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

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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.
This commit is contained in:
konstantin@mysql.com
2006-04-07 23:37:06 +04:00
parent 3c93e6efa5
commit 518993312c
9 changed files with 464 additions and 60 deletions
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28
sql/sql_class.h
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@@ -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();