Re: pgbench: could not connect to server: Resource temporarily unavailable

Just curious, *backlog* defines the maximum pending connections,
why do we need to double the MaxConnections as the queue size?
It seems *listen* with larger *backlog* will tell the OS maintain a
larger buffer?

- maxconn = MaxBackends * 2;
- if (maxconn > PG_SOMAXCONN)
- maxconn = PG_SOMAXCONN;
+ maxconn = MaxConnections * 2;

On Tue, Aug 23, 2022 at 12:57 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
> OK, here's some proposed patches.
>
> 0001 adds a para about how to raise the listen queue length.
>
> 0002 isn't quite related, but while writing 0001 I noticed a nearby
> use of /proc/sys/... which I thought should be converted to sysctl.
> IMO /proc/sys pretty much sucks, at least for documentation purposes,
> for multiple reasons:
>
> * It's unlike the way you do things on other platforms.
>
> * "man sysctl" will lead you to useful documentation about how to
> use that command. There's no obvious way to find documentation
> about /proc/sys.
>
> * It's not at all sudo-friendly. Compare
> sudo sh -c 'echo 0 >/proc/sys/kernel/randomize_va_space'
> sudo sysctl -w kernel.randomize_va_space=0
> The former is a lot longer and it's far from obvious why you have
> to do it that way.
>
> * You have to think in sysctl terms anyway if you want to make the
> setting persist across reboots, which you almost always do.
>
> * Everywhere else in runtime.sgml, we use sysctl not /proc/sys.
>
> 0003 removes PG_SOMAXCONN. While doing that I noticed that this
> computation hadn't been touched throughout all the various
> changes fooling with exactly what gets counted in MaxBackends.
> I think the most appropriate definition for the listen queue
> length is now MaxConnections * 2, not MaxBackends * 2, because
> the other processes counted in MaxBackends don't correspond to
> incoming connections.
>
> I propose 0003 for HEAD only, but the docs changes could be
> back-patched.
>
> regards, tom lane
>

--
Regards
Junwang Zhao