Fixed bug#12546938 (formerly known as 61005) - CREATE IF NOT EXIST EVENT

will create multiple running events.

A CREATE IF NOT EXIST on an event that existed and was enabled caused
multiple instances of the event to run. Disabling the event didn't  help.
If the event was  dropped, the event stopped running, but when created
again, multiple instances of the event were still running. The only way
to get out of this situation was  to restart the server.

The problem was that Event_db_repository::create_event() didn't return
enough information to discriminate between situation when event didn't
exist and was created and when event did exist and was not created
(but a warning was emitted). As result in the latter case event
was added to in-memory queue of events second time. And this led to
unwarranted multiple executions of the same event.

The solution is to add out-parameter to Event_db_repository::create_event()
method which will signal that event was not created because it already
exists and so it should not be added to the in-memory queue.


mysql-test/r/events_bugs.result:
  Added results for test for Bug#12546938.
mysql-test/t/events_bugs.test:
  Added test for Bug#12546938.
sql/event_db_repository.cc:
  Event_db_repository::create_event was modified: set newly added out-parameter
  event_already_exists to true value if event wasn't created because event
  already existed and IF NOT EXIST clause was present.
sql/event_db_repository.h:
  Added out-parameter 'event_already_exists' to create_event() method.
sql/events.cc:
  Events::create_event was modified: insert new element into
  event queue only if event was actually created.

3 files changed, 46 insertions, 33 deletions

diff --git a/sql/event_db_repository.cc b/sql/event_db_repository.cc
index a0765dc6d15..9efd3bca675 100644
--- a/sql/event_db_repository.cc
+++ b/sql/event_db_repository.cc
@@ -604,18 +604,21 @@ Event_db_repository::open_event_table(THD *thd, enum thr_lock_type lock_type,
   only creates a record on disk.
   @pre The thread handle has no open tables.
 
-  @param[in,out] thd           THD
-  @param[in]     parse_data    Parsed event definition
-  @param[in]     create_if_not TRUE if IF NOT EXISTS clause was provided
-                               to CREATE EVENT statement
-
+  @param[in,out] thd                   THD
+  @param[in]     parse_data            Parsed event definition
+  @param[in]     create_if_not         TRUE if IF NOT EXISTS clause was provided
+                                       to CREATE EVENT statement
+  @param[out]    event_already_exists  When method is completed successfully
+                                       set to true if event already exists else
+                                       set to false
   @retval FALSE  success
   @retval TRUE   error
 */
 
 bool
 Event_db_repository::create_event(THD *thd, Event_parse_data *parse_data,
-                                  my_bool create_if_not)
+                                  bool create_if_not,
+                                  bool *event_already_exists)
 {
   int ret= 1;
   TABLE *table= NULL;
@@ -641,6 +644,7 @@ Event_db_repository::create_event(THD *thd, Event_parse_data *parse_data,
   {
     if (create_if_not)
     {
+      *event_already_exists= true;
       push_warning_printf(thd, MYSQL_ERROR::WARN_LEVEL_NOTE,
                           ER_EVENT_ALREADY_EXISTS, ER(ER_EVENT_ALREADY_EXISTS),
                           parse_data->name.str);
@@ -648,8 +652,10 @@ Event_db_repository::create_event(THD *thd, Event_parse_data *parse_data,
     }
     else
       my_error(ER_EVENT_ALREADY_EXISTS, MYF(0), parse_data->name.str);
+
     goto end;
-  }
+  } else
+    *event_already_exists= false;
 
   DBUG_PRINT("info", ("non-existent, go forward"));
 
diff --git a/sql/event_db_repository.h b/sql/event_db_repository.h
index ef778407d1e..a7d7b97ae3c 100644
--- a/sql/event_db_repository.h
+++ b/sql/event_db_repository.h
@@ -73,7 +73,8 @@ public:
   Event_db_repository(){}
 
   bool
-  create_event(THD *thd, Event_parse_data *parse_data, my_bool create_if_not);
+  create_event(THD *thd, Event_parse_data *parse_data, bool create_if_not,
+               bool *event_already_exists);
 
   bool
   update_event(THD *thd, Event_parse_data *parse_data, LEX_STRING *new_dbname,
diff --git a/sql/events.cc b/sql/events.cc
index 7edd863ac41..08360ee5f04 100644
--- a/sql/events.cc
+++ b/sql/events.cc
@@ -370,6 +370,7 @@ create_query_string(THD *thd, String *buf)
   return 0;
 }
 
+
 /**
   Create a new event.
 
@@ -390,8 +391,8 @@ bool
 Events::create_event(THD *thd, Event_parse_data *parse_data,
                      bool if_not_exists)
 {
-  int ret;
-  bool save_binlog_row_based;
+  bool ret;
+  bool save_binlog_row_based, event_already_exists;
   DBUG_ENTER("Events::create_event");
 
   /*
@@ -440,28 +441,32 @@ Events::create_event(THD *thd, Event_parse_data *parse_data,
   pthread_mutex_lock(&LOCK_event_metadata);
 
   /* On error conditions my_error() is called so no need to handle here */
-  if (!(ret= db_repository->create_event(thd, parse_data, if_not_exists)))
+  if (!(ret= db_repository->create_event(thd, parse_data, if_not_exists,
+                                         &event_already_exists)))
   {
     Event_queue_element *new_element;
     bool dropped= 0;
 
-    if (!(new_element= new Event_queue_element()))
-      ret= TRUE;                                // OOM
-    else if ((ret= db_repository->load_named_event(thd, parse_data->dbname,
-                                                   parse_data->name,
-                                                   new_element)))
-    {
-      if (!db_repository->drop_event(thd, parse_data->dbname, parse_data->name,
-                                     TRUE))
-        dropped= 1;
-      delete new_element;
-    }
-    else
+    if (!event_already_exists)
     {
-      /* TODO: do not ignore the out parameter and a possible OOM error! */
-      bool created;
-      if (event_queue)
-        event_queue->create_event(thd, new_element, &created);
+      if (!(new_element= new Event_queue_element()))
+        ret= TRUE;                                // OOM
+      else if ((ret= db_repository->load_named_event(thd, parse_data->dbname,
+                                                     parse_data->name,
+                                                     new_element)))
+      {
+        if (!db_repository->drop_event(thd, parse_data->dbname, parse_data->name,
+                                       TRUE))
+          dropped= 1;
+        delete new_element;
+      }
+      else
+      {
+        /* TODO: do not ignore the out parameter and a possible OOM error! */
+        bool created;
+        if (event_queue)
+          event_queue->create_event(thd, new_element, &created);
+      }
     }
     /*
       binlog the create event unless it's been successfully dropped
@@ -475,13 +480,14 @@ Events::create_event(THD *thd, Event_parse_data *parse_data,
       {
         sql_print_error("Event Error: An error occurred while creating query string, "
                         "before writing it into binary log.");
-        /* Restore the state of binlog format */
-        thd->current_stmt_binlog_row_based= save_binlog_row_based;
-        DBUG_RETURN(TRUE);
+        ret= true;
       }
-      /* If the definer is not set or set to CURRENT_USER, the value of CURRENT_USER 
-         will be written into the binary log as the definer for the SQL thread. */
-      ret= write_bin_log(thd, TRUE, log_query.c_ptr(), log_query.length());
+      else
+        /*
+          If the definer is not set or set to CURRENT_USER, the value of CURRENT_USER
+          will be written into the binary log as the definer for the SQL thread.
+        */
+        ret= write_bin_log(thd, TRUE, log_query.c_ptr(), log_query.length());
     }
   }
   pthread_mutex_unlock(&LOCK_event_metadata);