Re: bgwriter_flush_after

Ok, thanks.

El jue, 14 oct 2021 a las 15:53, David G. Johnston (<
david(dot)g(dot)johnston(at)gmail(dot)com>) escribió:

> On Thursday, October 14, 2021, Henry Francisco Garcia Cortez <
> garcortez(at)gmail(dot)com> wrote:
>
>> I was reading about bgwriter_flush_after I found this website
>> https://postgreshelp.com/postgresql_shared_buffers/ however, I have some
>> questions:
>> First the parameter bgwriter_flush_after is amount of pages that
>> operating system’s cache could download to disk every time Fsync is called.
>> Second If I want to increase the parameter bgwriter_flush_after, for
>> instance to 2MB Will I get a better performance? and
>> Finally, What will be the cons of increasing this parameter?
>>
>>
> Pushing cache data to disk consumes I/O bandwidth. If a page is updated
> it eventually has to be pushed to disk. However, if it is updated again
> before that mandatory flush only the final version needs to be written. By
> attempting to spread out the I/O there is a decreased chance for that
> efficiency to happen. Instead, the first update gets flushed well before
> the mandatory time and then the second update also gets flushed. Thus the
> total I/O consumed is double, though this is mitigated by the fact the time
> period considered is spread out.
>
> The benefits are circumstantial, which basically means figure out you have
> a problem first then see whether this knob can help alleviate it. Though I
> suppose there may be some useful guidelines to consider; I’m just not aware
> of them.
>
> David J.
>
>

--
Ing. Henry G. Cortez