Re: Shared_buffers

[MichaelDBA]

Here's one cook article on using pg_buffercache...

https://www.keithf4.com/a-large-database-does-not-mean-large-shared_buffers/

Regards,
Michael Vitale


Justin Pryzby 
Tuesday, March 12, 2019 4:11 PM

I've tuned ~40 postgres instances, primarily using log_checkpoints and
pg_stat_bgwriter, with custom RRD graphs. pg_buffercache does provide some
valuable insights, and I know it's commonly suggested to check 
histogram of

usagecounts, but I've never had any idea how to apply that to tune
shared_buffers.

Could you elaborate on what procedure you suggest ?

Justin
MichaelDBA 
Tuesday, March 12, 2019 4:03 PM
Set shared_buffers more accurately by using pg_buffercache extension 
and the related queries during high load times.


Regards,
Michael Vitale


Michael Lewis 
Tuesday, March 12, 2019 3:23 PM
On Tue, Mar 12, 2019 at 2:29 AM Laurenz Albe > wrote:


Daulat Ram wrote:
> I want to know about the working and importance of
shared_buffers  in Postgresql?
> is it similar to the oracle database buffer cache?

Yes, exactly.

The main difference is that PostgreSQL uses buffered I/O, while
Oracle usually
uses direct I/O.

Usually you start with shared_buffers being the minimum of a
quarter of the
available RAM and 8 GB.


Any good rule of thumb or write up about when shared buffers in excess 
of 8GBs makes sense (assuming system ram 64+ GBs perhaps)?

Re: Shared_buffers

[Justin Pryzby]

On Tue, Mar 12, 2019 at 04:03:11PM -0400, MichaelDBA wrote:
> Set shared_buffers more accurately by using pg_buffercache extension and the
> related queries during high load times.

I've tuned ~40 postgres instances, primarily using log_checkpoints and
pg_stat_bgwriter, with custom RRD graphs.  pg_buffercache does provide some
valuable insights, and I know it's commonly suggested to check histogram of
usagecounts, but I've never had any idea how to apply that to tune
shared_buffers.

Could you elaborate on what procedure you suggest ?

Justin

Re: Shared_buffers

[MichaelDBA]

Set shared_buffers more accurately by using pg_buffercache extension and 
the related queries during high load times.


Regards,
Michael Vitale


Michael Lewis 
Tuesday, March 12, 2019 3:23 PM
On Tue, Mar 12, 2019 at 2:29 AM Laurenz Albe > wrote:


Daulat Ram wrote:
> I want to know about the working and importance of
shared_buffers  in Postgresql?
> is it similar to the oracle database buffer cache?

Yes, exactly.

The main difference is that PostgreSQL uses buffered I/O, while
Oracle usually
uses direct I/O.

Usually you start with shared_buffers being the minimum of a
quarter of the
available RAM and 8 GB.


Any good rule of thumb or write up about when shared buffers in excess 
of 8GBs makes sense (assuming system ram 64+ GBs perhaps)?

Re: Shared_buffers

[Michael Lewis]

On Tue, Mar 12, 2019 at 2:29 AM Laurenz Albe 
wrote:

> Daulat Ram wrote:
> > I want to know about the working and importance of shared_buffers  in
> Postgresql?
> > is it similar to the oracle database buffer cache?
>
> Yes, exactly.
>
> The main difference is that PostgreSQL uses buffered I/O, while Oracle
> usually
> uses direct I/O.
>
> Usually you start with shared_buffers being the minimum of a quarter of the
> available RAM and 8 GB.
>

Any good rule of thumb or write up about when shared buffers in excess of
8GBs makes sense (assuming system ram 64+ GBs perhaps)?

Re: Shared_buffers

[Laurenz Albe]

Daulat Ram wrote:
> I want to know about the working and importance of shared_buffers  in 
> Postgresql?
> is it similar to the oracle database buffer cache?

Yes, exactly.

The main difference is that PostgreSQL uses buffered I/O, while Oracle usually
uses direct I/O.

Usually you start with shared_buffers being the minimum of a quarter of the
available RAM and 8 GB.

Yours,
Laurenz Albe
-- 
Cybertec | https://www.cybertec-postgresql.com