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.

2 files changed, 17 insertions, 0 deletions

diff --git a/storage/myisammrg/ha_myisammrg.cc b/storage/myisammrg/ha_myisammrg.cc
index 26e54d61101..79696cad721 100644
--- a/storage/myisammrg/ha_myisammrg.cc
+++ b/storage/myisammrg/ha_myisammrg.cc
@@ -1226,6 +1226,22 @@ ha_rows ha_myisammrg::records_in_range(uint inx, key_range *min_key,
 }
 
 
+int ha_myisammrg::truncate()
+{
+  int err= 0;
+  MYRG_TABLE *table;
+  DBUG_ENTER("ha_myisammrg::truncate");
+
+  for (table= file->open_tables; table != file->end_table; table++)
+  {
+    if ((err= mi_delete_all_rows(table->table)))
+      break;
+  }
+
+  DBUG_RETURN(err);
+}
+
+
 int ha_myisammrg::info(uint flag)
 {
   MYMERGE_INFO mrg_info;
diff --git a/storage/myisammrg/ha_myisammrg.h b/storage/myisammrg/ha_myisammrg.h
index 4ff24c69071..cae4bd17f50 100644
--- a/storage/myisammrg/ha_myisammrg.h
+++ b/storage/myisammrg/ha_myisammrg.h
@@ -131,6 +131,7 @@ public:
   int rnd_pos(uchar * buf, uchar *pos);
   void position(const uchar *record);
   ha_rows records_in_range(uint inx, key_range *min_key, key_range *max_key);
+  int truncate();
   int info(uint);
   int reset(void);
   int extra(enum ha_extra_function operation);