Keep in mind that if we auto-tune, we will only be able to do it for
some platforms, so we will need a table that shows which settings are
autotuned for each platform.


Sean Chittenden wrote:
> > I don't have much to add because I'm pretty new to Postgres and have
> > been soliciting advice here recently, but I totally agree with
> > everything you said.  I don't mind if it's in the postgres.conf file
> > or in a faq that is easy to find, I just would like it to be in one
> > place.  A good example of the need for this is when I was tuning
> > "effective_cache" I thought that was creating a cache for Postgres
> > when in fact as it was pointed out to me, it's just hinting to
> > postgres the size of the OS cache.  Lots of ways for people to get
> > really confused here.
> I looked through the src/doc/runtime.sgml for a good place to stick
> this and couldn't find a place that this seemed appropriate, but on
> FreeBSD, this can be determined with a great deal of precision in a
> programmatic manner:
> echo "effective_cache_size = $((`sysctl -n vfs.hibufspace` / 8192))"
> The same OID is available via C too.  It'd be slick if PostgreSQL
> could tune itself (on FreeBSD) at initdb time with the above code.  If
> Linux exports this info via /proc and can whip out the appropriate
> magic, even better.  An uncommented out good guess that shows up in
> postgresql.conf would be stellar and quite possible with the use of
> sed.
> Maybe an initdb switch could be added to have initdb tune the config
> it generates?  If a -n is added, have it generate a config and toss it
> to stdout?
> case `uname` in
> "FreeBSD")
>         echo "effective_cache_size = $((`sysctl -n vfs.hibufspace` / 8192))"
>         ;;
> *)
>         echo "Unable to automatically determine the effective cache size" >> 
> /dev/stderr
>         ;;
> esac
> -sc
> -- 
> Sean Chittenden
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