Re: Weird Unicorn Timeout Issues (Hibernation problem?)

[Eric Wong <e@80x24.org>]

Tony Devlin <tonydevlin@gmail.com> wrote:
> pid  7825] write(14,
> "\0\373\0\0\6\0\0\0\0\0\21iB\376\377\377\377\377\377\377\377\1\0\0\0\0\0\0\0\v\0\0\0\3^Ca\201\0\0\0\0\0\0\376\377\377\377\377\377\377\377\22\0\0\0\376\377\377\377\377\377\377\377\r\0\0\0\376\377\377\377\377\377\377\377\376\377\377\377\377\377\377\377\0\0\0\0d\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\376\377\377\377\377\377\377\377\0\0\0\0\0\0\0\0\376\377\377\377\377\377\377\377\376\377\377\377\377\377\377\377\376\377\377\377\377\377\377\377\0\0\0\0\0\0\0\0\376\377\377\377\377\377\377\377\376\377\377\377\377\377\377\377\22select
> 1 from
> dual\1\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\1\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0",
> 251) = 251
> [pid  7825] read(14,  <unfinished ...>
> [pid  7827] +++ killed by SIGKILL +++

Any update?  It looks like your DB driver is not using/respecting any
timeout at all[1].  It is bad to not have a timeout there.  There should
be a way to set a timeout so you can at least tell the user the DB
connection dropped or maybe get your app to disconnect+retry once.

A better looking strace would be something like:

    write(fd, ...); => success
    (poll|select|ppoll) syscall ...
    read(fd, ...); /* only if (poll|select|ppoll) was successful[2] */

This goes for configuring all connections/services for any app.

[1] or if it's relying on SO_RCVTIMEO socket option(rare), that's set
    way too high.  Any timeout set for any external connection should
    be lower than the unicorn (last-resort) timeout feature.

[2] any read() syscall after (poll|select|ppoll) should be non-blocking,
    because (poll|select|ppoll) may spuriously wakeup.