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Re: Possible Bug: high CPU usage for stats collector in 8.2

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Andrew Dunstan <andrew(at)dunslane(dot)net>
Cc: Darcy Buskermolen <darcyb(at)commandprompt(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Possible Bug: high CPU usage for stats collector in 8.2
Date: 2007-03-01 20:42:29
Message-ID: 16546.1172781749@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Andrew Dunstan <andrew(at)dunslane(dot)net> writes:
> Good catch. I am also a bit dubious about this code:

>         input_fd.fd = pgStatSock;
>         input_fd.events = POLLIN | POLLERR;
>         input_fd.revents = 0;

Hm.  The Single Unix Spec saith that POLLERR is ignored in the events
field, but it is not clear to me that older systems might not treat it
as a condition bit.  For instance on HPUX the poll man page says only

     The condition flags POLLERR, POLLHUP, and POLLNVAL are always set in
     revents if the conditions they indicate are true for the specified
     file descriptor, whether or not these flags are set in events.

> AIUI you are not supposed to put POLLERR in the events field. We should 
> probably be setting POLLIN | POLLPRI,  and we should also probably check 
> exactly what event was returned in revents.

We don't need to check what was returned because the action is the same
either way: do a recv().  I'm not seeing the point of setting POLLPRI.

			regards, tom lane

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