Re: walsender doesn't send keepalives when writes are pending

On 2014-02-14 12:55:06 +0000, Greg Stark wrote:
> On Fri, Feb 14, 2014 at 12:05 PM, Andres Freund <andres@2ndquadrant.com> wrote:
> > There's no reason not
> > to ask for a ping when we're writing.

> Is there a reason to ask for a ping? The point of keepalives is to
> ensure there's some traffic on idle connections so that if the
> connection is dead it doesn't linger forever and so that any on-demand
> links (or more recently NAT routers or stateful firewalls) don't time
> out and disconnect and have to reconnect (or more recently just fail
> outright).

This ain't TCP keepalives. The reason is that we want to kill walsenders
if they haven't responded to a ping inside wal_sender_timeout. That's
rather important e.g. for sychronous replication, so we can quickly fall
over to the next standby. In such scenarios you'll usually want a
timeout *far* below anything TCP provides.

Greetings,

Andres Freund

-- Andres Freund                       http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training &
Services