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Followup to Bug#45225 Locking: hang if drop table with no timeout

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This patch prevents system threads and system table accesses from
using user-specified values for "lock_wait_timeout". Instead all
such accesses are done using the default value (1 year).

This prevents background tasks (such as replication, events, 
accessing stored function definitions, logging, reading time-zone
information, etc.) from failing in cases where the global value
of "lock_wait_timeout" is set very low.

The patch also simplifies the open tables API. Rather than adding
another convenience function for opening and locking system tables,
this patch removes most of the existing convenience functions for
open_and_lock_tables_derived(). Before, open_and_lock_tables() was
a convenience function that enforced derived tables handling, while
open_and_lock_tables_derived() was the main function where derived
tables handling was optional. Now, this convencience function is
gone and the main function is renamed to open_and_lock_tables(). 

No test case added as it would have required the use of --sleep to
check that system threads and system tables have a different timeout
value from the user-specified "lock_wait_timeout" system variable.
This commit is contained in:
Jon Olav Hauglid
2010-02-24 18:04:00 +01:00
parent b6e0f92f05
commit dd42aab840
24 changed files with 128 additions and 114 deletions
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12
sql/sql_class.h
View File

@ -1280,7 +1280,7 @@ public:
OT_DISCOVER,
OT_REPAIR
};
Open_table_context(THD *thd);
Open_table_context(THD *thd, ulong timeout);
bool recover_from_failed_open(THD *thd, MDL_request *mdl_request,
TABLE_LIST *table);
@ -1305,6 +1305,11 @@ public:
MDL_request *get_global_mdl_request(THD *thd);
inline ulong get_timeout() const
{
return m_timeout;
}
private:
/** List of requests for all locks taken so far. Used for waiting on locks. */
MDL_request_list m_mdl_requests;
@ -1322,6 +1327,11 @@ private:
opening tables for statements which take upgradable shared metadata locks.
*/
MDL_request *m_global_mdl_request;
/**
Lock timeout in seconds. Initialized to LONG_TIMEOUT when opening system
tables or to the "lock_wait_timeout" system variable for regular tables.
*/
uint m_timeout;
};