On 2018-09-26 15:04:20 -0700, Andres Freund wrote: > On 2018-09-12 14:14:15 -0400, Tom Lane wrote: > > Alexander Kuzmenkov <a.kuzmen...@postgrespro.ru> writes: > > > I benchmarked this, using your testbed and comparing to libc sprintf > > > (Ubuntu GLIBC 2.27-0ubuntu3) and another implementation I know [1], all > > > compiled with gcc 5. > > > > Thanks for reviewing! > > > > The cfbot noticed that the recent dlopen patch conflicted with this in > > configure.in, so here's a rebased version. The code itself didn't change. > > Conflicts again, but not too hard to resolve. > > The mini benchmark from > http://archives.postgresql.org/message-id/20180926174645.nsyj77lx2mvtz4kx%40alap3.anarazel.de > is significantly improved by this patch. > > > 96bf88d52711ad3a0a4cc2d1d9cb0e2acab85e63: > > > > COPY somefloats TO '/dev/null'; > > COPY 10000000 > > Time: 24575.770 ms (00:24.576) > > > > 96bf88d52711ad3a0a4cc2d1d9cb0e2acab85e63^: > > > > COPY somefloats TO '/dev/null'; > > COPY 10000000 > > Time: 12877.037 ms (00:12.877) > > This patch: > > postgres[32704][1]=# ;SELECT pg_prewarm('somefloats');COPY somefloats TO > '/dev/null'; > Time: 0.269 ms > ┌────────────┐ > │ pg_prewarm │ > ├────────────┤ > │ 73530 │ > └────────────┘ > (1 row) > > Time: 34.983 ms > COPY 10000000 > Time: 15511.478 ms (00:15.511) > > > The profile from 96bf88d52711ad3a0a4cc2d1d9cb0e2acab85e63^ is: > + 38.15% postgres libc-2.27.so [.] __GI___printf_fp_l > + 13.98% postgres libc-2.27.so [.] hack_digit > + 7.54% postgres libc-2.27.so [.] __mpn_mul_1 > + 7.32% postgres postgres [.] CopyOneRowTo > + 6.12% postgres libc-2.27.so [.] vfprintf > + 3.14% postgres libc-2.27.so [.] __strlen_avx2 > + 1.97% postgres postgres [.] heap_deform_tuple > + 1.77% postgres postgres [.] AllocSetAlloc > + 1.43% postgres postgres [.] psprintf > + 1.25% postgres libc-2.27.so [.] _IO_str_init_static_internal > + 1.09% postgres libc-2.27.so [.] _IO_vsnprintf > + 1.09% postgres postgres [.] appendBinaryStringInfo > > The profile of master with this patch is: > > + 32.38% postgres libc-2.27.so [.] __GI___printf_fp_l > + 11.08% postgres libc-2.27.so [.] hack_digit > + 9.55% postgres postgres [.] CopyOneRowTo > + 6.24% postgres libc-2.27.so [.] __mpn_mul_1 > + 5.01% postgres libc-2.27.so [.] vfprintf > + 4.91% postgres postgres [.] dopr.constprop.4 > + 3.53% postgres libc-2.27.so [.] __strlen_avx2 > + 1.55% postgres libc-2.27.so [.] __strchrnul_avx2 > + 1.49% postgres libc-2.27.so [.] __memmove_avx_unaligned_erms > + 1.35% postgres postgres [.] AllocSetAlloc > + 1.32% postgres libc-2.27.so [.] _IO_str_init_static_internal > + 1.30% postgres postgres [.] FunctionCall1Coll > + 1.27% postgres postgres [.] psprintf > + 1.16% postgres postgres [.] appendBinaryStringInfo > + 1.16% postgres libc-2.27.so [.] _IO_old_init > + 1.06% postgres postgres [.] heap_deform_tuple > + 1.02% postgres libc-2.27.so [.] sprintf > + 1.02% postgres libc-2.27.so [.] _IO_vsprintf > > (all functions above 1%) > > > I assume this partially is just the additional layers of function calls > (psprintf, pvsnprintf, pg_vsnprintf, dopr) that are now done, in > addition to pretty much the same work as before (i.e. sprintf("%.*f")).
I'm *NOT* proposing that as the actual solution, but as a datapoint, it might be interesting that hardcoding the precision and thus allowing use ofusing strfromd() instead of sprintf yields a *better* runtime than master. Time: 10255.134 ms (00:10.255) Greetings, Andres Freund
