v3-0001-Don-t-copy-bytea-text-in-convert_from-to-unless-c.patch

From 5eb1f5d9323b8d270411bf156ec065fe7c69b7b8 Mon Sep 17 00:00:00 2001
From: Yurii Rashkovskii <yrashk@gmail.com>
Date: Fri, 24 Nov 2023 06:32:05 -0800
Subject: [PATCH v3] Don't copy bytea/text in convert_from/to unless converted.

`pg_convert` allocates a new bytea whether actual conversion occurred or
not, followed by copying the result which (by definition) is the same as
the original value.

In the case where conversion has not occurred, it will now simply return
the original value, this avoiding unnecessary allocation and copying.
---
 src/backend/utils/mb/mbutils.c | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)
 100.0% src/backend/utils/mb/

diff --git a/src/backend/utils/mb/mbutils.c b/src/backend/utils/mb/mbutils.c
index 67a1ab2ab2..7666d166a5 100644
--- a/src/backend/utils/mb/mbutils.c
+++ b/src/backend/utils/mb/mbutils.c
@@ -585,19 +585,26 @@ pg_convert(PG_FUNCTION_ARGS)
 												  src_encoding,
 												  dest_encoding);
 
-	/* update len if conversion actually happened */
-	if (dest_str != src_str)
-		len = strlen(dest_str);
 
 	/*
-	 * build bytea data type structure.
+	 * If no actual conversion happened, return the original string (we are
+	 * checking pointers to strings instead of encodings because
+	 * pg_do_encoding_conversion() above covers more cases than just encoding
+	 * equality).
 	 */
+	if (dest_str == src_str)
+	{
+		PG_RETURN_BYTEA_P(string);
+	}
+
+	/* if conversion happened, build a new bytea of a correct length */
+	len = strlen(dest_str);
 	retval = (bytea *) palloc(len + VARHDRSZ);
 	SET_VARSIZE(retval, len + VARHDRSZ);
 	memcpy(VARDATA(retval), dest_str, len);
 
-	if (dest_str != src_str)
-		pfree(dest_str);
+	/* free the original result of conversion */
+	pfree(dest_str);
 
 	/* free memory if allocated by the toaster */
 	PG_FREE_IF_COPY(string, 0);
-- 
2.34.1