD, and so far seems stable, but we don't have longer term data on that, and we don't know exactly how it behaves when load is applied. However if we're currently at the pg_log limit of 500, adding load should hopefully not increase pg_log memory consumption. Cheers, Kalle ----- Original Message ----- > From: "Kalle Happonen" <kalle.happo...@csc.fi> > To: "Dan van der Ster" <d...@vanderster.com> > Cc: "ceph-users" <ceph-users@ceph.io> > Sent: Tuesday, 17 November, 2020 16:07:03 > Subject: [ceph-users] Re: osd_pglog memory hoarding - another case > Hi, > >> I don't think the default osd_min_pg_log_entries has changed recently. >> In https://tracker.ceph.com/issues/47775 I proposed that we limit the >> pg log length by memory -- if it is indeed possible for log entries to >> get into several MB, then this would be necessary IMHO. > > I've had a surprising crash course on pg_log in the last 36 hours. But for the > size of each entry, you're right. I counted pg log * ODS, and did not take > into > factor pg log * OSDs * pgs on the OSD. Still the total memory use that an OSD > uses for pg_log was ~22GB / OSD process. > > >> But you said you were trimming PG logs with the offline tool? How long >> were those logs that needed to be trimmed? > > The logs we are trimming were ~3000, we trimmed them to the new size of 500. > After restarting the OSDs, it dropped the pg_log memory usage from ~22GB, to > what we guess is 2-3GB but with the cluster at this state, it's hard to be > specific. > > Cheers, > Kalle > > > >> -- dan >> >> >> On Tue, Nov 17, 2020 at 11:58 AM Kalle Happonen <kalle.happo...@csc.fi> >> wrote: >>> >>> Another idea, which I don't know if has any merit. >>> >>> If 8 MB is a realistic log size (or has this grown for some reason?), did >>> the >>> enforcement (or default) of the minimum value change lately >>> (osd_min_pg_log_entries)? >>> >>> If the minimum amount would be set to 1000, at 8 MB per log, we would have >>> issues with memory. >>> >>> Cheers, >>> Kalle >>> >>> >>> >>> ----- Original Message ----- >>> > From: "Kalle Happonen" <kalle.happo...@csc.fi> >>> > To: "Dan van der Ster" <d...@vanderster.com> >>> > Cc: "ceph-users" <ceph-users@ceph.io> >>> > Sent: Tuesday, 17 November, 2020 12:45:25 >>> > Subject: [ceph-users] Re: osd_pglog memory hoarding - another case >>> >>> > Hi Dan @ co., >>> > Thanks for the support (moral and technical). >>> > >>> > That sounds like a good guess, but it seems like there is nothing >>> > alarming here. >>> > In all our pools, some pgs are a bit over 3100, but not at any exceptional >>> > values. >>> > >>> > cat pgdumpfull.txt | jq '.pg_map.pg_stats[] | >>> > select(.ondisk_log_size > 3100)' | egrep "pgid|ondisk_log_size" >>> > "pgid": "37.2b9", >>> > "ondisk_log_size": 3103, >>> > "pgid": "33.e", >>> > "ondisk_log_size": 3229, >>> > "pgid": "7.2", >>> > "ondisk_log_size": 3111, >>> > "pgid": "26.4", >>> > "ondisk_log_size": 3185, >>> > "pgid": "33.4", >>> > "ondisk_log_size": 3311, >>> > "pgid": "33.8", >>> > "ondisk_log_size": 3278, >>> > >>> > I also have no idea what the average size of a pg log entry should be, in >>> > our >>> > case it seems it's around 8 MB (22GB/3000 entires). >>> > >>> > Cheers, >>> > Kalle >>> > >>> > ----- Original Message ----- >>> >> From: "Dan van der Ster" <d...@vanderster.com> >>> >> To: "Kalle Happonen" <kalle.happo...@csc.fi> >>> >> Cc: "ceph-users" <ceph-users@ceph.io>, "xie xingguo" >>> >> <xie.xing...@zte.com.cn>, >>> >> "Samuel Just" <sj...@redhat.com> >>> >> Sent: Tuesday, 17 November, 2020 12:22:28 >>> >> Subject: Re: [ceph-users] osd_pglog memory hoarding - another case >>> > >>> >> Hi Kalle, >>> >> >>> >> Do you have active PGs now with huge pglogs? >>> >> You can do something like this to find them: >>> >> >>> >> ceph pg dump -f json | jq '.pg_map.pg_stats[] | >>> >> select(.ondisk_log_size > 3000)' >>> >> >>> >> If you find some, could you increase to debug_osd = 10 then share the >>> >> osd log. >>> >> I am interested in the debug lines from calc_trim_to_aggressively (or >>> >> calc_trim_to if you didn't enable pglog_hardlimit), but the whole log >>> >> might show other issues. >>> >> >>> >> Cheers, dan >>> >> >>> >> >>> >> On Tue, Nov 17, 2020 at 9:55 AM Dan van der Ster <d...@vanderster.com> >>> >> wrote: >>> >>> >>> >>> Hi Kalle, >>> >>> >>> >>> Strangely and luckily, in our case the memory explosion didn't reoccur >>> >>> after that incident. So I can mostly only offer moral support. >>> >>> >>> >>> But if this bug indeed appeared between 14.2.8 and 14.2.13, then I >>> >>> think this is suspicious: >>> >>> >>> >>> b670715eb4 osd/PeeringState: do not trim pg log past >>> >>> last_update_ondisk >>> >>> >>> >>> https://github.com/ceph/ceph/commit/b670715eb4 >>> >>> >>> >>> Given that it adds a case where the pg_log is not trimmed, I wonder if >>> >>> there could be an unforeseen condition where `last_update_ondisk` >>> >>> isn't being updated correctly, and therefore the osd stops trimming >>> >>> the pg_log altogether. >>> >>> >>> >>> Xie or Samuel: does that sound possible? >>> >>> >>> >>> Cheers, Dan >>> >>> >>> >>> On Tue, Nov 17, 2020 at 9:35 AM Kalle Happonen <kalle.happo...@csc.fi> >>> >>> wrote: >>> >>> > >>> >>> > Hello all, >>> >>> > wrt: >>> >>> > https://lists.ceph.io/hyperkitty/list/ceph-users@ceph.io/thread/7IMIWCKIHXNULEBHVUIXQQGYUDJAO2SF/ >>> >>> > >>> >>> > Yesterday we hit a problem with osd_pglog memory, similar to the >>> >>> > thread above. >>> >>> > >>> >>> > We have a 56 node object storage (S3+SWIFT) cluster with 25 OSD disk >>> >>> > per node. >>> >>> > We run 8+3 EC for the data pool (metadata is on replicated nvme pool). >>> >>> > >>> >>> > The cluster has been running fine, and (as relevant to the post) the >>> >>> > memory >>> >>> > usage has been stable at 100 GB / node. We've had the default pg_log >>> >>> > of 3000. >>> >>> > The user traffic doesn't seem to have been exceptional lately. >>> >>> > >>> >>> > Last Thursday we updated the OSDs from 14.2.8 -> 14.2.13. On Friday >>> >>> > the memory >>> >>> > usage on OSD nodes started to grow. On each node it grew steadily >>> >>> > about 30 >>> >>> > GB/day, until the servers started OOM killing OSD processes. >>> >>> > >>> >>> > After a lot of debugging we found that the pg_logs were huge. Each >>> >>> > OSD process >>> >>> > pg_log had grown to ~22GB, which we naturally didn't have memory for, >>> >>> > and then >>> >>> > the cluster was in an unstable situation. This is significantly more >>> >>> > than the >>> >>> > 1,5 GB in the post above. We do have ~20k pgs, which may directly >>> >>> > affect the >>> >>> > size. >>> >>> > >>> >>> > We've reduced the pg_log to 500, and started offline trimming it >>> >>> > where we can, >>> >>> > and also just waited. The pg_log size dropped to ~1,2 GB on at least >>> >>> > some >>> >>> > nodes, but we're still recovering, and have a lot of ODSs down and >>> >>> > out still. >>> >>> > >>> >>> > We're unsure if version 14.2.13 triggered this, or if the osd >>> >>> > restarts triggered >>> >>> > this (or something unrelated we don't see). >>> >>> > >>> >>> > This mail is mostly to figure out if there are good guesses why the >>> >>> > pg_log size >>> >>> > per OSD process exploded? Any technical (and moral) support is >>> >>> > appreciated. >>> >>> > Also, currently we're not sure if 14.2.13 triggered this, so this is >>> >>> > also to >>> >>> > put a data point out there for other debuggers. >>> >>> > >>> >>> > Cheers, >>> >>> > Kalle Happonen >>> >>> > _______________________________________________ >>> >>> > ceph-users mailing list -- ceph-users@ceph.io >>> >> > > To unsubscribe send an email to ceph-users-le...@ceph.io >>> > _______________________________________________ >>> > ceph-users mailing list -- ceph-users@ceph.io >> > > To unsubscribe send an email to ceph-users-le...@ceph.io > _______________________________________________ > ceph-users mailing list -- ceph-users@ceph.io > To unsubscribe send an email to ceph-users-le...@ceph.io _______________________________________________ ceph-users mailing list -- ceph-users@ceph.io To unsubscribe send an email to ceph-users-le...@ceph.io
