Re: Keepalive for max_standby_delay

Stephen Frost <sfrost@snowman.net> writes:
> * Tom Lane (tgl@sss.pgh.pa.us) wrote:
>> Comments?

> I'm not really a huge fan of adding another GUC, to be honest.  I'm more
> inclined to say we treat 'max_archive_delay' as '0', and turn
> max_streaming_delay into what you've described.  If we fall back so far
> that we have to go back to reading WALs, then we need to hurry up and
> catch-up and damn the torpedos.

If I thought that 0 were a generally acceptable value, I'd still be
pushing the "simplify it to a boolean" agenda ;-).  The problem is that
that will sometimes kill standby queries even when they are quite short
and doing nothing objectionable.

> I'd also prefer that we only wait the
> delay time once until we're fully caught up again (and have gotten
> back around to waiting for new data).  

The delays will be measured from a receipt instant to current time,
which means that the longer it takes to apply a WAL segment or WAL
send chunk, the less grace period there will be.  (Which is the
same as what CVS HEAD does --- I'm just arguing about where we get
the start time from.)  I believe this does what you suggest and more.
        regards, tom lane