Re: Setting BLCKSZ 4kB

Hi Sanyam,

Interesting topic!

2018-01-16 7:50 GMT+01:00 sanyam jain <sanyamjain22(at)live(dot)in>:

> Hi,
>
> I am trying to solve WAL flooding due to FPWs.
>
>
> What are the cons of setting BLCKSZ as 4kB?
>
>
> When saw the results published on http://blog.coelho.net/
> database/2014/08/17/postgresql-page-size-for-SSD-2.html
>
> 4kB page is giving better performance in comparison to 8kB except when
> tested with 15kB row size.
>
>
> Does turning off FPWs will be safe if BLCKSZ is set to 4kB given page size
> of file system is 4kB?
>

There is this interesting article of Tomas Vondra:

https://blog.2ndquadrant.com/on-the-impact-of-full-page-writes/

that explains some consequences turning off full_page_writes. If I
correctly understood, turning off full_page_writes with BLCKSZ set to 4kB
can reduce
significantly the amount of produced WAL, but you cannot be sure that you
are completely safe with a PostgreSQL page that can be completely contained
in a 4kB file system page, though modern ones are less vulnerable to
partial writes.

In the article, Tomas focus the attention on the fact that most of full
page writes happens right after a checkpoint: a proper tuning of checkpoint
can help
reducing the amount of writes on the storage, continuing to safely keep
full_page_writes enabled.

Giuseppe.