Re: Re: [COMMITTERS] pgsql: Make CheckRequiredParameterValues() depend upon correct

Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> Nobody is proposing otherwise. What Simon and I are proposing is that
> if the master is configured to support HS, it comes up on the slave by
> default without requiring additional configuration. Now maybe that's
> too much spooky action at a distance, but I suspect it IS the behavior
> most people will want. If Tom and Heikki get their way and change the
> default behavior, it'll just mean (nearly) everyone flips one extra
> configuration switch.

We already bought into the "one extra switch" penalty when we agreed to
invent a separate wal_level parameter. The entire point of that was to
have more, but simpler-to-understand, parameters with fewer hidden
interactions. Arguing that there are now too many knobs to twiddle
amounts to trying to revisit that discussion, which we don't have time
for now.

>> That said, I'ld probalby be happy with PG 9 having a "default" config
>> of:
>> wal_mode = hot_standby
>> recovery_connections = on

> That would be a bad idea - there's a significant performance penalty
> from setting wal_level to anything other than minimal (just as there
> is for turning on archive_mode in 8.4).

There is not only a performance penalty, but a reliability penalty.
Enabling these switches turns on a whole lot of code that, with all
due respect to those who have worked on it, is absolutely positively
guaranteed to be full of bugs. Not all of which are going to be flushed
out during beta. If we ship 9.0 with these things on by default, it
will result in an immediate reliability downgrade for installations that
are simply doing what they did before and not even interested in HS/SR.

Maybe by 9.1 or 9.2 it would be sensible to have some of this code
turned on by default. But it is absolutely not in keeping with this
project's mindset or historical practice to enable it by default now.

regards, tom lane