Hi,
Compaction can block reads, but on the write path you should be able to
absorb a certain amount of writes via the WAL before rocksdb starts
throttling writes. The larger and more WAL buffers you have, the more
writes you can absorb, but bigger buffers also take more CPU to keep in
sorted order and more aggregate buffer uses more RAM so it's a double
edged sword. I'd suggest looking and seeing how much time you actually
spend in compaction. For clusters that primarily are serving block via
RBD, there's a good chance it's actually fairly minimal. For RGW
(especially with lots of small objects and/or using erasure coding) you
might be spending more time in compaction, but it's important to see how
much.
FWIW, you can try running the following script against your OSD log to
see a summary of compaction events:
https://github.com/ceph/cbt/blob/master/tools/ceph_rocksdb_log_parser.py
Mark
On 11/15/21 10:48 AM, Szabo, Istvan (Agoda) wrote:
Hello,
If I’m not mistaken in my cluster this can block io on the osds if have a huge amount of objects on that specific osd.
How can I change the values to minimise the impact?
I guess it needs osd restart to make it effective and the “rocksdb options” are the values that needs to be tuned, but what should it be changed?
Istvan Szabo
Senior Infrastructure Engineer
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Agoda Services Co., Ltd.
e: istvan.szabo@xxxxxxxxx<mailto:istvan.szabo@xxxxxxxxx>
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