Re: Performance improvements for src/port/snprintf.c

On 2018-09-12 14:14:15 -0400, Tom Lane wrote:
> Alexander Kuzmenkov <a.kuzmenkov@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")).

- Andres