On 3 September 2015 at 22:17, Andres Freund <and...@anarazel.de> wrote:
> On 2015-09-03 16:28:40 +1200, David Rowley wrote: > > I experimented with finding the fastest way to convert an int to a string > > at the weekend, I did happen to be testing with int64's but likely int32 > > will be the same. > > > > This is the time taken to convert 30 into "30" 2 billion times. > > > > The closest implementation I'm using in the patch is pg_int64tostr() one. > > The pg_int64tostr_memcpy() only performs better with bigger numbers / > > longer strings. > > > > david@ubuntu:~/C$ gcc5.2 tostring.c -o tostring -O2 > > david@ubuntu:~/C$ ./tostring > > pg_int64tostr_memcpy in 13.653252 seconds > > pg_int64tostr in 2.042616 seconds > > pg_int64tostr_new in 2.056688 seconds > > pg_lltoa in 13.604653 seconds > > > > david@ubuntu:~/C$ clang tostring.c -o tostring_clang -O2 > > david@ubuntu:~/C$ ./tostring_clang > > pg_int64tostr_memcpy in 0.000004 seconds > > pg_int64tostr in 2.063335 seconds > > pg_int64tostr_new in 2.102068 seconds > > pg_lltoa in 3.424630 seconds > > Are you sure this isn't an optimization artifact where the actual work > is optimized away? Doing 2 billion conversions in 2s kinda implies that > the string conversion is done in ~4 cycles. That seems unrealistically > fast, even for a pipelined cpu. > I think you're right. If I change the NUM_TO_STRING in my tostring.c to #define NUM_TO_PRINT i%100 I just wanted a way to keep the strings 2 digits long, so that it matches what will happen when building timestamps. It looks a bit different, but it's still a bit faster than pg_lltoa() david@ubuntu:~/C$ ./tostring pg_int64tostr_memcpy in 16.557578 seconds pg_int64tostr in 8.070706 seconds pg_int64tostr_new in 7.597320 seconds pg_lltoa in 12.315339 seconds david@ubuntu:~/C$ ./tostring_clang pg_int64tostr_memcpy in 19.698807 seconds pg_int64tostr in 12.800270 seconds pg_int64tostr_new in 14.174052 seconds pg_lltoa in 14.427803 seconds Regards David Rowley -- David Rowley http://www.2ndQuadrant.com/ <http://www.2ndquadrant.com/> PostgreSQL Development, 24x7 Support, Training & Services
