stray SIGALRM

In 9.3beta1, a backend will receive a SIGALRM after authentication_timeout
seconds, even if authentication has been successful. Most of the time
this doesn't hurt anyone, but there are cases, such as when the backend
is doing the open() of a backend copy, when it breaks things and results
in an error getting reported to the client. In particular, if you're doing
a copy from a FIFO, it is normal for open() to block until the process at
the other end has data ready, so you're very likely to have it interrupted
by the SIGALRM and fail.

To see the SIGALRM just run psql then determine your backend's pid,
attach an strace to it, and wait 60 seconds, or whatever you've got
authentication_timeout set to.

This behaviour appears in 6ac7facdd3990baf47efc124e9d7229422a06452 as a
side-effect of speeding things up by getting rid of setitimer() calls;
it's not obvious what's a good way to fix it without losing the benefits
of that commit.

Thanks Alvaro and Andres for helping me get from "why is my copy getting
these signals" to understanding what's actually going on.

Richard

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Richard Poole http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services