| From: | David Rowley <dgrowleyml(at)gmail(dot)com> |
|---|---|
| To: | gzh <gzhcoder(at)126(dot)com> |
| Cc: | Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at>, pgsql-general(at)lists(dot)postgresql(dot)org |
| Subject: | Re: How to improve the performance of my SQL query？ |
| Date: | 2023-07-27 03:36:20 |
| Message-ID: | CAApHDvq08k_iJb8sCCAVPdV8A9JL0hEWFvs=3ryYsx3dApVOQQ@mail.gmail.com |
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| Lists: | pgsql-general |
On Wed, 26 Jul 2023 at 19:46, gzh <gzhcoder(at)126(dot)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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