RE: Cache Hit Ratio%

Thanks Fabio for your help.

From: Fabio Pardi <f(dot)pardi(at)portavita(dot)eu>
Sent: dinsdag 28 juli 2020 11:46
To: Bhattacharjee, Soumik <soumik(dot)bhattacharjee(at)kpn(dot)com>; pgsql-admin(at)lists(dot)postgresql(dot)org
Subject: Re: Cache Hit Ratio%

Depending on your PostgreSQL RAM budget, you might want to increase the shared_buffers in order to be able to fit more in it.

If I were you, I would investigate the matter more in depth, and educate yourself on the subject.

You can get insights using pg_buffercache:

https://www.postgresql.org/docs/current/pgbuffercache.html

When in need, I also use the following query to understand how the buffers are rotating.

select usagecount,count(*),isdirty

from pg_buffercache

group by isdirty,usagecount

order by isdirty,usagecount ;

hope it helps.

regards,

fabio pardi

On 28/07/2020 11:18, soumik(dot)bhattacharjee(at)kpn(dot)com<mailto:soumik(dot)bhattacharjee(at)kpn(dot)com> wrote:
Hi,

This are the values for

* effective_cache_size = 6GB
* OS RAM = 25GB
Thanks..

From: Bhattacharjee, Soumik
Sent: dinsdag 28 juli 2020 10:36
To: Fabio Pardi <f(dot)pardi(at)portavita(dot)eu><mailto:f(dot)pardi(at)portavita(dot)eu>; pgsql-admin(at)lists(dot)postgresql(dot)org<mailto:pgsql-admin(at)lists(dot)postgresql(dot)org>
Subject: RE: Cache Hit Ratio%

Hi Fabio,

Its same across all env's

* Shared_buffers is 2GB
* DB size is same 12GB

Query Plan in PROD Env
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From: Fabio Pardi <f(dot)pardi(at)portavita(dot)eu<mailto:f(dot)pardi(at)portavita(dot)eu>>
Sent: dinsdag 28 juli 2020 10:13
To: pgsql-admin(at)lists(dot)postgresql(dot)org<mailto:pgsql-admin(at)lists(dot)postgresql(dot)org>
Subject: Re: Cache Hit Ratio%

Hi,

I would start checking (and comparing with pre-prod) the db size, the shared_buffers size, how much data end up in cache and how are the cache layer's used.

regards,

fabio pardi
On 28/07/2020 10:04, soumik(dot)bhattacharjee(at)kpn(dot)com<mailto:soumik(dot)bhattacharjee(at)kpn(dot)com> wrote:
Dear Experts,

We have done production migration from Oracle to PostgreSQL.

Could you please help me to know where to look out for - the Cache Hit Ratio is always at 65.72% , but in lower Pre-Prod env it's kind of 95%.

As such no major slowness is reported by the customer so far.

Thanks