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From: Tom Lane on 18 Dec 2009 12:52
Joshua Tolley <eggyknap(a)gmail.com> writes:
> On Fri, Dec 18, 2009 at 06:20:39PM +0100, Guillaume Lelarge wrote:
>> Le 18/12/2009 18:07, Tom Lane a �crit :
>>> On current Fedora 11, there is a huge difference in initdb time if you
>>> have TZ set versus if you don't: I get about 18 seconds versus less than
>>> four.

>> I have the exact same issue:

> For whatever it's worth, I get it too, on Ubuntu 9.04... ~4s without TZ vs.
> ~1.8s with TZ.

BTW, I just realized that it makes a difference that I customarily use
the configure option --with-system-tzdata=/usr/share/zoneinfo on that
machine. I do it mainly because it saves a few seconds during "make
install", but also because Red Hat's PG packages use that option so I
want to test it regularly. The impact of this is that the TZ search
also has to scan through a bunch of leap-second-aware timezone files,
which are not present in a default PG build's timezone tree. So that
probably explains why I see a 4x slowdown while you get more like 2x.
Still, it seems worth doing something about, if it's as easy as a
one-line addition.

regards, tom lane

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From: Tom Lane on 18 Dec 2009 12:57
Alvaro Herrera <alvherre(a)commandprompt.com> writes:
> I notice that most of the difference is system time ... I imagine we do
> a lot of syscalls to guess the timezone.

Yeah, it seems to be mostly the cost of searching the timezone directory
tree and reading all those small files. I was led to notice this
because Red Hat's latest devel kernels seem to have a bit of a
performance regression in this area:
https://bugzilla.redhat.com/show_bug.cgi?id=548403
Obviously there's something there for the kernel guys to fix, but
even with a non-borked kernel it's an expensive thing to do.

regards, tom lane

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From: Alex Hunsaker on 19 Dec 2009 16:12
On Fri, Dec 18, 2009 at 10:57, Tom Lane <tgl(a)sss.pgh.pa.us> wrote:
> Obviously there's something there for the kernel guys to fix, but
> even with a non-borked kernel it's an expensive thing to do.

Any thoughts on back patching this? While its not a bug per-say, it
seems reasonably low-risk. I for one would love a 2-4x initdb speedup
in the back branches :) Granted now I know I can just set TZ...

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