17 Nov
2020
17 Nov
'20
11:55 a.m.
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.happonen(a)csc.fi> wrote:
>
> Hello all,
> wrt:
https://lists.ceph.io/hyperkitty/list/ceph-users@ceph.io/thread/7IMIWCKIHXN…
>
> 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
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