Josh Berkus has already mentioned this as conventional wisdom as written
by Oracle. This may also be legacy wisdom. Oracle/Sybase/etc has been
around for a long time; it was probably a clear performance win way back
when. Nowadays with how far open-source OS's have advanced, I'd take it
with a grain of salt and do my own performance analysis. I suspect the
big vendors wouldn't change their stance even if they knew it was no
longer true due to the support hassles.
Reinvent a filesystem... that would be suicidal.
Now, Hans Reiser has expressed interest on the ReiserFS list in tweaking
his Reiser4 especially for Postgres. In his own words, he wants a "Killer
app for reiser4". Reiser4 will offser transactional semantics via a
special reiser4 syscall, so it might be possible, with a minimum of
changes to postgres (ie maybe just another sync mode besides fsync,
fdatasync et al) to use this. Other interesting details were exposed on
the reiser list, too (ie. a transactional filesystems can give ACID
guarantees to postgres without the need for fsync()).
Very interesting.
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TIP 2: Don't 'kill -9' the postmaster