RE: Cache Hit Ratio% - Mailing list pgsql-admin

Thanks Fabio for your help.

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

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.pardi@portavita.eu>; pgsql-admin@lists.postgresql.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

 

From: Fabio Pardi <f.pardi@portavita.eu>
Sent: dinsdag 28 juli 2020 10:13
To: pgsql-admin@lists.postgresql.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.bhattacharjee@kpn.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