Wrong behavior about max prepared stmt

[xuyifangreeneyes]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

ref #39736

create table t1
(
  a int primary key,
  b char(10)
);

prepare stmt4 from 'update t1 set a=? where b=?';
set @arg1=55, @arg2='five';
execute stmt4 using @arg1, @arg2;

prepare stmt4 from 'create table t2 (a int)';
execute stmt4;
deallocate prepare stmt4;

set global max_prepared_stmt_count=1;
prepare stmt from "select 1";

2. What did you expect to see? (Required)

mysql> create table t1
    -> (
    ->   a int primary key,
    ->   b char(10)
    -> );
Query OK, 0 rows affected (0.16 sec)

mysql> prepare stmt4 from 'update t1 set a=? where b=?';
Query OK, 0 rows affected (0.01 sec)
Statement prepared

mysql> set @arg1=55, @arg2='five';
Query OK, 0 rows affected (0.01 sec)

mysql> execute stmt4 using @arg1, @arg2;
Query OK, 0 rows affected (0.01 sec)
Rows matched: 0  Changed: 0  Warnings: 0

mysql> prepare stmt4 from 'create table t2 (a int)';
Query OK, 0 rows affected (0.01 sec)
Statement prepared

mysql> execute stmt4;
Query OK, 0 rows affected (0.02 sec)

mysql> deallocate prepare stmt4;
Query OK, 0 rows affected (0.00 sec)

mysql> set global max_prepared_stmt_count=1;
Query OK, 0 rows affected (0.00 sec)

mysql> prepare stmt from "select 1";
Query OK, 0 rows affected (0.00 sec)
Statement prepared

3. What did you see instead (Required)

mysql> create table t1
    -> (
    ->   a int primary key,
    ->   b char(10)
    -> );
Query OK, 0 rows affected (0.07 sec)

mysql> prepare stmt4 from 'update t1 set a=? where b=?';
Query OK, 0 rows affected (0.00 sec)

mysql> set @arg1=55, @arg2='five';
Query OK, 0 rows affected (0.00 sec)

mysql> execute stmt4 using @arg1, @arg2;
Query OK, 0 rows affected (0.02 sec)
Rows matched: 0  Changed: 0  Warnings: 0

mysql> prepare stmt4 from 'create table t2 (a int)';
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> execute stmt4;
Query OK, 0 rows affected (0.02 sec)

mysql> deallocate prepare stmt4;
Query OK, 0 rows affected (0.00 sec)

mysql> set global max_prepared_stmt_count=1;
Query OK, 0 rows affected (0.01 sec)

mysql> prepare stmt from "select 1";
ERROR 1461 (42000): Can't create more than maxPreparedStmtCount statements (current value: 1)

4. What is your TiDB version? (Required)

#39736

[qw4990]

In the internal of TiDB, each prepared statement has a unique ID, and TiDB uses these ID to count how many statements there.
So if we run 2 prepare statements with the same statement name twice, TiDB will create 2 different prepared statements internally, and the count becomes to 2.