Re: Cutting initdb's runtime (Perl question embedded)

On 2017-04-17 17:49:54 +0100, Dagfinn Ilmari Mannsåker wrote:
> Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:
>
> > There's certainly lots more that could be done in the genbki code,
> > but I think all we can justify at this stage of the development
> > cycle is to get the low-hanging fruit for testing speedups.
>
> I threw Devel::NYTProf at it and picked some more low-hanging fruit.
> Attached are separate patches for each change, and here are the runtimes
> of genbki.pl and Gen_fmgrtab.pl, respectively, after each patch
> (averages of 5 runs, in millseconds):
>
> master (b6dd1271): 355, 182
>
> 1: Avoid unnecessary regex captures: 349, 183
> 2: Avoid repeated calls to SplitDataLine: 316, 158
> 3: Inline SplitDataLine: 291, 141
> 4: Inline check_natts: 287, 141
>
> Together they shave 68ms or 19.2% off the runtime of genbki.pl and 41ms
> or 22.5% off the runtime of Gen_fmgrtab.pl

I'm a bit doubtful about improving the performance of genbki at the cost
of any sort of complication - it's only executed during the actual
build, not during initdb... I don't see much point in doing things like
3) and 4), it's just not worth it imo.

- Andres