From: Tom Lane <tgl@sss.pgh.pa.us>
To: Thomas Munro <thomas.munro@gmail.com>
cc: =?UTF-8?Q?R=C3=A9mi_Zara?= <remi_zara@mac.com>,
        Michael Paquier <michael@paquier.xyz>,
        PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: pgsql: Add kqueue(2) support to the WaitEventSet API.
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Comments: In-reply-to Thomas Munro <thomas.munro@gmail.com>
	message dated "Mon, 24 Feb 2020 19:53:34 +1300"
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Date: Mon, 24 Feb 2020 09:44:29 -0500
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Thomas Munro <thomas.munro@gmail.com> writes:
> I suppose there may be users who have set ulimit -n high enough to
> support an FDW workload that connects to very many hosts, who will now
> need to set max_files_per_process higher to avoid the new error now
> that we're doing this accounting.  That doesn't seem to be a problem
> in itself, but I wonder if the error message should make it clearer
> that it's our limit they hit here.

I struggled with the wording of that message, actually.  The patch
proposes

+            ereport(ERROR,
+                    (errcode(ERRCODE_SQLCLIENT_UNABLE_TO_ESTABLISH_SQLCON=
NECTION),
+                     errmsg("could not connect to server \"%s\"",
+                            server->servername),
+                     errdetail("There are too many open files.")));

I wanted to say "The server has too many open files." but in context
it would seem to be talking about the remote server, so I'm not sure
how to fix that.

We could also consider a HINT, along the lines of "Raise the server's
max_files_per_process and/or \"ulimit -n\" limits."  This again has
the ambiguity about which server, and it also seems dangerously
platform-specific.

			regards, tom lane