A pre-requisite patch for the fix for Bug#52044.

This patch also fixes Bug#55452 "SET PASSWORD is
replicated twice in RBR mode".

The goal of this patch is to remove the release of 
metadata locks from close_thread_tables().
This is necessary to not mistakenly release
the locks in the course of a multi-step
operation that involves multiple close_thread_tables()
or close_tables_for_reopen().

On the same token, move statement commit outside 
close_thread_tables().

Other cleanups:
Cleanup COM_FIELD_LIST.
Don't call close_thread_tables() in COM_SHUTDOWN -- there
are no open tables there that can be closed (we leave
the locked tables mode in THD destructor, and this
close_thread_tables() won't leave it anyway).

Make open_and_lock_tables() and open_and_lock_tables_derived()
call close_thread_tables() upon failure.
Remove the calls to close_thread_tables() that are now
unnecessary.

Simplify the back off condition in Open_table_context.

Streamline metadata lock handling in LOCK TABLES 
implementation.

Add asserts to ensure correct life cycle of 
statement transaction in a session.

Remove a piece of dead code that has also become redundant
after the fix for Bug 37521.

1 files changed, 11 insertions, 4 deletions

diff --git a/sql/sys_vars.cc b/sql/sys_vars.cc
index 6e95961ebb0..9e212fb95e9 100644
--- a/sql/sys_vars.cc
+++ b/sql/sys_vars.cc
@@ -2203,14 +2203,21 @@ static bool fix_autocommit(sys_var *self, THD *thd, enum_var_type type)
       thd->variables.option_bits & OPTION_NOT_AUTOCOMMIT)
   { // activating autocommit
 
-    if (trans_commit(thd))
+    if (trans_commit_stmt(thd) || trans_commit(thd))
     {
       thd->variables.option_bits&= ~OPTION_AUTOCOMMIT;
       return true;
     }
-    close_thread_tables(thd);
-    thd->mdl_context.release_transactional_locks();
-
+    /*
+      Don't close thread tables or release metadata locks: if we do so, we
+      risk releasing locks/closing tables of expressions used to assign
+      other variables, as in:
+      set @var=my_stored_function1(), @@autocommit=1, @var2=(select max(a)
+      from my_table), ...
+      The locks will be released at statement end anyway, as SET
+      statement that assigns autocommit is marked to commit
+      transaction implicitly at the end (@sa stmt_causes_implicitcommit()).
+    */
     thd->variables.option_bits&=
                  ~(OPTION_BEGIN | OPTION_KEEP_LOG | OPTION_NOT_AUTOCOMMIT);
     thd->transaction.all.modified_non_trans_table= false;