Re: any impact to DML sql statements when checkpoint starting

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От David G. Johnston
Тема Re: any impact to DML sql statements when checkpoint starting
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Msg-id CAKFQuwad6xiKpVs0NiSHMD71eivTUXRchJFhOH0ZHrfM36M2yg@mail.gmail.com
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Ответ на RE: any impact to DML sql statements when checkpoint starting  ("James Pang (chaolpan)" <chaolpan@cisco.com>)
Ответы RE: any impact to DML sql statements when checkpoint starting  ("James Pang (chaolpan)" <chaolpan@cisco.com>)
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On Thu, Feb 3, 2022 at 5:45 PM James Pang (chaolpan) <chaolpan@cisco.com> wrote:

So the main concern about checkpoint impact  is IO,  in order to reduce the IO by checkpoint, in addition to postgres checkpoint parameters. Linux(Redhat 8), some OS kernel parameters need to be set ,right?

 

vm.dirty_expire_centisecs=500

vm.dirty_writeback_centisecs=250

vm.dirty_ratio=30

vm.dirty_background_ratio = 10

 


I understand the big picture (more-or-less), not tuning specifics.  But for a checkpoint we don't really give the O/S much control - it needs to do fsync when we ask for it.  It's in between the explicit issuance of checkpoints that the algorithms written into PostgreSQL and the O/S come into play to hopefully spread out the load over more time and keep the active memory holding useful data.

David J.

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