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
Simplest way may be to create a 'auto-tune' directory with scripts for configured platforms. When postgres installs the databases, it checks for 'tune.xxx' and if found uses that to generate the script itself?
This would allow for defaults on platforms that do not have them and optimization for those that do.
Martin Foster
Creator/Designer Ethereal Realms
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