Re: any impact to DML sql statements when checkpoint starting

On Thu, Feb 3, 2022 at 5:45 PM James Pang (chaolpan) <chaolpan(at)cisco(dot)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.