From: Nathan Bossart <nathandbossart@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Joe Conway <mail@joeconway.com>
Cc: Andrew Dunstan <andrew@dunslane.net>
Cc: Davin Shearer <davin@apache.org>
Cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: Emitting JSON to file using COPY TO
Date: Wed, 6 Dec 2023 20:56:22 -0600
Message-ID: <20231207025622.GA3011676@nathanxps13> (raw)
In-Reply-To: <1136975.1701894046@sss.pgh.pa.us>
References: <7a60faf6-e7f1-419d-aee6-10a78ea2fe81@joeconway.com>
<2e7ff718-895d-83fc-46f7-be25e23b23b4@dunslane.net>
<!bbf922c5-f571-483e-a2c6-2730b02183fe@joeconway.com>
<1104915.1701877459@sss.pgh.pa.us>
<19a5f9d8-bd1f-9!e51-0f5b-510c1189a8a7@dunslane.net>
<1110690.1701880139@sss.pgh.pa.us>
<20231206163349.GA2873889@nathanxps13>
<20231206164439.GC2873889@nathanxps13>
<77312d02-9325-4f14-9fe0-2746c2ee12bc@joeconway.com>
<1136975.1701894046@sss.pgh.pa.us>
On Wed, Dec 06, 2023 at 03:20:46PM -0500, Tom Lane wrote:
> If Nathan's perf results hold up elsewhere, it seems like some
> micro-optimization around the text-pushing (appendStringInfoString)
> might be more useful than caching. The 7% spent in cache lookups
> could be worth going after later, but it's not the top of the list.
Hah, it turns out my benchmark of 110M integers really stresses the
JSONTYPE_NUMERIC path in datum_to_json_internal(). That particular path
calls strlen() twice: once for IsValidJsonNumber(), and once in
appendStringInfoString(). If I save the result from IsValidJsonNumber()
and give it to appendBinaryStringInfo() instead, the COPY goes ~8% faster.
It's probably worth giving datum_to_json_internal() a closer look in a new
thread.
diff --git a/src/backend/utils/adt/json.c b/src/backend/utils/adt/json.cindex 71ae53ff97..1951e93d9d 100644--- a/src/backend/utils/adt/json.c+++ b/src/backend/utils/adt/json.c@@ -180,6 +180,7 @@ datum_to_json_internal(Datum val, bool is_null, StringInfo result,
{
char *outputstr;
text *jsontext;
+ int len;
check_stack_depth();
@@ -223,8 +224,8 @@ datum_to_json_internal(Datum val, bool is_null, StringInfo result,
* Don't call escape_json for a non-key if it's a valid JSON
* number.
*/
- if (!key_scalar && IsValidJsonNumber(outputstr, strlen(outputstr)))- appendStringInfoString(result, outputstr);+ if (!key_scalar && IsValidJsonNumber(outputstr, (len = strlen(outputstr))))+ appendBinaryStringInfo(result, outputstr, len);
else
escape_json(result, outputstr);
pfree(outputstr);
--
Nathan Bossart
Amazon Web Services: https://aws.amazon.com
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Subject: Re: Emitting JSON to file using COPY TO
In-Reply-To: <20231207025622.GA3011676@nathanxps13>
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