Re: Optimization levels when compiling PostgreSQL...

Tom Lane wrote:
> Sean Chittenden <sean(at)chittenden(dot)org> writes:
> > The size difference between -O and -O3 is only 200K or so... does
> > anyone think that it'd be safe to head to -O6 on a wide scale?
>
> Dunno. I'm not aware of any bits of the code that are unportable enough
> to break with max optimization of any correct compiler. But you might
> find such a bug. Or a bug in your compiler. Are you feeling lucky
> today?
>
> My feeling is that gcc -O2 is quite well tested with the PG code.
> I don't have any equivalent confidence in -O6. Give it a shot for
> beta-testing, for sure, but I'm iffy about calling that a
> production-grade database release...

And of course the big question is whether you will see any performance
improvement with -O6 vs. -O2. My guess is no.

>
> > I'm even thinking about going so far as to have flex required for the
> > build dependencies and setting -Cf or -CF for building the scanner
> > (need to check the archives for which turned out to be faster).
>
> Um, didn't we do that stuff already in the standard build? AFAIK
> you cannot build PG with any lexer except flex, and Peter already
> hacked the flags.

Yes, I thought that was a done deal too.

> > I'm also tinkering with the idea of automatically turn off fsync if
> > optimize is set.
>
> No-bloody-way. Trusting your compiler is an entirely separate issue
> from whether you trust your disk hardware, power source, etc. Puh-leez
> do not muddy the waters by introducing a port-specific variation in
> choices that only the DBA of a particular installation should make.

Tom is right. Hardware/power reliability is a different issue.

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