Re: How to improve the performance of my SQL query? - Mailing list pgsql-general

From David Rowley
Subject Re: How to improve the performance of my SQL query?
Date
Msg-id CAApHDvq08k_iJb8sCCAVPdV8A9JL0hEWFvs=3ryYsx3dApVOQQ@mail.gmail.com
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In response to Re: How to improve the performance of my SQL query?  (gzh <gzhcoder@126.com>)
Responses Re: How to improve the performance of my SQL query?
List pgsql-general
On Wed, 26 Jul 2023 at 19:46, gzh <gzhcoder@126.com> wrote:
> QUERY PLAN (enable_seqscan=on)

> Execution Time: 167183.133 ms

> QUERY PLAN (enable_seqscan=off)

> Execution Time: 22320.153 ms

effective_cache_size and random_page_cost are the settings you should
be adjusting to coax the planner into using the index.

A rule of thumb for effective_cache_size would be to set it to about
75% of RAM. There are certainly cases where lower would make more
sense, certainly, 75% will make more sense than the default 4GB value
in the majority of cases.

For random_page_cost, the default of 4.0 has been the default since
HDDs were common. SSDs are common now and, comparatively to sequential
I/O, their random I/O is faster than that of an HDD, so you may get
better results by lowering random_page_cost.

David



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