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, 1 insertions, 34 deletions

diff --git a/sql/tztime.h b/sql/tztime.h
index 248a638074b..b6af4b37468 100644
--- a/sql/tztime.h
+++ b/sql/tztime.h
@@ -59,15 +59,11 @@ public:
 
 extern Time_zone * my_tz_UTC;
 extern Time_zone * my_tz_SYSTEM;
-extern TABLE_LIST * my_tz_get_table_list(THD *thd, TABLE_LIST ***global_next_ptr);
-extern Time_zone * my_tz_find(const String *name, TABLE_LIST *tz_tables);
-extern Time_zone * my_tz_find_with_opening_tz_tables(THD *thd, const String *name);
+extern Time_zone * my_tz_find(THD *thd, const String *name);
 extern my_bool     my_tz_init(THD *org_thd, const char *default_tzname, my_bool bootstrap);
 extern void        my_tz_free();
 extern my_time_t   sec_since_epoch_TIME(TIME *t);
 
-extern TABLE_LIST fake_time_zone_tables_list;
-
 /*
   Number of elements in table list produced by my_tz_get_table_list()
   (this table list contains tables which are needed for dynamical loading
@@ -77,34 +73,5 @@ extern TABLE_LIST fake_time_zone_tables_list;
 
 static const int MY_TZ_TABLES_COUNT= 4;
 
-/*
-  Check if we have pointer to the begining of list of implicitly used time
-  zone tables, set SELECT_ACL for them and fast-forward to its end.
-
-  SYNOPSIS
-    my_tz_check_n_skip_implicit_tables()
-      table     - (in/out) pointer to element of table list to check
-      tz_tables - list of implicitly used time zone tables received
-                  from my_tz_get_table_list() function.
-
-  NOTE
-    This function relies on my_tz_get_table_list() implementation.
-
-  RETURN VALUE
-    TRUE  - if table points to the beggining of tz_tables list
-    FALSE - otherwise.
-*/
-inline bool my_tz_check_n_skip_implicit_tables(TABLE_LIST **table,
-                                               TABLE_LIST *tz_tables)
-{
-  if (*table == tz_tables)
-  {
-    for (int i= 0; i < MY_TZ_TABLES_COUNT; i++)
-      (*table)[i].grant.privilege= SELECT_ACL;
-    (*table)+= MY_TZ_TABLES_COUNT - 1;
-    return TRUE;
-  }
-  return FALSE;
-}
 
 #endif /* !defined(TESTTIME) && !defined(TZINFO2SQL) */