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Subject: Re: need suggestion on querying big tables
From: Scott Ribe <scott_ribe@elevated-dev.com>
In-Reply-To: <d926084d-63a7-854b-2d8d-459d33ec7f70@gmail.com>
Date: Tue, 6 Dec 2022 10:07:41 -0600
Cc: pgsql-admin@lists.postgresql.org
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Message-Id: <AF5ECE5E-E6BA-41DD-B644-EB92A870736A@elevated-dev.com>
References: 
 <CAJuN1jj6NQDUjbMH=n4zry10JMJEZ8bRi=j6uA-3_108-Tq9cQ@mail.gmail.com>
 <d926084d-63a7-854b-2d8d-459d33ec7f70@gmail.com>
To: Ron <ronljohnsonjr@gmail.com>
Archived-At: 
 <https://www.postgresql.org/message-id/AF5ECE5E-E6BA-41DD-B644-EB92A870736A%40elevated-dev.com>
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> On Dec 6, 2022, at 8:51 AM, Ron <ronljohnsonjr@gmail.com> wrote:
>=20
> https://www.postgresql.org/docs/11/runtime-config-query.html
>=20
> effective_cache_size is how much RAM a single query gets.  "When =
setting this parameter you should consider both PostgreSQL's shared =
buffers".
>=20
> https://www.postgresql.org/docs/11/runtime-config-resource.html
>=20
> "a reasonable starting value for shared_buffers is 25% of the memory =
in your system. There are some workloads where even larger settings for =
shared_buffers are effective, but because PostgreSQL also relies on the =
operating system cache, it is unlikely that an allocation of more than =
40% of RAM to shared_buffers will work better than a smaller amount."
>=20
> You've set effective_cache_size to 83%, when it should be at most 20%.

effective_cache_size is a hint as to how much RAM is available for the =
operating system file cache after all other uses are taken into account.=