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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andres Freund <andres@anarazel.de>
Cc: Robert Haas <robertmhaas@gmail.com>
Cc: Васильев Дмитрий <d.vasilyev@postgrespro.ru>
Cc: pgsql-hackers@postgresql.org
Subject: Re: Performance degradation in commit ac1d794
Date: Thu, 14 Jan 2016 10:14:43 -0500
Message-ID: <19268.1452784483@sss.pgh.pa.us> (raw)
In-Reply-To: <20160114143931.GG10941@awork2.anarazel.de>
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Andres Freund <andres@anarazel.de> writes:
> 0004 currently contains one debatable optimization, which I'd like to
> discuss: Currently the 'sock' passed to WaitLatchOrSocket is not
> removed/added to the epoll fd, if it's the numerically same as in the
> last call. That's good for performance, but would be wrong if the socket
> were close and a new one with the same value would be waited on.  I
> think a big warning sign somewhere is sufficient to deal with that
> problem - it's not something we're likely to start doing. And even if
> it's done at some point, we can just offer an API to reset the last used
> socket fd.

Perhaps a cleaner API solution would be to remove the socket argument per
se from the function altogether, instead providing a separate
SetSocketToWaitOn() call.

(Also, if there is a need for it, we could provide a function that still
takes a socket argument, with the understanding that it's to be used for
short-lived sockets where you don't want to change the process's main
epoll state.)

			regards, tom lane


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