Hey Igor,
On 07/07/2021 14:59, Igor Fedotov wrote:
after an upgrade from Ceph Nautilus to Octopus we ran into extreme
performance issues leading to an unusable cluster
when doing a larger snapshot delete and the cluster doing snaptrims,
see i.e. https://tracker.ceph.com/issues/50511#note-13.
Since this was not an issue prior to the upgrade, maybe the
conversion of the OSD to OMAP caused this degradation of the RocksDB
data structures, maybe not. (We were running bluefs_buffered_io=true,
so that was NOT the issue here).
It's hard to say what exactly caused the issue this time. Indeed OMAP
conversion could have some impact since it had performed bulk removal
along the upgrade process - so DB could gain critical mass to start
lagging.
But I presume this is a one-time effect - it should vaporize after DB
compaction. Which doesn't mean that snaptrims or any other bulk
removals are absolutely safe since then though.
Thank you very much for your quick and extensive reply!
If OMAP conversion could have this effect, maybe it's sensible to
trigger either an an immediate online compaction to the end of the
conversion or at least add this to the upgrade notes. I suppose with the
EoL of Nautilus more and more clusters will now make the jump to the
Octopus release and convert their OSDs to OMAP in the process. Even if
not all clusters RocksDBs would go over the edge, in any case running a
compaction should not hurt right?
Thanks again,
Christian
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