Re: Persistent wait event sets and socket changes

From: Andres Freund <andres(at)anarazel(dot)de>
To: Craig Ringer <craig(at)2ndquadrant(dot)com>
Cc: PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Persistent wait event sets and socket changes
Date: 2017-07-31 15:41:21
Views: Raw Message | Whole Thread | Download mbox | Resend email
Lists: pgsql-hackers

Hi Craig,

On 2017-07-31 14:08:58 +0800, Craig Ringer wrote:
> Hi all
> I've been looking into the wait event set interface added in 9.6 with an
> eye to using it in an extension that maintains a set of non-blocking libpq
> connections to other PostgreSQL instances.
> In the process I've been surprised to find that there does not appear to be
> any interface to remove a socket once added to the wait event set, or
> replace it with a new socket.
> ModifyWaitEvent(...) doesn't take a pgsocket. There doesn't seem to be a
> way to remove an event from the set either.

Yea, and what's even more annoying, you can't "disable" waiting for
readyness events on a socket, we've an assert that we're waiting for

> Discussion in
> talks about a proposed SetSocketToWaitOn(...)/AddSocketToWaitSet and
> RemoveSocketFromWaitSet etc. But it looks like it petered out and went
> nowhere, apparently mainly due to not being needed by any current core
> users.

I think it just needs somebody to push this forward.

> I'd like to add such interfaces at some point, but for now can work around
> it by destroying and re-creating the wait event set when the fd-set
> changes. So I'm posting mostly to confirm that it's not supposed to work,
> and ask if anyone thinks I should submit a comment patch to latch.c
> documenting it.

It doesn't work, right. I'm not sure I see the point of adding comments
explaining that a nonexistant interface doesn't exist?


Andres Freund

In response to

Browse pgsql-hackers by date

  From Date Subject
Next Message Sokolov Yura 2017-07-31 15:56:20 Lazy hash table for XidInMVCCSnapshot (helps Zipfian a bit)
Previous Message Alvaro Herrera 2017-07-31 15:18:05 Re: GSoC 2017: Foreign Key Arrays