On Wed, Mar 31, 2021 at 6:46 PM Patrick Donnelly <pdonnell@redhat.com> wrote:
>
> Hello Yongseok,
>
> On Wed, Mar 31, 2021 at 1:13 AM Yongseok Oh <yongseok.oh@linecorp.com> wrote:
> >
...
> > A few things I have analyzed
> > - Rejoining process consumes a considerable amount of time. That's a known issue. (Sometimes respawning MDS happened. Increasing mds_heartbeat_grace doesn't help.)
>
> Please turn up logging to:
>
> debug_mds = 5
>
> to get an idea what the MDS is doing when respawn occurs.
If it helps, here is a log with 2/5 from a recent failover which took
3.5 minutes: https://termbin.com/b022
This is 14.2.11 with the optimized recall/cache tuning.
the "Updating MDS map to version" keep showing from init-rejoin at around
2021-03-18 17:12:52.863
until
2021-03-18 17:22:36.356
while the rejoin itself finished at
2021-03-18 17:15:58.325
So,if it do associated to paxos(with too much changes between then), maybe pinning some
subtree/directory to particular mds/rank would help too.
Indeed rejoin is always the longest step -- even with cephfs_metadata
on SSDs. These MDSs had the cache limit set to 8GB, and you can see
that the rejoining MDS needed 56GB while booting.
I haven't had a chance to test the rejoin/openfiletables optimizations
yet. (https://github.com/ceph/ceph/pull/37383)
But I had understood that this is intended to decrease that rejoin
memory usage -- will it also speed things up?
-- dan
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