Hi,

last week we had a "large omap" warning in one of our clusters. The
affected object was

025-11-09T23:31:24.799+0000 7f70131b3640  0 log_channel(cluster) log
[WRN] : Large omap object found. Object:
2:ddb71591:::mds1_openfiles.d:head PG: 2.89a8edbb (2.b) Key count:
200001 Size (bytes): 12122520

I wanted to get a deeper understanding on what triggers this specific issue
and had a look at the code - I'm not that deep into C++, so please, correct
me if I'm wrong.

If I understand correctly, LARGE_OMAP warnings are only generated (and
cleared) during deep-scrubs. If an object is found with more keys
than osd_deep_scrub_large_omap_object_key_threshold, it will trigger the
warning. In this case

mds1_openfiles.d had a Key count of 200001 while this specific option
got deep-scrubbed and that triggered the warning

The MDS should create a new openfiles fragment when the threshold is reached.

My question is: How exactly does the MDS end up with an openfiles
segment with more than 200000? Shouldn't the MDS create a new segment
as soon as the previous one reaches the configured limit?

If this is considered a bug, I'm happy to open a report.


Best regards

Philipp

-- 

Philipp Hocke
Leiter Linux Systemadministration / Head Of TechOps
CM4ALL GmbH
Im Mediapark 6A - 50670 Köln / Cologne
Phone +49-(0)221-6601-0 <https://outlook.office.com/mail/sentitems>
Fax +49-(0)221-6601-1011 <https://outlook.office.com/mail/sentitems>
E-Mail: [email protected]
Internet: www.cm4all.com
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