| From: | Andres Freund <andres(at)anarazel(dot)de> |
|---|---|
| To: | Peter Geoghegan <pg(at)bowt(dot)ie> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Steven Winfield <Steven(dot)Winfield(at)cantabcapital(dot)com>, "pgsql-performance(at)lists(dot)postgresql(dot)org" <pgsql-performance(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: GCC 8.3.0 vs. 9.0.1 |
| Date: | 2019-05-07 17:42:47 |
| Message-ID: | 20190507174247.6s6qbmiwuzuoiaiz@alap3.anarazel.de |
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| Lists: | pgsql-performance |
Hi,
On 2019-05-07 10:28:16 -0700, Peter Geoghegan wrote:
> On Tue, May 7, 2019 at 10:06 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> > Given the described test setup, I'd put basically no stock in these
> > numbers. It's unlikely that this test case's performance is CPU-bound
> > per se; more likely, I/O and lock contention are dominant factors.
> > So I'm afraid whatever they're measuring is a more-or-less chance
> > effect rather than a real system-wide code improvement.
>
> Or a compiler bug. Link-time optimizations give the compiler a view of
> the program as a whole, not just a single TU at a time. This enables
> it to perform additional aggressive optimization.
Note that the flags described don't enable LTO.
Greetings,
Andres Freund
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