On Thu, Dec 07, 2023 at 07:40:30PM -0500, Tom Lane wrote:
> Hmm ... I think that might not be the way to think about it. What
> I'm wondering is why we need a test as expensive as IsValidJsonNumber
> in the first place, given that we know this is a numeric data type's
> output. ISTM we only need to reject "Inf"/"-Inf" and "NaN", which
> surely does not require a full parse. Skip over a sign, check for
> "I"/"N", and you're done.
>
> ... and for that matter, why does quoting of Inf/NaN require
> that we apply something as expensive as escape_json? Several other
> paths in this switch have no hesitation about assuming that they
> can just plaster double quotes around what was emitted. How is
> that safe for timestamps but not Inf/NaN?
I did both of these in v2, although I opted to test that the first
character after the optional '-' was a digit instead of testing that it was
_not_ an 'I' or 'N'. I think that should be similar performance-wise, and
maybe it's a bit more future-proof in case someone invents some new
notation for a numeric data type (/shrug). In any case, this seems to
speed up my test by another half a second or so.
I think there are some similar improvements that we can make for
JSONTYPE_BOOL and JSONTYPE_CAST, but I haven't tested them yet.
--
Nathan Bossart
Amazon Web Services: https://aws.amazon.com
>From dc5ec1a2204398fa25390f31771eaa57816a96a1 Mon Sep 17 00:00:00 2001
From: Nathan Bossart <nat...@postgresql.org>
Date: Thu, 7 Dec 2023 16:45:45 -0600
Subject: [PATCH v2 1/1] avoid some strlen() calls in json.c
---
src/backend/utils/adt/json.c | 20 +++++++++++++++-----
1 file changed, 15 insertions(+), 5 deletions(-)
diff --git a/src/backend/utils/adt/json.c b/src/backend/utils/adt/json.c
index cb4311e75f..640d9123ed 100644
--- a/src/backend/utils/adt/json.c
+++ b/src/backend/utils/adt/json.c
@@ -218,13 +218,17 @@ datum_to_json_internal(Datum val, bool is_null, StringInfo result,
outputstr = OidOutputFunctionCall(outfuncoid, val);
/*
- * Don't call escape_json for a non-key if it's a valid JSON
- * number.
+ * Don't quote a non-key if it's a valid JSON number. Since we
+ * know this is a numeric data type's output, we simplify and
+ * open-code the validation for better performance.
*/
- if (!key_scalar && IsValidJsonNumber(outputstr, strlen(outputstr)))
+ if (!key_scalar &&
+ ((*outputstr >= '0' && *outputstr <= '9') ||
+ (*outputstr == '-' &&
+ (outputstr[1] >= '0' && outputstr[1] <= '9'))))
appendStringInfoString(result, outputstr);
else
- escape_json(result, outputstr);
+ appendStringInfo(result, "\"%s\"", outputstr);
pfree(outputstr);
break;
case JSONTYPE_DATE:
@@ -502,8 +506,14 @@ composite_to_json(Datum composite, StringInfo result, bool use_line_feeds)
int i;
bool needsep = false;
const char *sep;
+ int seplen;
+ /*
+ * We can avoid expensive strlen() calls by precalculating the separator
+ * length.
+ */
sep = use_line_feeds ? ",\n " : ",";
+ seplen = use_line_feeds ? sizeof(",\n ") - 1 : sizeof(",") - 1;
td = DatumGetHeapTupleHeader(composite);
@@ -532,7 +542,7 @@ composite_to_json(Datum composite, StringInfo result, bool use_line_feeds)
continue;
if (needsep)
- appendStringInfoString(result, sep);
+ appendBinaryStringInfo(result, sep, seplen);
needsep = true;
attname = NameStr(att->attname);
--
2.25.1
