Backport of:

------------------------------------------------------------
revno: 2630.4.24
committer: Dmitry Lenev <dlenev@mysql.com>
branch nick: mysql-6.0-3726-w2
timestamp: Fri 2008-06-06 14:28:58 +0400
message:
  WL#3726 "DDL locking for all metadata objects".

  After review fixes in progress.

  Get rid of upgradability and priority attributes of
  metadata lock requests by replacing them with two
  new types of lock requests MDL_SHARED_UPGRADABLE and
  MDL_SHARED_HIGH_PRIO correspondingly.

sql/mdl.h

@@ -26,24 +26,25 @@ struct MDL_LOCK_DATA;
 struct MDL_LOCK;
 struct MDL_CONTEXT;
 
-/** Type of metadata lock request. */
-
-enum enum_mdl_type {MDL_SHARED=0, MDL_EXCLUSIVE};
+/**
+   Type of metadata lock request.
 
+   - High-priority shared locks differ from ordinary shared locks by
+     that they ignore pending requests for exclusive locks.
+   - Upgradable shared locks can be later upgraded to exclusive
+     (because of that their acquisition involves implicit
+      acquisition of global intention-exclusive lock).
 
-/** States which metadata lock request can have. */
+   @see Comments for can_grant_lock() and can_grant_global_lock() for details.
+*/
 
-enum enum_mdl_state {MDL_PENDING=0, MDL_ACQUIRED, MDL_PENDING_UPGRADE};
+enum enum_mdl_type {MDL_SHARED=0, MDL_SHARED_HIGH_PRIO,
+                    MDL_SHARED_UPGRADABLE, MDL_EXCLUSIVE};
 
 
-/**
-   Priority of metadata lock requests. High priority attribute is
-   applicable only to requests for shared locks and indicates that
-   such request should ignore pending requests for exclusive locks
-   and for upgrading of shared locks to exclusive.
-*/
+/** States which metadata lock request can have. */
 
-enum enum_mdl_prio {MDL_NORMAL_PRIO=0, MDL_HIGH_PRIO};
+enum enum_mdl_state {MDL_PENDING=0, MDL_ACQUIRED, MDL_PENDING_UPGRADE};
 
 
 /**
@@ -60,13 +61,6 @@ struct MDL_LOCK_DATA
   uint          key_length;
   enum          enum_mdl_type type;
   enum          enum_mdl_state state;
-  enum          enum_mdl_prio prio;
-  /**
-     TRUE -- if shared lock corresponding to this lock request at some
-     point might be upgraded to an exclusive lock and therefore conflicts
-     with global shared lock, FALSE -- otherwise.
-  */
-  bool          is_upgradable;
 
 private:
   /**
@@ -170,28 +164,6 @@ inline void mdl_set_lock_type(MDL_LOCK_DATA *lock_data, enum_mdl_type lock_type)
   lock_data->type= lock_type;
 }
 
-/**
-   Set priority for lock request. High priority can be only set
-   for shared locks.
-*/
-
-inline void mdl_set_lock_priority(MDL_LOCK_DATA *lock_data, enum_mdl_prio prio)
-{
-  DBUG_ASSERT(lock_data->type == MDL_SHARED && lock_data->state == MDL_PENDING);
-  lock_data->prio= prio;
-}
-
-/**
-   Mark request for shared lock as upgradable. Can be only applied
-   to pending locks.
-*/
-
-inline void mdl_set_upgradable(MDL_LOCK_DATA *lock_data)
-{
-  DBUG_ASSERT(lock_data->type == MDL_SHARED && lock_data->state == MDL_PENDING);
-  lock_data->is_upgradable= TRUE;
-}
-
 bool mdl_acquire_shared_lock(MDL_LOCK_DATA *lock_data, bool *retry);
 bool mdl_acquire_exclusive_locks(MDL_CONTEXT *context);
 bool mdl_upgrade_shared_lock_to_exclusive(MDL_CONTEXT *context,

sql/sql_base.cc

@@ -2822,11 +2822,19 @@ TABLE *open_table(THD *thd, TABLE_LIST *table_list, MEM_ROOT *mem_root,
   {
     bool retry;
 
+    /*
+      There is no MDL_SHARED_UPGRADABLE_HIGH_PRIO type of metadata lock so we
+      want to be sure that caller doesn't pass us both flags simultaneously.
+    */
+    DBUG_ASSERT(!(flags & MYSQL_OPEN_TAKE_UPGRADABLE_MDL) ||
+                !(flags & MYSQL_LOCK_IGNORE_FLUSH));
+
     if (flags & MYSQL_OPEN_TAKE_UPGRADABLE_MDL &&
         table_list->lock_type >= TL_WRITE_ALLOW_WRITE)
-      mdl_set_upgradable(mdl_lock_data);
-    mdl_set_lock_priority(mdl_lock_data, (flags & MYSQL_LOCK_IGNORE_FLUSH) ?
-                                         MDL_HIGH_PRIO : MDL_NORMAL_PRIO);
+      mdl_set_lock_type(mdl_lock_data, MDL_SHARED_UPGRADABLE);
+    if (flags & MYSQL_LOCK_IGNORE_FLUSH)
+      mdl_set_lock_type(mdl_lock_data, MDL_SHARED_HIGH_PRIO);
+
     if (mdl_acquire_shared_lock(mdl_lock_data, &retry))
     {
       if (retry)

sql/sql_show.cc

@@ -3136,7 +3136,7 @@ static int fill_schema_table_from_frm(THD *thd,TABLE *table,
   mdl_init_lock(&mdl_lock_data, mdlkey, 0, db_name->str, table_name->str);
   table_list.mdl_lock_data= &mdl_lock_data;
   mdl_add_lock(&thd->mdl_context, &mdl_lock_data);
-  mdl_set_lock_priority(&mdl_lock_data, MDL_HIGH_PRIO);
+  mdl_set_lock_type(&mdl_lock_data, MDL_SHARED_HIGH_PRIO);
 
   /*
     TODO: investigate if in this particular situation we can get by