1 Large omap object found - ceph-users

31 Jul 2023

I've been going round and round in circles trying to work this one out but I'm
getting nowhere.  We're running a 4 node quincy cluster (17.2.6) which recently
reported the following:

ceph.log-20230729.gz:2023-07-28T08:31:42.390003+0000 osd.26 (osd.26) 13834 : cluster [WRN]
Large omap object found. Object:
5:6c65dd84:users.uid::callrecordings$callrecordings_rw.buckets:head PG: 5.21bba636 (5.16)
Key count: 378454 Size (bytes): 75565579

This happened a week or so ago (only the key count was only just over the 200000 threshold
on that occasion) and after much searching around, I found an article that suggested a
deep scrub on the pg would likely resolve the issue, so I forced a deep scrub and shortly
after, the warning cleared.  Came into the office today to discover the above.  It's
on the same PG as before which is in the default.rgw.meta pool.  This time, after forcing
a deep-scrub on that PG, nothing changed.  I did it a second time just to be sure but got
the same result.

I keep finding a suse article that simply suggests increasing the threshold to the
previous default of 2,000,000, but other articles I read say it was lowered for a reason
and that by the time it hits that figure, it's too late so I don't want to just
mask it.  Problem is that I don't really understand it.   I found a thread here from a
bit over two years ago but their issue was in the default.rgw.buckets.index pool.  A step
in the solution was to list out the problematic object id and check the objects per shard
however, if I issue the command "rados -p default.rgw.meta ls" it returns
nothing.  I get a big list from "rados -p default.rgw.buckets.index ls" just
nothing from the first pool.  I think it may be because the meta pool isn't indexed
based on something I read, but I really don't know what I'm talking about tbh.

I don't know if this is helpful, but if I list out all the PGs for that pool, there
are 32 PGs and 5.16 shows 80186950 bytes and 401505 keys.  PG 5.c has 75298 and 384 keys. 
The remaining 30 PGs show zero bytes and zero keys.  I'm really not sure how to
troubleshoot and resolve from here.  For the record, dynamic resharding is enabled in that
no options have been set in the config and that is the default setting.

Based on the suse article I mentioned which also references the default.rgw.meta pool,
I'm gathering our issue is because we have so many buckets that are all owned by the
one user and the solution is either:

* delete unused buckets
* create multiple users and spread buckets evenly across all users (not something we can
do)
* increase the threshold to stop the warning

Problem is that I'm having trouble verifying this is the issue.  I've tried
dumping out bucket stats to a file (radosgw-admin bucket stats > bucket_stats.txt) but
after three hours this is still running with no output.

Thanks for your time,
Mark