Re: Hot Standby and deadlock detection

On Mon, 2010-02-01 at 09:40 +0200, Heikki Linnakangas wrote:
> Simon Riggs wrote:
> > The way this would work is if Startup waits on a buffer pin we
> > immediately send out a request to all backends to cancel themselves if
> > they are holding the buffer pin required && waiting on a lock. We then
> > sleep until max_standby_delay. When max_standby_delay = -1 we only sleep
> > until deadlock timeout and then check (on the Startup process).
> 
> Should wake up to check for deadlocks after deadlock_timeout also when
> max_standby_delay > deadlock_timeout. max_standby_delay could be hours -
> we want to detect a deadlock sooner than that.

The patch does detect deadlocks sooner that that - "immediately", as
described above.

The simplified logic is

if (MaxStandbyDelay == 0)immediate time out any buffer pin holders
else if (MaxStandbyDelay == -1)wait for deadlock_timeout then check for deadlockers
else if (standby_delay > MaxStandbyDelay)immediate time out on buffer pin
else
{immediate(*) check for deadlockerswait for remainder of time then time out any buffer pin holders
}

(*) Doing it this way makes the logic sigalarm handler code easier/more
bug free. The only difference is a potential performance gain from not
running deadlock detection early.

-- Simon Riggs           www.2ndQuadrant.com