From 0de9e40f4b167dfb1d600b362f8cf469e992cec7 Mon Sep 17 00:00:00 2001
From: Monty <monty@mariadb.org>
Date: Mon, 21 Oct 2024 15:05:14 +0300
Subject: [PATCH] Added status variable "stack_usable" to be able to check
 stack usage

---
 mysql-test/main/stack.result | 46 +++++++++++++++++++++++++++
 mysql-test/main/stack.test   | 60 ++++++++++++++++++++++++++++++++++++
 sql/mysqld.cc                | 16 ++++++++++
 3 files changed, 122 insertions(+)
 create mode 100644 mysql-test/main/stack.result
 create mode 100644 mysql-test/main/stack.test

diff --git a/mysql-test/main/stack.result b/mysql-test/main/stack.result
new file mode 100644
index 00000000000..a1f82a66104
--- /dev/null
+++ b/mysql-test/main/stack.result
@@ -0,0 +1,46 @@
+# Checking stack usage
+#
+# basic tests
+#
+select variable_value > 0 from information_schema.session_status where variable_name="stack_usage";
+variable_value > 0
+1
+#
+# Ensure stack usage is same for each iteration when using WITH recursive
+#
+create table t1
+WITH recursive Fibonacci(PrevN, N, Stack) AS
+(
+SELECT 0, 1, 0
+UNION ALL
+SELECT N, PrevN + N, (select variable_value from information_schema.session_status where variable_name="stack_usage")
+FROM Fibonacci
+WHERE N < 100000
+)
+SELECT PrevN as N, Stack FROM Fibonacci;
+select (select stack from t1 where n=2) = (select stack from t1 where N=75025);
+(select stack from t1 where n=2) = (select stack from t1 where N=75025)
+1
+DROP table t1;
+#
+# Check stack with recursion
+#
+set @@max_sp_recursion_depth=20;
+create or replace procedure recursion(x int, max int, OUT res int)
+begin
+select variable_value into res from information_schema.session_status where variable_name="stack_usage";
+if (x < max) then
+call recursion(x+1, max, res);
+end if;
+end;
+$$
+call recursion(0,2,@s1);
+call recursion(0,3,@s2);
+call recursion(0,4,@s3);
+select @s1 > 0 && @s2 > 0 && @s3 > 0;
+@s1 > 0 && @s2 > 0 && @s3 > 0
+1
+drop procedure recursion;
+#
+# End of 10.5 tests
+#
diff --git a/mysql-test/main/stack.test b/mysql-test/main/stack.test
new file mode 100644
index 00000000000..d25d4620dec
--- /dev/null
+++ b/mysql-test/main/stack.test
@@ -0,0 +1,60 @@
+--echo # Checking stack usage
+
+--echo #
+--echo # basic tests
+--echo #
+
+select variable_value > 0 from information_schema.session_status where variable_name="stack_usage";
+
+
+--echo #
+--echo # Ensure stack usage is same for each iteration when using WITH recursive
+--echo #
+
+create table t1
+WITH recursive Fibonacci(PrevN, N, Stack) AS
+(
+     SELECT 0, 1, 0
+     UNION ALL
+     SELECT N, PrevN + N, (select variable_value from information_schema.session_status where variable_name="stack_usage")
+     FROM Fibonacci
+     WHERE N < 100000
+)
+SELECT PrevN as N, Stack FROM Fibonacci;
+
+select (select stack from t1 where n=2) = (select stack from t1 where N=75025);
+DROP table t1;
+
+--echo #
+--echo # Check stack with recursion
+--echo #
+
+set @@max_sp_recursion_depth=20;
+delimiter $$;
+create or replace procedure recursion(x int, max int, OUT res int)
+begin
+  select variable_value into res from information_schema.session_status where variable_name="stack_usage";
+  if (x < max) then
+    call recursion(x+1, max, res);
+  end if;
+end;
+$$
+
+delimiter ;$$
+
+call recursion(0,2,@s1);
+call recursion(0,3,@s2);
+call recursion(0,4,@s3);
+
+select @s1 > 0 && @s2 > 0 && @s3 > 0;
+if (`select @s2-@s1 <> @s3 - @s2`)
+{
+  echo "Wrong result";
+  select @s1 ,@s2, @s3, @s2-@s1, @s3-@s2;
+}
+
+drop procedure recursion;
+
+--echo #
+--echo # End of 10.5 tests
+--echo #
diff --git a/sql/mysqld.cc b/sql/mysqld.cc
index f82e8e111c2..7663069e034 100644
--- a/sql/mysqld.cc
+++ b/sql/mysqld.cc
@@ -7315,6 +7315,21 @@ static int show_memory_used(THD *thd, SHOW_VAR *var, void *buff,
 }
 
 
+static int show_stack_usage(THD *thd, SHOW_VAR *var, void *buff,
+                            system_status_var *, enum_var_type scope)
+{
+  var->type= SHOW_ULONGLONG;
+  var->value= buff;
+  // We cannot get stack usage for 'global' or for another thread
+  if (scope == OPT_GLOBAL || thd != current_thd)
+    *(ulonglong*) buff= 0;
+  else
+    *(ulonglong*) buff= (ulonglong) (available_stack_size((char*) thd->thread_stack,
+                                                          my_get_stack_pointer(0)));
+  return 0;
+}
+
+
 #ifndef DBUG_OFF
 static int debug_status_func(THD *thd, SHOW_VAR *var, void *buff,
                              system_status_var *, enum_var_type)
@@ -7581,6 +7596,7 @@ SHOW_VAR status_vars[]= {
   {"Ssl_version",              (char*) &show_ssl_get_version, SHOW_SIMPLE_FUNC},
 #endif
 #endif /* HAVE_OPENSSL */
+  SHOW_FUNC_ENTRY("stack_usage", &show_stack_usage),
   {"Syncs",                    (char*) &my_sync_count,          SHOW_LONG_NOFLUSH},
   /*
     Expression cache used only for caching subqueries now, so its statistic