Dear Eugen
Thank you for your input. What you say is true, of course. I've read
that some place too. I already ran a deep-scrub on all the involved PGs
and that's when the number of warnings increased drastically. I assume
that before I just had one positively huge omap object for that pool.
Now I have 167 omap objects that are not quite as big, but still too large.
Sincerely
Niklaus Hofer
On 19/06/2025 14.48, Eugen Block wrote:
Hi,
the warnings about large omap objects are reported when deep-scrubs
happen. So if you resharded the bucket (or Ceph did that for you),
you'll either have to wait for the deep-scrub schedule to scrub the
affected PGs, or you issue a manual deep-scrub on that PG or the entire
pool.
Regards,
Eugen
Zitat von Niklaus Hofer <niklaus.ho...@stepping-stone.ch>:
Dear all
We are running Ceph Pacific (16.2.15) with RadosGW and have been
getting "large omap objects" health warnings on the RadosGW index
pool. Indeed we had one bucket in particular that was positively huge
with 8'127'198 objects that had just a single shard. But we have been
seeing the message on some other buckets, too.
Eventually, we activated automatic resharding (rgw_dynamic_resharding
= true) and indeed this bucket was resharded to now 167 shards.
However, I am now getting even more large omap object warnings. On
that same bucket, too. The other buckets have not been resharded at
all. They are not in the queue, either:
| radosgw-admin reshard list
[]
| grep 'Large omap object found' /var/log/ceph/ceph* | grep 'PG: ' |
cut -d: -f 10 | cut -d. -f 4-5 | sort | uniq -c
2 7936686773.215
12 7937604172.149
10 7955243979.1209
9 7955243979.2480
13 7955243979.2481
12 7968198782.110
13 7968913553.67
11 7968913553.68
10 7968913553.69
11 7981210604.1
74 7981624399.1
217 7988881492.1
| radosgw-admin metadata list --metadata-key bucket.instance | grep -i
7988881492
"<bucket1_name>:<pool_name>.7988881492.1",
| radosgw-admin bucket stats --bucket <bucket1_name>
{
"bucket": "<bucket1_name>",
"num_shards": 167,
[...]
"usage": {
"rgw.main": {
"size": 9669928611955,
"size_actual": 9692804734976,
"size_utilized": 9669928611955,
"size_kb": 9443289661,
"size_kb_actual": 9465629624,
"size_kb_utilized": 9443289661,
"num_objects": 8134437
}
},
Let's check another one, too:
| radosgw-admin metadata list --metadata-key bucket.instance | grep -i
7968198782.110
"<bucket2_name>:<pool_name>.7968198782.110",
| radosgw-admin bucket stats --bucket <bucket2_name>
[...]
"num_objects": 38690
[...]
According to the documentation in [0], buckets are resharded at a
threshold of 100'000 objects per shard. For both of these, that
applies nicely, so it makes sense that they are not getting resharded
any further.
But why then am I getting these warnings?
Reading the documentation in [1], I can see that warnings are printed
at 200'000 entries per omap object. Can I assume that one object in an
RGW bucket means 1 entry in an omap object? Or is that a missconception?
Now, here is my working theory. Please let me know if that has any
merit or if I'm completely off:
The affected buckets have versioning activated. Plus object locking
too. They get used by a backup software (Kopia) that uses these
features to provide ransomware protection. So my thinking is that
maybe with versioning active, each object in a bucket could result in
multiple omap entries, maybe one per version or something?
If that is the case, then maybe I should reduce
`rgw_max_objs_per_shard` from 100'000 to something like 10'000 to have
the buckets resharded more aggressively?
But then again, that assumes a lot. For example, that assumes that the
num_objects counter in the bucket stats does not count up on versioned
objects. So my assumption could be completely whack.
What do you think? What can I do to get rid of the large omap objects?
Is more resharding going to help? What else could I check?
Sincerely
Niklaus Hofer
Links:
[0] https://docs.ceph.com/en/latest/radosgw/dynamicresharding/
#confval-rgw_max_objs_per_shard
[1] https://docs.ceph.com/en/latest/rados/operations/health-checks/
#large-omap-objects
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