| From: | Jeff Janes <jeff(dot)janes(at)gmail(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Andrew Dunstan <andrew(dot)dunstan(at)2ndquadrant(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Invisible Indexes |
| Date: | 2018-07-08 14:52:38 |
| Message-ID: | CAMkU=1xdpFU_zQERoFK=mAs9Oit1RJ1+DuQ4QnEk994qdLr1Wg@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Mon, Jun 18, 2018 at 5:57 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
> I'm not sure about the "enforce constraint only" argument --- that
> sounds like a made-up use-case to me. It's pretty hard to imagine
> a case where a unique index applies to a query and yet you don't want
> to use it.
>
I've not seen it with unique constraints, but have with EXCLUDE
constraints. GiST index costing is not very robust, and the planner can
easily decide that a read query should use the EXCLUDE-supporting GiST
index in cases where it is not optimal.
Cheers,
Jeff
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