Subject: [PATCH v3] Cleanup explicit PREPARE query strings

From: Julien Rouhaud <[email-masked]>
Date: Wed, 24 Dec 2025 22:31:52 +0800

When a multi statements query string contains one PREPARE statement (or
multiple), the whole query string was saved in the cached plan.  This is
wasteful as that string can be artitrarily big, but it can also confusing as
some other parts like pg_prepared_statements will output the saved query string
as-is.

This commit changes this behavior and only stores the part of the query string
that correspond to any given PREPARED statement, similarly to how it's already
done in pg_stat_statements.
---
 contrib/auto_explain/t/001_auto_explain.pl    |  8 +--
 contrib/pg_stat_statements/Makefile           |  1 +
 .../pg_stat_statements/expected/prepare.out   | 53 +++++++++++++++++++
 contrib/pg_stat_statements/meson.build        |  1 +
 contrib/pg_stat_statements/sql/prepare.sql    | 15 ++++++
 src/backend/commands/prepare.c                | 45 ++++++++++++++--
 src/test/regress/expected/prepare.out         | 44 +++++++++------
 src/test/regress/sql/prepare.sql              |  2 +-
 8 files changed, 143 insertions(+), 26 deletions(-)
 create mode 100644 contrib/pg_stat_statements/expected/prepare.out
 create mode 100644 contrib/pg_stat_statements/sql/prepare.sql

diff --git a/contrib/auto_explain/t/001_auto_explain.pl b/contrib/auto_explain/t/001_auto_explain.pl
index 5f673bd14c1..f2d8625f8bb 100644
--- a/contrib/auto_explain/t/001_auto_explain.pl
+++ b/contrib/auto_explain/t/001_auto_explain.pl
@@ -60,7 +60,7 @@ $log_contents = query_log($node,
 
 like(
 	$log_contents,
-	qr/Query Text: PREPARE get_proc\(name\) AS SELECT \* FROM pg_proc WHERE proname = \$1;/,
+	qr/Query Text: PREPARE get_proc\(name\) AS SELECT \* FROM pg_proc WHERE proname = \$1/,
 	"prepared query text logged, text mode");
 
 like(
@@ -82,7 +82,7 @@ $log_contents = query_log(
 
 like(
 	$log_contents,
-	qr/Query Text: PREPARE get_type\(name\) AS SELECT \* FROM pg_type WHERE typname = \$1;/,
+	qr/Query Text: PREPARE get_type\(name\) AS SELECT \* FROM pg_type WHERE typname = \$1/,
 	"prepared query text logged, text mode");
 
 like(
@@ -98,7 +98,7 @@ $log_contents = query_log(
 
 like(
 	$log_contents,
-	qr/Query Text: PREPARE get_type\(name\) AS SELECT \* FROM pg_type WHERE typname = \$1;/,
+	qr/Query Text: PREPARE get_type\(name\) AS SELECT \* FROM pg_type WHERE typname = \$1/,
 	"prepared query text logged, text mode");
 
 unlike(
@@ -164,7 +164,7 @@ $log_contents = query_log(
 
 like(
 	$log_contents,
-	qr/"Query Text": "PREPARE get_class\(name\) AS SELECT \* FROM pg_class WHERE relname = \$1;"/,
+	qr/"Query Text": "PREPARE get_class\(name\) AS SELECT \* FROM pg_class WHERE relname = \$1"/,
 	"prepared query text logged, json mode");
 
 like(
diff --git a/contrib/pg_stat_statements/Makefile b/contrib/pg_stat_statements/Makefile
index c27e9529bb6..ac967687796 100644
--- a/contrib/pg_stat_statements/Makefile
+++ b/contrib/pg_stat_statements/Makefile
@@ -36,6 +36,7 @@ REGRESS = \
 	parallel \
 	plancache \
 	squashing \
+	prepare \
 	cleanup \
 	oldextversions
 
diff --git a/contrib/pg_stat_statements/expected/prepare.out b/contrib/pg_stat_statements/expected/prepare.out
new file mode 100644
index 00000000000..010e289c1b0
--- /dev/null
+++ b/contrib/pg_stat_statements/expected/prepare.out
@@ -0,0 +1,53 @@
+-- Tests for PREPARE
+SELECT pg_stat_statements_reset() IS NOT NULL AS t;
+ t 
+---
+ t
+(1 row)
+
+-- Test that prepared statements in a multi-query string behaves as expected
+SELECT 1\;PREPARE p1 AS SELECT 1\; PREPARE p2(int) AS SELECT 2 * $1\; SELECT 1, 1;
+ ?column? 
+----------
+        1
+(1 row)
+
+ ?column? | ?column? 
+----------+----------
+        1 |        1
+(1 row)
+
+SELECT calls, rows, query FROM pg_stat_statements ORDER BY query COLLATE "C";
+ calls | rows |                       query                        
+-------+------+----------------------------------------------------
+     1 |    1 | SELECT $1
+     1 |    1 | SELECT $1, $2
+     1 |    1 | SELECT pg_stat_statements_reset() IS NOT NULL AS t
+(3 rows)
+
+SELECT pg_stat_statements_reset() IS NOT NULL AS t;
+ t 
+---
+ t
+(1 row)
+
+EXECUTE p1;
+ ?column? 
+----------
+        1
+(1 row)
+
+EXECUTE p2(0);
+ ?column? 
+----------
+        0
+(1 row)
+
+SELECT calls, rows, query FROM pg_stat_statements ORDER BY query COLLATE "C";
+ calls | rows |                       query                        
+-------+------+----------------------------------------------------
+     1 |    1 | PREPARE p1 AS SELECT 1
+     1 |    1 | PREPARE p2(int) AS SELECT 2 * $1
+     1 |    1 | SELECT pg_stat_statements_reset() IS NOT NULL AS t
+(3 rows)
+
diff --git a/contrib/pg_stat_statements/meson.build b/contrib/pg_stat_statements/meson.build
index 9d78cb88b7d..c9e1d446d39 100644
--- a/contrib/pg_stat_statements/meson.build
+++ b/contrib/pg_stat_statements/meson.build
@@ -58,6 +58,7 @@ tests += {
       'parallel',
       'plancache',
       'squashing',
+      'prepare',
       'cleanup',
       'oldextversions',
     ],
diff --git a/contrib/pg_stat_statements/sql/prepare.sql b/contrib/pg_stat_statements/sql/prepare.sql
new file mode 100644
index 00000000000..a6bc5de4430
--- /dev/null
+++ b/contrib/pg_stat_statements/sql/prepare.sql
@@ -0,0 +1,15 @@
+-- Tests for PREPARE
+
+SELECT pg_stat_statements_reset() IS NOT NULL AS t;
+
+-- Test that prepared statements in a multi-query string behaves as expected
+SELECT 1\;PREPARE p1 AS SELECT 1\; PREPARE p2(int) AS SELECT 2 * $1\; SELECT 1, 1;
+
+SELECT calls, rows, query FROM pg_stat_statements ORDER BY query COLLATE "C";
+
+SELECT pg_stat_statements_reset() IS NOT NULL AS t;
+
+EXECUTE p1;
+EXECUTE p2(0);
+
+SELECT calls, rows, query FROM pg_stat_statements ORDER BY query COLLATE "C";
diff --git a/src/backend/commands/prepare.c b/src/backend/commands/prepare.c
index 5b86a727587..b8fe3dd5302 100644
--- a/src/backend/commands/prepare.c
+++ b/src/backend/commands/prepare.c
@@ -27,6 +27,7 @@
 #include "commands/prepare.h"
 #include "funcapi.h"
 #include "nodes/nodeFuncs.h"
+#include "nodes/queryjumble.h"
 #include "parser/parse_coerce.h"
 #include "parser/parse_collate.h"
 #include "parser/parse_expr.h"
@@ -64,6 +65,7 @@ PrepareQuery(ParseState *pstate, PrepareStmt *stmt,
 	Oid		   *argtypes = NULL;
 	int			nargs;
 	List	   *query_list;
+	const char *new_query;
 
 	/*
 	 * Disallow empty-string statement name (conflicts with protocol-level
@@ -80,14 +82,49 @@ PrepareQuery(ParseState *pstate, PrepareStmt *stmt,
 	 */
 	rawstmt = makeNode(RawStmt);
 	rawstmt->stmt = stmt->query;
-	rawstmt->stmt_location = stmt_location;
-	rawstmt->stmt_len = stmt_len;
+
+	/*
+	 * Extract the query text if possible.
+	 *
+	 * If we have a statement location, we can extract the relevant part of the
+	 * possibly multi-statement query string.  If not just use what we were
+	 * given.
+	 */
+	if (stmt_location < 0)
+	{
+		rawstmt->stmt_location = stmt_location;
+		rawstmt->stmt_len = stmt_len;
+		new_query = pstate->p_sourcetext;
+	}
+	else
+	{
+		const char *cleaned;
+		char	   *tmp;
+
+		rawstmt->stmt_len = stmt_len;
+		cleaned = CleanQuerytext(pstate->p_sourcetext, &stmt_location,
+								 &rawstmt->stmt_len);
+
+		if (rawstmt->stmt_len == 0)
+			rawstmt->stmt_len = strlen(cleaned);
+
+		/*
+		 * CleanQuerytext() removes any leading whitespace and returns a
+		 * pointer to the first actual character, so the cleaned query string
+		 * is guaranteed to start at offset 0.
+		 */
+		rawstmt->stmt_location = 0;
+		tmp = palloc(rawstmt->stmt_len + 1);
+		strlcpy(tmp, cleaned, rawstmt->stmt_len + 1);
+
+		new_query = tmp;
+	}
 
 	/*
 	 * Create the CachedPlanSource before we do parse analysis, since it needs
 	 * to see the unmodified raw parse tree.
 	 */
-	plansource = CreateCachedPlan(rawstmt, pstate->p_sourcetext,
+	plansource = CreateCachedPlan(rawstmt, new_query,
 								  CreateCommandTag(stmt->query));
 
 	/* Transform list of TypeNames to array of type OIDs */
@@ -116,7 +153,7 @@ PrepareQuery(ParseState *pstate, PrepareStmt *stmt,
 	 * information about unknown parameters to be deduced from context.
 	 * Rewrite the query. The result could be 0, 1, or many queries.
 	 */
-	query_list = pg_analyze_and_rewrite_varparams(rawstmt, pstate->p_sourcetext,
+	query_list = pg_analyze_and_rewrite_varparams(rawstmt, new_query,
 												  &argtypes, &nargs, NULL);
 
 	/* Finish filling in the CachedPlanSource */
diff --git a/src/test/regress/expected/prepare.out b/src/test/regress/expected/prepare.out
index 5815e17b39c..c645a4e5d0e 100644
--- a/src/test/regress/expected/prepare.out
+++ b/src/test/regress/expected/prepare.out
@@ -6,7 +6,17 @@ SELECT name, statement, parameter_types, result_types FROM pg_prepared_statement
 ------+-----------+-----------------+--------------
 (0 rows)
 
-PREPARE q1 AS SELECT 1 AS a;
+SELECT 'bingo'\;  PREPARE q1 AS SELECT 1 AS a \; SELECT 42;
+ ?column? 
+----------
+ bingo
+(1 row)
+
+ ?column? 
+----------
+       42
+(1 row)
+
 EXECUTE q1;
  a 
 ---
@@ -14,9 +24,9 @@ EXECUTE q1;
 (1 row)
 
 SELECT name, statement, parameter_types, result_types FROM pg_prepared_statements;
- name |          statement           | parameter_types | result_types 
-------+------------------------------+-----------------+--------------
- q1   | PREPARE q1 AS SELECT 1 AS a; | {}              | {integer}
+ name |          statement          | parameter_types | result_types 
+------+-----------------------------+-----------------+--------------
+ q1   | PREPARE q1 AS SELECT 1 AS a | {}              | {integer}
 (1 row)
 
 -- should fail
@@ -33,18 +43,18 @@ EXECUTE q1;
 
 PREPARE q2 AS SELECT 2 AS b;
 SELECT name, statement, parameter_types, result_types FROM pg_prepared_statements;
- name |          statement           | parameter_types | result_types 
-------+------------------------------+-----------------+--------------
- q1   | PREPARE q1 AS SELECT 2;      | {}              | {integer}
- q2   | PREPARE q2 AS SELECT 2 AS b; | {}              | {integer}
+ name |          statement          | parameter_types | result_types 
+------+-----------------------------+-----------------+--------------
+ q1   | PREPARE q1 AS SELECT 2      | {}              | {integer}
+ q2   | PREPARE q2 AS SELECT 2 AS b | {}              | {integer}
 (2 rows)
 
 -- sql92 syntax
 DEALLOCATE PREPARE q1;
 SELECT name, statement, parameter_types, result_types FROM pg_prepared_statements;
- name |          statement           | parameter_types | result_types 
-------+------------------------------+-----------------+--------------
- q2   | PREPARE q2 AS SELECT 2 AS b; | {}              | {integer}
+ name |          statement          | parameter_types | result_types 
+------+-----------------------------+-----------------+--------------
+ q2   | PREPARE q2 AS SELECT 2 AS b | {}              | {integer}
 (1 row)
 
 DEALLOCATE PREPARE q2;
@@ -168,20 +178,20 @@ SELECT name, statement, parameter_types, result_types FROM pg_prepared_statement
 ------+------------------------------------------------------------------+----------------------------------------------------+--------------------------------------------------------------------------------------------------------------------------
  q2   | PREPARE q2(text) AS                                             +| {text}                                             | {name,boolean,boolean}
       |         SELECT datname, datistemplate, datallowconn             +|                                                    | 
-      |         FROM pg_database WHERE datname = $1;                     |                                                    | 
+      |         FROM pg_database WHERE datname = $1                      |                                                    | 
  q3   | PREPARE q3(text, int, float, boolean, smallint) AS              +| {text,integer,"double precision",boolean,smallint} | {integer,integer,integer,integer,integer,integer,integer,integer,integer,integer,integer,integer,integer,name,name,name}
       |         SELECT * FROM tenk1 WHERE string4 = $1 AND (four = $2 OR+|                                                    | 
       |         ten = $3::bigint OR true = $4 OR odd = $5::int)         +|                                                    | 
-      |         ORDER BY unique1;                                        |                                                    | 
+      |         ORDER BY unique1                                         |                                                    | 
  q5   | PREPARE q5(int, text) AS                                        +| {integer,text}                                     | {integer,integer,integer,integer,integer,integer,integer,integer,integer,integer,integer,integer,integer,name,name,name}
       |         SELECT * FROM tenk1 WHERE unique1 = $1 OR stringu1 = $2 +|                                                    | 
-      |         ORDER BY unique1;                                        |                                                    | 
+      |         ORDER BY unique1                                         |                                                    | 
  q6   | PREPARE q6 AS                                                   +| {integer,name}                                     | {integer,integer,integer,integer,integer,integer,integer,integer,integer,integer,integer,integer,integer,name,name,name}
-      |     SELECT * FROM tenk1 WHERE unique1 = $1 AND stringu1 = $2;    |                                                    | 
+      |     SELECT * FROM tenk1 WHERE unique1 = $1 AND stringu1 = $2     |                                                    | 
  q7   | PREPARE q7(unknown) AS                                          +| {path}                                             | {text,path}
-      |     SELECT * FROM road WHERE thepath = $1;                       |                                                    | 
+      |     SELECT * FROM road WHERE thepath = $1                        |                                                    | 
  q8   | PREPARE q8 AS                                                   +| {integer,name}                                     | 
-      |     UPDATE tenk1 SET stringu1 = $2 WHERE unique1 = $1;           |                                                    | 
+      |     UPDATE tenk1 SET stringu1 = $2 WHERE unique1 = $1            |                                                    | 
 (6 rows)
 
 -- test DEALLOCATE ALL;
diff --git a/src/test/regress/sql/prepare.sql b/src/test/regress/sql/prepare.sql
index c6098dc95ce..0e7fe44725e 100644
--- a/src/test/regress/sql/prepare.sql
+++ b/src/test/regress/sql/prepare.sql
@@ -4,7 +4,7 @@
 
 SELECT name, statement, parameter_types, result_types FROM pg_prepared_statements;
 
-PREPARE q1 AS SELECT 1 AS a;
+SELECT 'bingo'\;  PREPARE q1 AS SELECT 1 AS a \; SELECT 42;
 EXECUTE q1;
 
 SELECT name, statement, parameter_types, result_types FROM pg_prepared_statements;
-- 
2.52.0

--xBRJzsblsXcilRYX--