| From: | James Hunter <james(dot)hunter(dot)pg(at)gmail(dot)com> |
|---|---|
| To: | Tomas Vondra <tomas(at)vondra(dot)me> |
| Cc: | Richard Guo <guofenglinux(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Jeff Davis <pgsql(at)j-davis(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: should we have a fast-path planning for OLTP starjoins? |
| Date: | 2025-02-07 22:43:12 |
| Message-ID: | CAJVSvF7yu0fypZPymFRBJks4_Fg_TakxVgd5gJVNvCx8+0tdmw@mail.gmail.com |
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On Fri, Feb 7, 2025 at 12:09 PM Tomas Vondra <tomas(at)vondra(dot)me> wrote:
> ...
> Yes, I think that's pretty much the idea. Except that I don't think we
> need to look at the |F| at all - it will have more impact for small |F|,
> of course, but it doesn't hurt for large |F|.
>
> I think it'll probably need to consider which joins increase/decrease
> the cardinality, and "inject" the dimension joins in between those.
YMMV, but I suspect you may find it much easier to look at |F|, |F
JOIN D1|, |(F JOIN D1) JOIN D2|, etc., than to consider |F JOIN D1| /
|F|, etc. (In other words, I suspect that considering absolute
cardinalities will end up easier/cleaner than considering ratios of
increases/decreases in cardinalities.) But I have not thought about
this much, so I am not putting too much weight on my suspicions.
James
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