Re: Cost of XLogInsert CRC calculations

On K, 2005-05-18 at 10:24 +0300, Hannu Krosing wrote:
> On T, 2005-05-17 at 22:37 -0400, Tom Lane wrote:
> > Bruce Momjian <pgman@candle.pha.pa.us> writes:
> > > I don't understand why we are testing 64-bit CRC when I thought we
> > > agreed that 32-bit was good enough for our purposes.
> > 
> > Well, we need to understand exactly what is going on here.  I'd not
> > like to think that we dropped back from 64 to 32 bit because of one
> > possibly-minor optimization bug in one compiler on one platform.
> > Even if that compiler+platform is 90% of the market.
> 
> There are cases where 32bit is about 20% slower.
> 
> I tried to send the folowing yesterday, but for some reason the mails I
> send from home where To: is Tom Lane get errors from
> "RCPT:tgl@sss.pgh.pa.us " and fail to go through to other destinations
> (like pgsql-hackers) after that :(
> -----

the same difference between 32bit and 64bit CRC when compiled as 64bit
exe is there also on ibms own compiler (vac xlc 7.0)

[hannu@power ~]$ c99 -O5 -qarch=pwr5 -qtune=pwr5 -qsmp=omp -qunroll=yes -q64 crctest64.c -o crctest64_c99_64
[hannu@power ~]$ ./crctest64_c99_64
Result of CRC64 (10000 runs): 782104059a01660 in time 0.545042 s
[hannu@power ~]$ c99 -O5 -qarch=pwr5 -qtune=pwr5 -qsmp=omp -qunroll=yes\-q64 crctest.c -o crctest_c99_64
[hannu@power ~]$ ./crctest_c99_64
Result of CRC64 (10000 runs): 7821040 (high), 59a01660 (low) in time
0.644319 s

> 
-- 
Hannu Krosing <hannu@skype.net>