Improve query denormalization regression test

Add a new test case:

1. Execute a prepared statement with larger execution time first.
2. Execute the same prepared statement with cheap execution time.
3. Ensures that the denormalized heavy query is not replaced by the
   cheaper.

regression/expected/denorm_prepared_statements.out

@@ -7,6 +7,8 @@ SELECT pg_stat_monitor_reset();
  
 (1 row)
 
+-- First test, execute cheap query then heavy query.
+-- Ensure denormalized heavy query replaces the cheaper one.
 PREPARE prepstmt(TEXT, TEXT, TEXT) AS INSERT INTO t1(a, b, c) VALUES($1, $2, $3);
 EXECUTE prepstmt('A', 'B', 'C');
 SELECT SUBSTRING(query, 0, 128), calls FROM pg_stat_monitor ORDER BY query COLLATE "C";
@@ -25,6 +27,32 @@ SELECT SUBSTRING(query, 0, 128), calls FROM pg_stat_monitor ORDER BY query COLLA
  SELECT pg_stat_monitor_reset()                                                                                                  |     1
 (3 rows)
 
+TRUNCATE TABLE t1;
+SELECT pg_stat_monitor_reset();
+ pg_stat_monitor_reset 
+-----------------------
+ 
+(1 row)
+
+-- Second test, execute heavy query then cheap query.
+-- Ensure denormalized heavy query is not replaced by the cheaper one.
+EXECUTE prepstmt(REPEAT('XYZ', 8192), md5(random()::text), REPEAT('RANDOM', 4096));
+SELECT SUBSTRING(query, 0, 128), calls FROM pg_stat_monitor ORDER BY query COLLATE "C";
+                                                            substring                                                            | calls 
+---------------------------------------------------------------------------------------------------------------------------------+-------
+ PREPARE prepstmt(TEXT, TEXT, TEXT) AS INSERT INTO t1(a, b, c) VALUES(XYZXYZXYZXYZXYZXYZXYZXYZXYZXYZXYZXYZXYZXYZXYZXYZXYZXYZXYZX |     1
+ SELECT pg_stat_monitor_reset()                                                                                                  |     1
+(2 rows)
+
+EXECUTE prepstmt('A', 'B', 'C');
+SELECT SUBSTRING(query, 0, 128), calls FROM pg_stat_monitor ORDER BY query COLLATE "C";
+                                                            substring                                                            | calls 
+---------------------------------------------------------------------------------------------------------------------------------+-------
+ PREPARE prepstmt(TEXT, TEXT, TEXT) AS INSERT INTO t1(a, b, c) VALUES(XYZXYZXYZXYZXYZXYZXYZXYZXYZXYZXYZXYZXYZXYZXYZXYZXYZXYZXYZX |     2
+ SELECT SUBSTRING(query, 0, 128), calls FROM pg_stat_monitor ORDER BY query COLLATE "C"                                          |     1
+ SELECT pg_stat_monitor_reset()                                                                                                  |     1
+(3 rows)
+
 DROP TABLE t1;
 SELECT pg_stat_monitor_reset();
  pg_stat_monitor_reset 

regression/sql/denorm_prepared_statements.sql

@@ -5,6 +5,8 @@ CREATE TABLE t1 (a TEXT, b TEXT, c TEXT);
 
 SELECT pg_stat_monitor_reset();
 
+-- First test, execute cheap query then heavy query.
+-- Ensure denormalized heavy query replaces the cheaper one.
 PREPARE prepstmt(TEXT, TEXT, TEXT) AS INSERT INTO t1(a, b, c) VALUES($1, $2, $3);
 
 EXECUTE prepstmt('A', 'B', 'C');
@@ -13,6 +15,18 @@ SELECT SUBSTRING(query, 0, 128), calls FROM pg_stat_monitor ORDER BY query COLLA
 EXECUTE prepstmt(REPEAT('XYZ', 8192), md5(random()::text), REPEAT('RANDOM', 4096));
 SELECT SUBSTRING(query, 0, 128), calls FROM pg_stat_monitor ORDER BY query COLLATE "C";
 
+TRUNCATE TABLE t1;
+SELECT pg_stat_monitor_reset();
+
+-- Second test, execute heavy query then cheap query.
+-- Ensure denormalized heavy query is not replaced by the cheaper one.
+
+EXECUTE prepstmt(REPEAT('XYZ', 8192), md5(random()::text), REPEAT('RANDOM', 4096));
+SELECT SUBSTRING(query, 0, 128), calls FROM pg_stat_monitor ORDER BY query COLLATE "C";
+
+EXECUTE prepstmt('A', 'B', 'C');
+SELECT SUBSTRING(query, 0, 128), calls FROM pg_stat_monitor ORDER BY query COLLATE "C";
+
 DROP TABLE t1;
 
 SELECT pg_stat_monitor_reset();