| From: | Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> |
|---|---|
| To: | Alexander Lakhin <exclusion(at)gmail(dot)com> |
| Cc: | Jelte Fennema-Nio <postgres(at)jeltef(dot)nl>, Noah Misch <noah(at)leadboat(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Jacob Champion <jacob(dot)champion(at)enterprisedb(dot)com>, Denis Laxalde <denis(dot)laxalde(at)dalibo(dot)com>, vignesh C <vignesh21(at)gmail(dot)com>, Thomas Munro <thomas(dot)munro(at)gmail(dot)com>, Greg Stark <stark(at)mit(dot)edu>, "Gregory Stark (as CFM)" <stark(dot)cfm(at)gmail(dot)com>, Jelte Fennema <Jelte(dot)Fennema(at)microsoft(dot)com>, Daniel Gustafsson <daniel(at)yesql(dot)se>, Peter Eisentraut <peter(at)eisentraut(dot)org>, Andres Freund <andres(at)anarazel(dot)de>, Justin Pryzby <pryzby(at)telsasoft(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, pgsql-hackers(at)lists(dot)postgresql(dot)org, Etsuro Fujita <etsuro(dot)fujita(at)gmail(dot)com> |
| Subject: | Re: [EXTERNAL] Re: Add non-blocking version of PQcancel |
| Date: | 2024-07-16 15:08:52 |
| Message-ID: | 202407161508.qwzkqxsmjusg@alvherre.pgsql |
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| Lists: | pgsql-hackers |
On 2024-Jul-16, Alexander Lakhin wrote:
> I've managed to reproduce this issue in my Cygwin environment by running
> the postgres_fdw test in a loop (10 iterations are enough to get the
> described effect). And what I'm seeing is that a query-cancelling backend
> is stuck inside pgfdw_xact_callback() -> pgfdw_abort_cleanup() ->
> pgfdw_cancel_query() -> pgfdw_cancel_query_begin() -> libpqsrv_cancel() ->
> WaitLatchOrSocket() -> WaitEventSetWait() -> WaitEventSetWaitBlock() ->
> poll().
>
> The timeout value (approximately 30 seconds), which is passed to poll(),
> is effectively ignored by this call — the waiting lasts for unlimited time.
Ugh. I tried to follow what's going on in that cygwin code, but I gave
up pretty quickly. It depends on a mutex, but I didn't see the mutex
being defined or initialized anywhere.
> So it looks like a Cygwin bug, but maybe something should be done on our side
> too, at least to prevent such lorikeet failures.
I don't know what else we can do other than remove the test.
Maybe we can disable this test specifically on Cygwin. We could do that
by creating a postgres_fdw_cancel.sql file, with the current output for
all platforms, and a "SELECT version() ~ 'cygwin' AS skip_test" query,
as we do for encoding tests and such.
--
Álvaro Herrera Breisgau, Deutschland — https://www.EnterpriseDB.com/
"Doing what he did amounts to sticking his fingers under the hood of the
implementation; if he gets his fingers burnt, it's his problem." (Tom Lane)
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