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From:Konstantin Osipov Date:July 17 2009 5:48am
Subject:Re: bzr commit into mysql-6.0-backup branch (ingo.struewing:2825)
Bug#20667
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* Konstantin Osipov <kostja@stripped> [09/07/17 02:00]:
> I wrote a comment about that. Please see the patch at the end of
> the reply. Note that my patch is a sketch, please feel free to
> improve on it.

Correction: the last version of the patch. For some reason I sent
you an older version at first.


=== modified file 'sql/sql_delete.cc'
--- sql/sql_delete.cc	2009-06-19 09:28:44 +0000
+++ sql/sql_delete.cc	2009-07-16 19:34:47 +0000
@@ -1084,6 +1084,12 @@ bool mysql_truncate(THD *thd, TABLE_LIST
   bool error;
   uint path_length;
   MDL_request *mdl_request= NULL;
+  /*
+    Is set if we're under LOCK TABLES, and used
+    to downgrade the exclusive lock after the
+    table was truncated.
+  */
+  MDL_ticket *mdl_ticket= NULL;
   Ha_global_schema_lock_guard global_schema_lock_guard(thd);
   DBUG_ENTER("mysql_truncate");
 
@@ -1129,6 +1135,12 @@ bool mysql_truncate(THD *thd, TABLE_LIST
   if (!dont_send_ok)
   {
     enum legacy_db_type table_type;
+    /*
+      FIXME: Code of TRUNCATE breaks the meta-data
+      locking protocol since it tries to find out the table storage
+      engine and therefore accesses table in some way without holding
+      any kind of meta-data lock.
+    */
     mysql_frm_type(thd, path, &table_type);
     if (table_type == DB_TYPE_UNKNOWN)
     {
@@ -1143,24 +1155,47 @@ bool mysql_truncate(THD *thd, TABLE_LIST
 
     if (table_type == DB_TYPE_NDBCLUSTER)
       global_schema_lock_guard.lock();
-    /*
-      FIXME: Actually code of TRUNCATE breaks meta-data locking protocol since
-             tries to get table enging and therefore accesses table in some way
-             without holding any kind of meta-data lock.
-    */
-    mdl_request= MDL_request::create(0, table_list->db,
-                                     table_list->table_name, thd->mem_root);
-    mdl_request->set_type(MDL_EXCLUSIVE);
-    thd->mdl_context.add_request(mdl_request);
-    if (thd->mdl_context.acquire_exclusive_locks())
+
+    mysql_ha_rm_tables(thd, table_list);
+
+    if (thd->locked_tables_mode)
     {
-      thd->mdl_context.remove_request(mdl_request);
-      DBUG_RETURN(TRUE);
+      if (!(table= find_write_locked_table(thd->open_tables, table_list->db,
+                                           table_list->table_name)))
+        DBUG_RETURN(TRUE);
+      mdl_ticket= table->mdl_ticket;
+      if (wait_while_table_is_used(thd, table, HA_EXTRA_FORCE_REOPEN))
+        goto end;
+      close_all_tables_for_name(thd, table->s, FALSE);
+    }
+    else
+    {
+      /*
+        Even though we could use the previous execution branch
+        here just as well, we must not try to open the table: 
+        MySQL manual documents that TRUNCATE can be used to 
+        repair a damaged table, i.e. a table that can not be
+        fully "opened". In particular MySQL manual says:
+
+        As long as the table format file tbl_name.frm  is valid,
+        the table can be re-created as an empty table with TRUNCATE
+        TABLE, even if the data or index files have become corrupted.
+      */
+
+      mdl_request= MDL_request::create(0, table_list->db,
+                                       table_list->table_name, thd->mem_root);
+      mdl_request->set_type(MDL_EXCLUSIVE);
+      thd->mdl_context.add_request(mdl_request);
+      if (thd->mdl_context.acquire_exclusive_locks())
+      {
+        thd->mdl_context.remove_request(mdl_request);
+        DBUG_RETURN(TRUE);
+      }
+      pthread_mutex_lock(&LOCK_open);
+      tdc_remove_table(thd, TDC_RT_REMOVE_ALL, table_list->db,
+                       table_list->table_name);
+      pthread_mutex_unlock(&LOCK_open);
     }
-    pthread_mutex_lock(&LOCK_open);
-    tdc_remove_table(thd, TDC_RT_REMOVE_ALL, table_list->db,
-                     table_list->table_name);
-    pthread_mutex_unlock(&LOCK_open);
   }
 
   /*
@@ -1178,6 +1213,12 @@ bool mysql_truncate(THD *thd, TABLE_LIST
 end:
   if (!dont_send_ok)
   {
+    if (thd->locked_tables_mode &&
thd->locked_tables_list.reopen_tables(thd))
+      thd->locked_tables_list.unlink_all_closed_tables();
+    /*
+      Even if we failed to reopen some tables,
+      the operation itself succeeded, write the binlog.
+    */
     if (!error)
     {
       /*
@@ -1192,14 +1233,8 @@ end:
       thd->mdl_context.release_lock(mdl_request->ticket);
       thd->mdl_context.remove_request(mdl_request);
     }
-  }
-  else if (error)
-  {
-    if (mdl_request)
-    {
-      thd->mdl_context.release_lock(mdl_request->ticket);
-      thd->mdl_context.remove_request(mdl_request);
-    }
+    if (mdl_ticket)
+      mdl_ticket->downgrade_exclusive_lock();
   }
   DBUG_RETURN(error);
 

=== modified file 'sql/sql_parse.cc'
--- sql/sql_parse.cc	2009-07-10 12:31:32 +0000
+++ sql/sql_parse.cc	2009-07-16 17:13:55 +0000
@@ -3316,7 +3316,7 @@ end_with_restore_list:
       Don't allow this within a transaction because we want to use
       re-generate table
     */
-    if (thd->locked_tables_mode || thd->active_transaction())
+    if (thd->active_transaction())
     {
       my_message(ER_LOCK_OR_ACTIVE_TRANSACTION,
                  ER(ER_LOCK_OR_ACTIVE_TRANSACTION), MYF(0));

-- 
Thread
bzr commit into mysql-6.0-backup branch (ingo.struewing:2825) Bug#20667Ingo Struewing19 Jun
  • Re: bzr commit into mysql-6.0-backup branch (ingo.struewing:2825)Bug#20667Konstantin Osipov16 Jul
    • Re: bzr commit into mysql-6.0-backup branch (ingo.struewing:2825)Bug#20667Konstantin Osipov17 Jul