On Thu, 20 Jul 2023 at 20:37, Dean Rasheed <dean.a.rash...@gmail.com> wrote: > > On Thu, 20 Jul 2023 at 00:56, David Rowley <dgrowle...@gmail.com> wrote: > I agree with the principal though. In the attached updated patch, I > replaced that test with a simpler one: > > + /* > + * Process the number's digits. We optimize for decimal input (expected > to > + * be the most common case) first. Anything that doesn't start with a > base > + * prefix indicator must be decimal. > + */ > + > + /* process decimal digits */ > + if (likely(ptr[0] != '0' || !isalpha((unsigned char) ptr[1]))) > > So hopefully any compiler should only need to do the one comparison > against '0' for any non-zero decimal input. > > Doing that didn't give any measurable performance improvement for me, > but it did at least not make it noticeably worse, and seems more > likely to generate better code with not-so-smart compilers. I'd be > interested to know how that performs for you (and if your compiler > really does generate 3 "first digit is '0'" tests for the unpatched > code).
That seems better. I benchmarked it on two machines: gcc12.2/linux/amd3990x create table a (a int); insert into a select x from generate_series(1,10000000)x; copy a to '/tmp/a.dump'; master @ ab29a7a9c postgres=# truncate a; copy a from '/tmp/a.dump'; Time: 2226.912 ms (00:02.227) Time: 2214.168 ms (00:02.214) Time: 2206.481 ms (00:02.206) Time: 2219.640 ms (00:02.220) Time: 2205.004 ms (00:02.205) master + pg_strtoint32_base_10_first.v2.patch postgres=# truncate a; copy a from '/tmp/a.dump'; Time: 2067.108 ms (00:02.067) Time: 2070.401 ms (00:02.070) Time: 2073.423 ms (00:02.073) Time: 2065.407 ms (00:02.065) Time: 2066.536 ms (00:02.067) (~7% faster) apple m2 pro/clang master @ 9089287a postgres=# truncate a; copy a from '/tmp/a.dump'; Time: 1286.369 ms (00:01.286) Time: 1300.534 ms (00:01.301) Time: 1295.661 ms (00:01.296) Time: 1296.404 ms (00:01.296) Time: 1268.361 ms (00:01.268) Time: 1259.321 ms (00:01.259) master + pg_strtoint32_base_10_first.v2.patch postgres=# truncate a; copy a from '/tmp/a.dump'; Time: 1253.519 ms (00:01.254) Time: 1235.256 ms (00:01.235) Time: 1269.501 ms (00:01.270) Time: 1267.801 ms (00:01.268) Time: 1275.758 ms (00:01.276) Time: 1261.478 ms (00:01.261) (a bit noisy but avg of ~1.8% faster) David
