Fix for bug#14188793 - "DEADLOCK CAUSED BY ALTER TABLE DOEN'T CLEAR

STATUS OF ROLLBACKED TRANSACTION" and bug #17054007 - "TRANSACTION
IS NOT FULLY ROLLED BACK IN CASE OF INNODB DEADLOCK".

The problem in the first bug report was that although deadlock involving
metadata locks was reported using the same error code and message as InnoDB
deadlock it didn't rollback transaction like the latter. This caused
confusion to users as in some cases after ER_LOCK_DEADLOCK transaction
could have been restarted immediately and in some cases rollback was
required.

The problem in the second bug report was that although InnoDB deadlock
caused transaction rollback in all storage engines it didn't cause release
of metadata locks. So concurrent DDL on the tables used in transaction was
blocked until implicit or explicit COMMIT or ROLLBACK was issued in the
connection which got InnoDB deadlock.

The former issue has stemmed from the fact that when support for detection
and reporting metadata locks deadlocks was added we erroneously assumed
that InnoDB doesn't rollback transaction on deadlock but only last statement
(while this is what happens on InnoDB lock timeout actually) and so didn't
implement rollback of transactions on MDL deadlocks.

The latter issue was caused by the fact that rollback of transaction due
to deadlock is carried out by setting THD::transaction_rollback_request
flag at the point where deadlock is detected and performing rollback
inside of trans_rollback_stmt() call when this flag is set. And
trans_rollback_stmt() is not aware of MDL locks, so no MDL locks are
released.

This patch solves these two problems in the following way:

- In case when MDL deadlock is detect transaction rollback is requested
  by setting THD::transaction_rollback_request flag.

- Code performing rollback of transaction if THD::transaction_rollback_request
  is moved out from trans_rollback_stmt(). Now we handle rollback request
  on the same level as we call trans_rollback_stmt() and release statement/
  transaction MDL locks.

1 files changed, 11 insertions, 1 deletions

diff --git a/sql/log_event.cc b/sql/log_event.cc
index d2682a3eb9e..31ee950dbe4 100644
--- a/sql/log_event.cc
+++ b/sql/log_event.cc
@@ -5104,6 +5104,8 @@ error:
   thd->stmt_da->can_overwrite_status= FALSE;
   close_thread_tables(thd);
   /*
+    - If transaction rollback was requested due to deadlock
+      perform it and release metadata locks.
     - If inside a multi-statement transaction,
     defer the release of metadata locks until the current
     transaction is either committed or rolled back. This prevents
@@ -5113,7 +5115,12 @@ error:
     - If in autocommit mode, or outside a transactional context,
     automatically release metadata locks of the current statement.
   */
-  if (! thd->in_multi_stmt_transaction_mode())
+  if (thd->transaction_rollback_request)
+  {
+    trans_rollback_implicit(thd);
+    thd->mdl_context.release_transactional_locks();
+  }
+  else if (! thd->in_multi_stmt_transaction_mode())
     thd->mdl_context.release_transactional_locks();
   else
     thd->mdl_context.release_statement_locks();
@@ -8197,7 +8204,10 @@ static int rows_event_stmt_cleanup(Relay_log_info const *rli, THD * thd)
       Xid_log_event will come next which will, if some transactional engines
       are involved, commit the transaction and flush the pending event to the
       binlog.
+      If there was a deadlock the transaction should have been rolled back
+      already. So there should be no need to rollback the transaction.
     */
+    DBUG_ASSERT(! thd->transaction_rollback_request);
     error|= (error ? trans_rollback_stmt(thd) : trans_commit_stmt(thd));
 
     /*