BUG#9953: CONVERT_TZ requires mysql.time_zone_name to be locked

The problem was that some facilities (like CONVERT_TZ() function or
server HELP statement) may require implicit access to some tables in
'mysql' database.  This access was done by ordinary means of adding
such tables to the list of tables the query is going to open.
However, if we issued LOCK TABLES before that, we would get "table
was not locked" error trying to open such implicit tables.

The solution is to treat certain tables as MySQL system tables, like
we already do for mysql.proc.  Such tables may be opened for reading
at any moment regardless of any locks in effect.  The cost of this is
that system table may be locked for writing only together with other
system tables, it is disallowed to lock system tables for writing and
have any other lock on any other table.

After this patch the following tables are treated as MySQL system
tables:
  mysql.help_category
  mysql.help_keyword
  mysql.help_relation
  mysql.help_topic
  mysql.proc (it already was)
  mysql.time_zone
  mysql.time_zone_leap_second
  mysql.time_zone_name
  mysql.time_zone_transition
  mysql.time_zone_transition_type

These tables are now opened with open_system_tables_for_read() and
closed with close_system_tables(), or one table may be opened with
open_system_table_for_update() and closed with close_thread_tables()
(the latter is used for mysql.proc table, which is updated as part of
normal MySQL server operation).  These functions may be used when
some tables were opened and locked already.

NOTE: online update of time zone tables is not possible during
replication, because there's no time zone cache flush neither on LOCK
TABLES, nor on FLUSH TABLES, so the master may serve stale time zone
data from cache, while on slave updated data will be loaded from the
time zone tables.

1 files changed, 0 insertions, 6 deletions

diff --git a/sql/sql_lex.h b/sql/sql_lex.h
index 68399b188a1..f797d08b034 100644
--- a/sql/sql_lex.h
+++ b/sql/sql_lex.h
@@ -1086,11 +1086,6 @@ typedef struct st_lex : public Query_tables_list
   bool prepared_stmt_code_is_varref;
   /* Names of user variables holding parameters (in EXECUTE) */
   List<LEX_STRING> prepared_stmt_params;
-  /*
-    Points to part of global table list which contains time zone tables
-    implicitly used by the statement.
-  */
-  TABLE_LIST *time_zone_tables_used;
   sp_head *sphead;
   sp_name *spname;
   bool sp_lex_in_use;	/* Keep track on lex usage in SPs for error handling */
@@ -1177,7 +1172,6 @@ typedef struct st_lex : public Query_tables_list
   TABLE_LIST *unlink_first_table(bool *link_to_local);
   void link_first_table_back(TABLE_LIST *first, bool link_to_local);
   void first_lists_tables_same();
-  bool add_time_zone_tables_to_query_tables(THD *thd);
 
   bool can_be_merged();
   bool can_use_merged();