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From: Nathan Bossart <[email protected]>
To: Tom Lane <[email protected]>
Cc: Joe Conway <[email protected]>
Cc: Andrew Dunstan <[email protected]>
Cc: Davin Shearer <[email protected]>
Cc: PostgreSQL-development <[email protected]>
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: <[email protected]>
References: <[email protected]>
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	<20231206163349.GA2873889@nathanxps13>
	<20231206164439.GC2873889@nathanxps13>
	<[email protected]>
	<[email protected]>

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.c
index 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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