Re: Overhauling GUCS

On Fri, 6 Jun 2008, Peter Eisentraut wrote:

> - What settings do "newbies" (or anyone else) typically need to change?
> Please post a list.
> - What values would you set those settings to? Please provide a description
> for arriving at a value, which can later be transformed into code. Note that
> in some cases, not even the documentation provides more than handwaving help.

Josh's spreadsheet at
http://pgfoundry.org/docman/view.php/1000106/84/calcfactors.sxc provides
five different models for setting the most critical parameters based on
different types of workloads. Everyone can quibble over the fine tuning,
but having a good starter set of reasonable settings for these parameters
is a solved problem. It's just painful to build a tool to apply the
available expert knowledge that is already around.

> - If we know better values, why don't we set them by default?

Because there's not enough information available; the large differences
between how you tune for different workloads is one example. Another is
that people tune for peak and projected activity rather than just what's
happening right now. Every model suggested for a tuning wizard recognizes
you need to ask some set of questions to nail things down. I continue to
repeat in broken-record style, exactly what a tuning tool will ask about
and what settings it will suggest is not important, and getting into that
is an entirely different discussion (one that gets hashed out every single
day on pgsql-performance). The fact that writing such a tool is harder
than it should be is the issue here.

> Another orthogonal stumbling block on the way to making all of this
> automatic is that the surely criticial shared_buffers setting will in
> any useful configuration require messing around with kernel settings
> that no PostgreSQL tool can really help with.

Yes. So? All you can do is point this out to users.

--
* Greg Smith gsmith(at)gregsmith(dot)com http://www.gregsmith.com Baltimore, MD