Re: Let PostgreSQL's On Schedule checkpoint write buffer smooth spread cycle by tuning IsCheckpointOnSchedule?
От | Fabien COELHO |
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Тема | Re: Let PostgreSQL's On Schedule checkpoint write buffer smooth spread cycle by tuning IsCheckpointOnSchedule? |
Дата | |
Msg-id | alpine.DEB.2.10.1512231515140.22350@sto обсуждение исходный текст |
Ответ на | Re: Let PostgreSQL's On Schedule checkpoint write buffer smooth spread cycle by tuning IsCheckpointOnSchedule? (Robert Haas <robertmhaas@gmail.com>) |
Ответы |
Re: Let PostgreSQL's On Schedule checkpoint write buffer
smooth spread cycle by tuning IsCheckpointOnSchedule?
|
Список | pgsql-hackers |
Hello Robert, >> I think that the 1.5 value somewhere in the patch is much too high for the >> purpose because it shifts the checkpoint load quite a lot (50% more load at >> the end of the checkpoint) just for the purpose of avoiding a spike which >> lasts a few seconds (I think) at the beginning. A much smaller value should >> be used (1.0 <= factor < 1.1), as it would be much less disruptive and would >> probably avoid the issue just the same. I recommend not to commit with a 1.5 >> factor in any case. > > Wait, what? On what workload does the FPW spike last only a few > seconds? [...] Ok. AFAICR, a relatively small part at the beginning of the checkpoint, but possibly more that a few seconds. My actual point is that it should be tested with different and especially smaller values, because 1.5 changes the overall load distribution *a lot*. For testing purpose I suggested that a guc would help, but the patch author has never been back to intervene on the thread, discuss the arguments not provide another patch. >> Another issue I raised is that the load change occurs both with xlog and >> time triggered checkpoints, and I'm sure it should be applied in both case. > > Is this sentence missing a "not"? Indeed. I think that it make sense for xlog triggered checkpoints, but less so with time triggered checkpoints. I may be wrong, but I think that this deserve careful analysis. -- Fabien.
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