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

On 2017-04-13 14:05:43 -0400, Tom Lane wrote:
> Andres Freund <andres@anarazel.de> writes:
> > On 2017-04-13 12:56:14 -0400, Tom Lane wrote:
> >> Andres Freund <andres@anarazel.de> writes:
> >>> Cool.  I wonder if we also should remove AtEOXact_CatCache()'s
> >>> cross-checks - the resowner replacement has been in place for a while,
> >>> and seems robust enough.  They're now the biggest user of time.
> 
> >> Hm, biggest user of time in what workload?  I've not noticed that
> >> function particularly.
> 
> > Just initdb.  I presume it's because the catcaches will frequently be
> > relatively big there.
> 
> Hm.  That ties into something I was looking at yesterday.  The only
> reason that function is called so much is that bootstrap mode runs a
> separate transaction for *each line of the bki file* (cf do_start,
> do_end in bootparse.y).  Which seems pretty silly.

Indeed.


> On the whole, though, we may be looking at diminishing returns here.
> I just did some "perf" measurement of the overall "initdb" cycle,
> and what I'm seeing suggests that bootstrap mode as such is now a
> pretty small fraction of the overall cycle:
> 
> +   51.07%     0.01%            28  postgres         postgres                                      [.] PostgresMain
                  #
 
> ...
> +   13.52%     0.00%             0  postgres         postgres                                      [.]
AuxiliaryProcessMain             #
 
> 
> That says that the post-bootstrap steps are now the bulk of the time,
> which agrees with naked-eye observation.

The AtEOXact_CatCache weren't only in bootstrap mode, but yea, it's by
far smaller wins in comparison to the regprocin thing.

Greetings,

Andres Freund