Re: remaining sql/json patches - Mailing list pgsql-hackers

On Thu, Nov 16, 2023 at 2:11 AM Andres Freund <andres@anarazel.de> wrote:

On 2023-11-15 22:00:41 +0900, Amit Langote wrote:

This causes a nontrivial increase in the size of the parser (~5% in an
optimized build here), I wonder if we can do better.

Hmm, sorry if I sound ignorant but what do you mean by the parser here?

gram.o, in an optimized build.

I can see that the byte-size of gram.o increases by 1.66% after the
above additions  (1.72% with previous versions).

I'm not sure anymore how I measured it, but if you just looked at the total
file size, that might not show the full gain, because of debug symbols
etc. You can use the size command to look at just the code and data size.

$ size /tmp/gram.*
  text    data     bss     dec     hex filename
661808       0       0  661808   a1930 /tmp/gram.o.unpatched
672800       0       0  672800   a4420 /tmp/gram.o.patched

That's still a 1.66% increase in the code size:

(672800 - 661808) / 661808 % = 1.66

As for gram.c, the increase is a bit larger:

$ ll /tmp/gram.*
-rw-rw-r--. 1 amit amit 2605925 Nov 16 16:18 /tmp/gram.c.unpatched
-rw-rw-r--. 1 amit amit 2709422 Nov 16 16:22 /tmp/gram.c.patched

(2709422 - 2605925) / 2605925 % = 3.97

I've also checked
using log_parser_stats that there isn't much slowdown in the
raw-parsing speed.

What does "isn't much slowdown" mean in numbers?

Sure, the benchmark I used measured the elapsed time (using
log_parser_stats) of parsing a simple select statement (*) averaged
over 10000 repetitions of the same query performed with `psql -c`:

Unpatched: 0.000061 seconds
Patched: 0.000061 seconds

Here's a look at the perf:

Unpatched:
  0.59%  [.] AllocSetAlloc
  0.51%  [.] hash_search_with_hash_value
  0.47%  [.] base_yyparse

Patched:
  0.63%  [.] AllocSetAlloc
  0.52%  [.] hash_search_with_hash_value
  0.44%  [.] base_yyparse

(*) select 1, 2, 3 from foo where a = 1

Is there a more relevant benchmark I could use?