| From: | Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com> |
|---|---|
| To: | Michael Paquier <michael(dot)paquier(at)gmail(dot)com> |
| Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Amit Langote <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp>, Thom Brown <thom(at)linux(dot)com>, Jim Nasby <Jim(dot)Nasby(at)bluetreble(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Heikki Linnakangas <hlinnaka(at)iki(dot)fi>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>, Andres Freund <andres(at)anarazel(dot)de> |
| Subject: | Re: Proposal: "Causal reads" mode for load balancing reads without stale data |
| Date: | 2016-05-05 01:30:42 |
| Message-ID: | CAEepm=2zFZBYK-vRRi9nRmG3h_e0aCQM1C76bJYUwy_5AFo0Mg@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Tue, Mar 29, 2016 at 8:17 PM, Michael Paquier
<michael(dot)paquier(at)gmail(dot)com> wrote:
> On Tue, Mar 29, 2016 at 1:11 PM, Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com> wrote:
>> (BTW, isn't the select call in libpq_select
>> lacking an exceptfds set, and can't it therefore block forever when
>> there is an error condition on the socket and no timeout?)
>
> Hm. I think you're right here when timeout is NULL... It would loop infinitely.
> @Andres (in CC): your thoughts on that regarding the new
> WaitEventSetWaitBlock()? The same pattern is used there.
That was a red herring. I was confused because SUSv2 and POSIX call
this argument 'errorfds' and say that sockets *also* tell you about
errors this way. (Many/most real OSs call the argument 'exceptfds'
instead and only use it to tell you about out-of-band data and
possibly implementation specific events for devices, pseudo-terminals
etc. If you want to know about errors on a socket it's enough to have
it in readfds/writefds, and insufficient to have it only in
errorfds/exceptfds unless you can find a computer that actually
conforms to POSIX.)
--
Thomas Munro
http://www.enterprisedb.com
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