/*
Enum enum_locked_tables_mode and locked_tables_mode member are
used to indicate whether the so-called "locked tables mode" is on,
and what kind of mode is active.
Locked tables mode is used when it's necessary to open and
lock many tables at once, for usage across multiple
(sub-)statements.
This may be necessary either for queries that use stored functions
and triggers, in which case the statements inside functions and
triggers may be executed many times, or for implementation of
LOCK TABLES, in which case the opened tables are reused by all
subsequent statements until a call to UNLOCK TABLES.
The kind of locked tables mode employed for stored functions and
triggers is also called "prelocked mode".
In this mode, first open_tables() call to open the tables used
in a statement analyses all functions used by the statement
and adds all indirectly used tables to the list of tables to
open and lock.
It also marks the parse tree of the statement as requiring
prelocking. After that, lock_tables() locks the entire list
of tables and changes THD::locked_tables_modeto LTM_PRELOCKED.
All statements executed inside functions or triggers
use the prelocked tables, instead of opening their own ones.
Prelocked mode is turned off automatically once close_thread_tables()
of the main statement is called.
*/
enum enum_locked_tables_mode locked_tables_mode; |
