A fix and a test case for Bug#16365 "Prepared Statements: DoS with

too many open statements". The patch adds a new global variable
@@max_prepared_stmt_count. This variable limits the total number
of prepared statements in the server. The default value of
@@max_prepared_stmt_count is 16382. 16382 small statements
(a select against 3 tables with GROUP, ORDER and LIMIT) consume 
100MB of RAM. Once this limit has been reached, the server will 
refuse to prepare a new statement and return ER_UNKNOWN_ERROR 
(unfortunately, we can't add new errors to 4.1 without breaking 5.0). The limit is changeable after startup
and can accept any value from 0 to 1 million. In case
the new value of the limit is less than the current
statement count, no new statements can be added, while the old
still can be used. Additionally, the current count of prepared 
statements is now available through a global read-only variable 
@@prepared_stmt_count.


mysql-test/r/ps.result:
  Test results fixed (a test case for Bug#16365)
mysql-test/t/ps.test:
  A test case for Bug#16365 "Prepared Statements: DoS with too many 
  open statements". Also fix statement leaks in other tests.
sql/mysql_priv.h:
  Add declarations for new global variables.
sql/mysqld.cc:
  Add definitions of max_prepared_stmt_count, prepared_stmt_count.
sql/set_var.cc:
  Implement support for @@prepared_stmt_count and 
  @@max_prepared_stmt_count. Currently these variables are queried
  without acquiring LOCK_prepared_stmt_count due to limitations of
  the set_var/sys_var class design. Updates are, however, protected 
  with a lock.
sql/set_var.h:
  New declarations to add support for @@max_prepared_stmt_count.
  Implement a new class, where the lock to be used when updating
  a variable is a parameter.
sql/sql_class.cc:
  Add accounting of the total number of prepared statements in the
  server to the methods of Statement_map.
sql/sql_class.h:
  Add accounting of the total number of prepared statements in the
  server to the methods of Statement_map.
sql/sql_prepare.cc:
  Statement_map::insert will now send a message in case of an
  error.

1 files changed, 5 insertions, 23 deletions

diff --git a/sql/sql_class.h b/sql/sql_class.h
index 41170192892..8fe1e7990e9 100644
--- a/sql/sql_class.h
+++ b/sql/sql_class.h
@@ -620,7 +620,7 @@ class Statement_map
 public:
   Statement_map();
 
-  int insert(Statement *statement);
+  int insert(THD *thd, Statement *statement);
 
   Statement *find_by_name(LEX_STRING *name)
   {
@@ -642,29 +642,10 @@ public:
     }
     return last_found_statement;
   }
-  void erase(Statement *statement)
-  {
-    if (statement == last_found_statement)
-      last_found_statement= 0;
-    if (statement->name.str)
-    {
-      hash_delete(&names_hash, (byte *) statement);  
-    }
-    hash_delete(&st_hash, (byte *) statement);
-  }
+  void erase(Statement *statement);
   /* Erase all statements (calls Statement destructor) */
-  void reset()
-  {
-    my_hash_reset(&names_hash);
-    my_hash_reset(&st_hash);
-    last_found_statement= 0;
-  }
-
-  ~Statement_map()
-  {
-    hash_free(&names_hash);
-    hash_free(&st_hash);
-  }
+  void reset();
+  ~Statement_map();
 private:
   HASH st_hash;
   HASH names_hash;
@@ -932,6 +913,7 @@ public:
   {
     my_bool my_bool_value;
     long    long_value;
+    ulong   ulong_value;
   } sys_var_tmp;
 
   THD();