Fix for bug #35732: read-only blocks SELECT statements in InnoDB

Problem: SELECTs prohibited for a transactional SE in autocommit mode
if read_only is set.

Fix: allow them.


mysql-test/r/read_only_innodb.result:
  Fix for bug #35732: read-only blocks SELECT statements in InnoDB
    - test result.
mysql-test/t/read_only_innodb.test:
  Fix for bug #35732: read-only blocks SELECT statements in InnoDB
    - test case.
sql/handler.cc:
  Fix for bug #35732: read-only blocks SELECT statements in InnoDB
    - in autocommit mode thd->transaction.all list is empty thus 
      is_real_trans set to TRUE for any SELECTs, so using it in the
      "read_only" check is insufficient.
      ha_check_and_coalesce_trx_read_only() changed to return number
      of engines with read-write changes. This value is used in the
      "read-only" check and checks for GLOBAL READ LOCK.
sql/lock.cc:
  Fix for bug #35732: read-only blocks SELECT statements in InnoDB
    - added assert(protect_against_global_read_lock) before decreasing,
      in order to catch (uint) 0 - 1 situation due to wrong 
      wait_if_global_read_lock()/start_waiting_global_read_lock() call
      sequence.

1 files changed, 1 insertions, 0 deletions

diff --git a/sql/lock.cc b/sql/lock.cc
index a0d6faa6604..675b94c2175 100644
--- a/sql/lock.cc
+++ b/sql/lock.cc
@@ -1533,6 +1533,7 @@ void start_waiting_global_read_lock(THD *thd)
   if (unlikely(thd->global_read_lock))
     DBUG_VOID_RETURN;
   (void) pthread_mutex_lock(&LOCK_global_read_lock);
+  DBUG_ASSERT(protect_against_global_read_lock);
   tmp= (!--protect_against_global_read_lock &&
         (waiting_for_read_lock || global_read_lock_blocks_commit));
   (void) pthread_mutex_unlock(&LOCK_global_read_lock);