[ceph-users] Resolving Large omap objects in RGW index pool

Chris Sarginson csargiso at gmail.com
Thu Oct 4 07:22:59 PDT 2018


Ceph version: Luminous 12.2.7

Following upgrading to Luminous from Jewel we have been stuck with a
cluster in HEALTH_WARN state that is complaining about large omap objects.
These all seem to be located in our .rgw.buckets.index pool.  We've
disabled auto resharding on bucket indexes due to seeming looping issues
after our upgrade.  We've reduced the number reported of reported large
omap objects by initially increasing the following value:

~# ceph daemon mon.ceph-mon-1 config get
    "osd_deep_scrub_large_omap_object_value_sum_threshold": "2147483648"

However we're still getting a warning about a single large OMAP object,
however I don't believe this is related to an unsharded index - here's the
log entry:

2018-10-01 13:46:24.427213 osd.477 osd.477 8482 :
cluster [WRN] Large omap object found. Object:
15:333d5ad7:::.dir.default.5689810.107:head Key count: 17467251 Size
(bytes): 4458647149

The object in the logs is the "marker" object, rather than the bucket_id -
I've put some details regarding the bucket here:


The bucket limit check shows that the index is sharded, so I think this
might be related to versioning, although I was unable to get confirmation
that the bucket in question has versioning enabled through the aws
cli(snipped debug output below)

2018-10-02 15:11:17,530 - MainThread - botocore.parsers - DEBUG - Response
headers: {'date': 'Tue, 02 Oct 2018 14:11:17 GMT', 'content-length': '137',
'x-amz-request-id': 'tx0000000000000020e3b15-005bb37c85-15870fe0-default',
'content-type': 'application/xml'}
2018-10-02 15:11:17,530 - MainThread - botocore.parsers - DEBUG - Response
<?xml version="1.0" encoding="UTF-8"?><VersioningConfiguration xmlns="

After dumping the contents of large omap object mentioned above into a file
it does seem to be a simple listing of the bucket contents, potentially an
old index:

~# wc -l omap_keys
17467251 omap_keys

This is approximately 5 million below the currently reported number of
objects in the bucket.

When running the commands listed here:

The problematic bucket is listed in the output (along with 72 other
"CLIENTBUCKET", "default.294495648.690", "default.5689810.107"

As this tests for bucket_id and marker fields not matching to print out the
information, is the implication here that both of these should match in
order to fully migrate to the new sharded index?

I was able to do a "metadata get" using what appears to be the old index
object ID, which seems to support this (there's a "new_bucket_instance_id"
field, containing a newer "bucket_id" and reshard_status is 2, which seems
to suggest it has completed).

I am able to take the "new_bucket_instance_id" and get additional metadata
about the bucket, each time I do this I get a slightly newer
"new_bucket_instance_id", until it stops suggesting updated indexes.

It's probably worth pointing out that when going through this process the
final "bucket_id" doesn't match the one that I currently get when running
'radosgw-admin bucket stats --bucket "CLIENTBUCKET"', even though it also
suggests that no further resharding has been done as "reshard_status" = 0
and "new_bucket_instance_id" is blank.  The output is available to view


It would be useful if anyone can offer some clarification on how to proceed
from this situation, identifying and removing any old/stale indexes from
the index pool (if that is the case), as I've not been able to spot
anything in the archives.

If there's any further information that is needed for additional context
please let me know.

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