Horton

Re: micro-optimizing json.c

Jeff Davis <pgsql@j-davis.com>

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From: Jeff Davis <pgsql@j-davis.com>
To: Nathan Bossart <nathandbossart@gmail.com>, Joe Conway <mail@joeconway.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Andrew Dunstan <andrew@dunslane.net>, Davin Shearer <davin@apache.org>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2023-12-07T23:43:47Z
Lists: pgsql-hackers 
On Thu, 2023-12-07 at 17:12 -0600, Nathan Bossart wrote:
> Here's a patch that removes a couple of strlen() calls that showed up
> prominently in perf for a COPY TO (FORMAT json) on 110M integers.  On
> my
> laptop, I see a 20% speedup from ~23.6s to ~18.9s for this test.

Nice improvement. The use of (len = ...) in a conditional is slightly
out of the ordinary, but it makes the conditionals a bit simpler and
you have a comment, so it's fine with me.

I wonder, if there were an efficient cast from numeric to text, then
perhaps you could avoid the strlen() entirely? Maybe there's a way to
use a static buffer to even avoid the palloc() in get_str_from_var()?
Not sure these are worth the effort; just brainstorming.

In any case, +1 to your simple change.

Regards,
	Jeff Davis

Commits

  1. Micro-optimize datum_to_json_internal() some more.

  2. Micro-optimize JSONTYPE_NUMERIC code path in json.c.