| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Thomas Munro <thomas(dot)munro(at)gmail(dot)com> |
| Cc: | Richard Guo <guofenglinux(at)gmail(dot)com>, "Gregory Stark (as CFM)" <stark(dot)cfm(at)gmail(dot)com>, Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>, Ronan Dunklau <ronan(dot)dunklau(at)aiven(dot)io>, Pg Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Emre Hasegeli <emre(at)hasegeli(dot)com> |
| Subject: | Re: Using each rel as both outer and inner for JOIN_ANTI |
| Date: | 2023-04-06 05:05:56 |
| Message-ID: | 2243123.1680757556@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Thomas Munro <thomas(dot)munro(at)gmail(dot)com> writes:
> ... It works if you're OK creating partial paths
> for everything...
Hmm. The committed patch already causes us to investigate more
paths than before, which I was okay with because it only costs
more if there's an antijoin involved --- which it seems like
there's at least a 50% chance of winning on, depending on which
table is bigger.
This:
> +#if 0
> /* If any limit was set to zero, the user doesn't want a
> parallel scan. */
> if (parallel_workers <= 0)
> return;
> +#endif
seems like it adds a lot of new paths with a lot lower chance
of win, but maybe we could tighten the conditions to improve
the odds?
regards, tom lane
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