Implement support for TCP_KEEPCNT, TCP_KEEPIDLE, TCP_KEEPINTVL (was Re: [HACKERS] Feature freeze date for 8.1)

Tom Lane wrote:
> Oliver Jowett <oliver(at)opencloud(dot)com> writes:
>
>>Tom Lane wrote:
>>
>>>I'm not convinced that Postgres ought to provide
>>>a way to second-guess the TCP stack ...
>
>
>>Would you be ok with a patch that allowed configuration of the
>>TCP_KEEPCNT / TCP_KEEPIDLE / TCP_KEEPINTVL socket options on backend
>>sockets?
>
>
> [ shrug... ] As long as it doesn't fail to build on platforms that
> don't offer those options, I couldn't complain too hard. But do we
> really need all that?

Here's a patch that adds four new GUCs:

tcp_keepalives (defaults to on, controls SO_KEEPALIVE)
tcp_keepalives_idle (controls TCP_KEEPIDLE)
tcp_keepalives_interval (controls TCP_KEEPINTVL)
tcp_keepalives_count (controls TCP_KEEPCNT)

They're ignored for AF_UNIX connections and when running standalone.

tcp_keepalives_* treat 0 as "use system default". If the underlying OS
doesn't provide the TCP_KEEP* socket options, the GUCs are present but
reject any value other than 0.

SHOW reflects the currently-in-use value or 0 if not applicable or not
known. i.e. if you set it to 0 and you have the socket options
available, SHOW will show the result of getsockopt() which is non-zero.

A default install on my Linux system produces:

template1=# show all;
name | setting

--------------------------------+----------------------------------------------
[...]
tcp_keepalives | on
tcp_keepalives_count | 9
tcp_keepalives_idle | 7200
tcp_keepalives_interval | 75
[...]

I haven't had a chance to check it builds on other systems or to test
that this handles actual network failures nicely yet.

-O