| From: | Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> |
|---|---|
| To: | emil(at)iggland(dot)com, pgsql-bugs(at)lists(dot)postgresql(dot)org, Surafel Temesgen <surafel3000(at)gmail(dot)com>, David Christensen <david(dot)christensen(at)crunchydata(dot)com> |
| Subject: | Re: BUG #17141: SELECT LIMIT WITH TIES FOR UPDATE SKIP LOCKED returns wrong number of rows |
| Date: | 2021-08-11 20:07:09 |
| Message-ID: | 202108112007.evylbmzueapg@alvherre.pgsql |
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| Lists: | pgsql-bugs |
On 2021-Aug-11, PG Bug reporting form wrote:
> BEGIN;
> SELECT * FROM queue
> ORDER BY task DESC
> FETCH FIRST 1 ROWS WITH TIES
> FOR UPDATE SKIP LOCKED;
> /* Some work to be done here */
> COMMIT;
>
> select version();
> PostgreSQL 13.3, compiled by Visual C++ build 1914, 64-bit
>
> Expected result Worker 1: (580), (580), Actual result Worker 1: (580), (580)
> Expected result Worker 2: (480), (480), Actual result Worker 2: (480)
Ouch, we already saw this actually:
https://postgr.es/m/16676-fd62c3c835880da6@postgresql.org
The problem is that the first worker locks the first (480) row (even
though it does not return it), so the second worker skips it due to SKIP
LOCKED.
I have this on my list of things to look at, but it's not at the top
yet sadly ...
--
Álvaro Herrera
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