Bug#49938: Failing assertion: inode or deadlock in fsp/fsp0fsp.c

Bug#54678: InnoDB, TRUNCATE, ALTER, I_S SELECT, crash or deadlock

- Incompatible change: truncate no longer resorts to a row by
row delete if the storage engine does not support the truncate
method. Consequently, the count of affected rows does not, in
any case, reflect the actual number of rows.

- Incompatible change: it is no longer possible to truncate a
table that participates as a parent in a foreign key constraint,
unless it is a self-referencing constraint (both parent and child
are in the same table). To work around this incompatible change
and still be able to truncate such tables, disable foreign checks
with SET foreign_key_checks=0 before truncate. Alternatively, if
foreign key checks are necessary, please use a DELETE statement
without a WHERE condition.

Problem description:

The problem was that for storage engines that do not support
truncate table via a external drop and recreate, such as InnoDB
which implements truncate via a internal drop and recreate, the
delete_all_rows method could be invoked with a shared metadata
lock, causing problems if the engine needed exclusive access
to some internal metadata. This problem originated with the
fact that there is no truncate specific handler method, which
ended up leading to a abuse of the delete_all_rows method that
is primarily used for delete operations without a condition.

Solution:

The solution is to introduce a truncate handler method that is
invoked when the engine does not support truncation via a table
drop and recreate. This method is invoked under a exclusive
metadata lock, so that there is only a single instance of the
table when the method is invoked.

Also, the method is not invoked and a error is thrown if
the table is a parent in a non-self-referencing foreign key
relationship. This was necessary to avoid inconsistency as
some integrity checks are bypassed. This is inline with the
fact that truncate is primarily a DDL operation that was
designed to quickly remove all data from a table.

1 files changed, 51 insertions, 7 deletions

diff --git a/sql/handler.h b/sql/handler.h
index b1d64a1114b..325df003215 100644
--- a/sql/handler.h
+++ b/sql/handler.h
@@ -1331,6 +1331,7 @@ public:
   int ha_bulk_update_row(const uchar *old_data, uchar *new_data,
                          uint *dup_key_found);
   int ha_delete_all_rows();
+  int ha_truncate();
   int ha_reset_auto_increment(ulonglong value);
   int ha_optimize(THD* thd, HA_CHECK_OPT* check_opt);
   int ha_analyze(THD* thd, HA_CHECK_OPT* check_opt);
@@ -1644,8 +1645,33 @@ public:
   { return(NULL);}  /* gets tablespace name from handler */
   /** used in ALTER TABLE; 1 if changing storage engine is allowed */
   virtual bool can_switch_engines() { return 1; }
-  /** used in REPLACE; is > 0 if table is referred by a FOREIGN KEY */
-  virtual int get_foreign_key_list(THD *thd, List<FOREIGN_KEY_INFO> *f_key_list)
+  /**
+    Get the list of foreign keys in this table.
+
+    @remark Returns the set of foreign keys where this table is the
+            dependent or child table.
+
+    @param thd  The thread handle.
+    @param f_key_list[out]  The list of foreign keys.
+
+    @return The handler error code or zero for success.
+  */
+  virtual int
+  get_foreign_key_list(THD *thd, List<FOREIGN_KEY_INFO> *f_key_list)
+  { return 0; }
+  /**
+    Get the list of foreign keys referencing this table.
+
+    @remark Returns the set of foreign keys where this table is the
+            referenced or parent table.
+
+    @param thd  The thread handle.
+    @param f_key_list[out]  The list of foreign keys.
+
+    @return The handler error code or zero for success.
+  */
+  virtual int
+  get_parent_foreign_key_list(THD *thd, List<FOREIGN_KEY_INFO> *f_key_list)
   { return 0; }
   virtual uint referenced_by_foreign_key() { return 0;}
   virtual void init_table_handle_for_HANDLER()
@@ -2010,16 +2036,34 @@ private:
     This is called to delete all rows in a table
     If the handler don't support this, then this function will
     return HA_ERR_WRONG_COMMAND and MySQL will delete the rows one
-    by one. It should reset auto_increment if
-    thd->lex->sql_command == SQLCOM_TRUNCATE.
+    by one.
   */
   virtual int delete_all_rows()
   { return (my_errno=HA_ERR_WRONG_COMMAND); }
   /**
+    Quickly remove all rows from a table.
+
+    @remark This method is responsible for implementing MySQL's TRUNCATE
+            TABLE statement, which is a DDL operation. As such, a engine
+            can bypass certain integrity checks and in some cases avoid
+            fine-grained locking (e.g. row locks) which would normally be
+            required for a DELETE statement.
+
+    @remark Typically, truncate is not used if it can result in integrity
+            violation. For example, truncate is not used when a foreign
+            key references the table, but it might be used if foreign key
+            checks are disabled.
+
+    @remark Engine is responsible for resetting the auto-increment counter.
+
+    @remark The table is locked in exclusive mode.
+  */
+  virtual int truncate()
+  { return HA_ERR_WRONG_COMMAND; }
+  /**
     Reset the auto-increment counter to the given value, i.e. the next row
-    inserted will get the given value. This is called e.g. after TRUNCATE
-    is emulated by doing a 'DELETE FROM t'. HA_ERR_WRONG_COMMAND is
-    returned by storage engines that don't support this operation.
+    inserted will get the given value. HA_ERR_WRONG_COMMAND is returned by
+    storage engines that don't support this operation.
   */
   virtual int reset_auto_increment(ulonglong value)
   { return HA_ERR_WRONG_COMMAND; }