Re: max_standby_delay considered harmful

Robert Haas wrote:
> On Wed, May 5, 2010 at 11:52 PM, Bruce Momjian <bruce@momjian.us> wrote:
>> I am afraid the current setting is tempting for users to enable, but
>> will be so unpredictable that it will tarnish the repuation of HS and
>> Postgres.  We don't want to be thinking in 9 months, "Wow, we shouldn't
>> have shipped that features.  It is causing all kinds of problems."  We
>> have done that before (rarely), and it isn't a good feeling.
> 
> I am not convinced it will be unpredictable.  The only caveats that
> I've seen so far are:
> 
> - You need to run ntpd.
> - Queries will get cancelled like crazy if you're not using steaming
> replication.

And also in situations where the master is idle for a while and then
starts doing stuff. That's the most significant source of confusion,
IMHO, I wouldn't mind the requirement of ntpd so much.

> That just doesn't sound that bad to me, especially since the proposed
> alternative is:
> 
> - Queries will get cancelled like crazy, period.
> 
> Or else:
> 
> - Replication can fall infinitely far behind and you can write a
> tedious and error-prone script to try to prevent it if you like.
> 
> I think THAT is going to tarnish our reputation.

The difference is that that's easy to document and understand, so the
behavior won't be a surprise to anyone.

--  Heikki Linnakangas EnterpriseDB   http://www.enterprisedb.com