[ceph-users] CephFS - large omap object

Dylan McCulloch dmc at unimelb.edu.au
Mon Mar 18 03:05:11 PDT 2019


>
>cephfs does not create/use object "4.00000000".  Please show us some
>of its keys.
>

https://pastebin.com/WLfLTgni
Thanks

>On Mon, Mar 18, 2019 at 4:16 PM Dylan McCulloch <dmc at unimelb.edu.au> wrote:
>>
>> Hi all,
>>
>> We have a large omap object warning on one of our Ceph clusters.
>> The only reports I've seen regarding the "large omap objects" warning from other users were related to RGW bucket sharding, however we do not have RGW configured on this cluster.
>> The large omap object ~10GB resides in a CephFS metadata pool.
>>
>> It's perhaps worth mentioning that we had to perform disaster recovery steps [1] on this cluster last year after a network issue, so we're not sure whether this large omap object is a result of those previous recovery processes or whether it's completely unrelated.
>>
>> Ceph version: 12.2.8
>> osd_objectstore: Bluestore
>> RHEL 7.5
>> Kernel: 4.4.135-1.el7.elrepo.x86_64
>>
>> We have set: "mds_bal_fragment_size_max": "500000" (Default 100000)
>>
>> $ ceph health detail
>> HEALTH_WARN 1 large omap objects
>> LARGE_OMAP_OBJECTS 1 large omap objects
>>     1 large objects found in pool 'hpcfs_metadata'
>>     Search the cluster log for 'Large omap object found' for more details.
>>
>> # Find pg with large omap object
>> $ for i in `ceph pg ls-by-pool hpcfs_metadata | tail -n +2 | awk '{print $1}'`; do echo -n "$i: "; ceph pg $i query |grep num_large_omap_objects | head -1 | awk '{print $2}'; done | grep ": 1"
>> 20.103: 1
>>
>> # OSD log entry showing relevant object
>> osd.143 osd.143 172.26.74.23:6826/3428317 1380 : cluster [WRN] Large omap object found. Object: 20:c0ce80d4:::4.00000000:head Key count: 24698995 Size (bytes): 11410935690
>>
>> # Confirm default warning thresholds for large omap object
>> $ ceph daemon osd.143 config show | grep osd_deep_scrub_large_omap
>>     "osd_deep_scrub_large_omap_object_key_threshold": "2000000",
>>     "osd_deep_scrub_large_omap_object_value_sum_threshold": "1073741824",
>>
>> # Dump keys/values of problematic object, creates 46.65GB file
>> $ rados -p hpcfs_metadata listomapvals '4.00000000' > /tmp/hpcfs_metadata_object_omap_vals_4.00000000_20190304
>> $ ll /tmp/hpcfs_metadata_object_omap_vals_4.00000000_20190304
>> -rw-r--r-- 1 root root 50089561860 Mar  4 18:16 /tmp/hpcfs_metadata_object_omap_vals_4.00000000_20190304
>>
>> # Confirm key count matches OSD log entry warning
>> $ rados -p hpcfs_metadata listomapkeys '4.00000000' | wc -l
>> 24698995
>>
>> # The omap keys/vals for that object appear to have been unchanged/static for at least a couple of months:
>> $ sha1sum /tmp/hpcfs_metadata_object_omap_vals_4.00000000_20190304
>> fd00ceb68607b477626178b2d81fefb926460107  /tmp/hpcfs_metadata_object_omap_vals_4.00000000_20190304
>> $ sha1sum /tmp/hpcfs_metadata_object_omap_vals_4_00000000_20190108
>> fd00ceb68607b477626178b2d81fefb926460107  /tmp/hpcfs_metadata_object_omap_vals_4_00000000_20190108
>>
>> I haven't gone through all 24698995 keys yet, but while most appear to relate to objects in the hpcfs_data CephFS data pool, there are a significant number of keys (rough guess 25%) that don't appear to have corresponding objects in the hpcfs_data pool.
>>
>> Any assistance or pointers to troubleshoot further would be very much appreciated.
>>
>> Thanks,
>> Dylan
>>
>> [1] http://docs.ceph.com/docs/luminous/cephfs/disaster-recovery/
>>
>> _______________________________________________
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>> ceph-users at lists.ceph.com
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>

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