Re: BUG #7670: BUG #7545: Unresponsive server with error log reporting: "poll() failed: Invalid argument"

Andres Freund <andres(at)2ndquadrant(dot)com> writes:
> On 2012-11-18 13:18:42 -0500, Tom Lane wrote:
>> Well, we have two reports of people trying such values (assuming that
>> #7545 actually is the same thing), and it didn't work for either of
>> them. I don't think it's a problem to restrict the value to something
>> that will work rather than fail.

> Thats a good point. But #7545 was on OSX so its not really that much
> evidence a larger value doesn't work on non-bsdish systems.

> In fact, a setting of 32 days seems not to cause any immediate problems
> here on linux, even when choosing the timeout in a way it results in a
> negative timeout value for poll. Not sure what its waiting for, but it
> doesn't crash.

If you look closely at what's happening in syslogger.c, you'll realize
that it's a phase of the moon kind of behavior, because the
next_rotation_time is rounded off to a multiple of the specified
log_rotation_age. Then you'll get an overflow (or not) depending on
whether now() is within 2^31 msec of that target time. So for example
with a 30-day log_rotation_age, you'd be seeing failures during the
first five days of every "month", where a month is defined as
exactly-30-day intervals since the epoch. And I think there's a
timezone correction in there too, which would shift the trouble
intervals around for different people.

Anyway, even if Linux for some reason doesn't reject negative values,
I think we need to limit the GUC's range so we don't try to use them.
Maybe you'd get sane behavior and maybe you wouldn't. I notice that
the Single Unix Spec doesn't specify EINVAL for negative timeout
values, but it also doesn't define what happens for a negative value
other than -1. So this is basically an unspecified case and it's
incumbent on us to not do it if we want portable behavior.

regards, tom lane