MDEV-38632 ALTER EVENT doesn't re-run one-time AT event after first execution

mysql-test/main/mdev38632_alter_onetime_event.result

@@ -0,0 +1,88 @@
+SET GLOBAL event_scheduler = ON;
+CREATE TABLE test.event_log (id INT AUTO_INCREMENT PRIMARY KEY, ts TIMESTAMP DEFAULT CURRENT_TIMESTAMP);
+#
+# Step 1: Create a one-time AT event with ON COMPLETION PRESERVE
+#
+CREATE EVENT test.mdev38632
+ON SCHEDULE AT CURRENT_TIMESTAMP + INTERVAL 1 SECOND
+ON COMPLETION PRESERVE ENABLE
+DO INSERT INTO test.event_log(id) VALUES (NULL);
+# Wait for the event to execute
+SELECT COUNT(*) AS exec_count FROM test.event_log;
+exec_count
+1
+# Verify: event executed, status is now DISABLED (preserved but done)
+SELECT status, on_completion, last_executed IS NOT NULL AS has_last_exec
+FROM mysql.event WHERE db = 'test' AND name = 'mdev38632';
+status	on_completion	has_last_exec
+DISABLED	PRESERVE	1
+#
+# Step 2: ALTER EVENT to reschedule — without explicit ENABLE
+# This is the customer's scenario from the JIRA report.
+#
+ALTER EVENT test.mdev38632
+ON SCHEDULE AT CURRENT_TIMESTAMP + INTERVAL 1 SECOND;
+# After ALTER with a new schedule, status should be re-enabled automatically.
+SELECT status FROM mysql.event WHERE db = 'test' AND name = 'mdev38632';
+status
+ENABLED
+# The event should fire again after being rescheduled.
+SELECT COUNT(*) AS exec_count FROM test.event_log;
+exec_count
+2
+#
+# Step 3: Try again with explicit ENABLE — verify scheduler reload works.
+#
+ALTER EVENT test.mdev38632
+ON SCHEDULE AT CURRENT_TIMESTAMP + INTERVAL 1 SECOND
+ON COMPLETION PRESERVE ENABLE;
+# After fix, last_executed should be cleared when schedule changes.
+SELECT status, last_executed IS NOT NULL AS has_last_exec
+FROM mysql.event WHERE db = 'test' AND name = 'mdev38632';
+status	has_last_exec
+ENABLED	0
+# Restart the scheduler to trigger reload from mysql.event.
+# After fix, the event should remain ENABLED after reload.
+SET GLOBAL event_scheduler = OFF;
+SET GLOBAL event_scheduler = ON;
+# Status should remain ENABLED after scheduler reload.
+SELECT status FROM mysql.event WHERE db = 'test' AND name = 'mdev38632';
+status
+ENABLED
+#
+# Step 4: User-disabled event should NOT be re-enabled by reschedule
+#
+ALTER EVENT test.mdev38632
+ON SCHEDULE AT CURRENT_TIMESTAMP + INTERVAL 1 HOUR
+ON COMPLETION PRESERVE ENABLE;
+ALTER EVENT test.mdev38632 DISABLE;
+SELECT status FROM mysql.event WHERE db = 'test' AND name = 'mdev38632';
+status
+DISABLED
+# Reschedule without explicit ENABLE — should stay DISABLED
+ALTER EVENT test.mdev38632
+ON SCHEDULE AT CURRENT_TIMESTAMP + INTERVAL 2 HOUR;
+SELECT status FROM mysql.event WHERE db = 'test' AND name = 'mdev38632';
+status
+DISABLED
+#
+# Step 5: ALTER with same execute_at should not clear last_executed
+#
+DROP EVENT test.mdev38632;
+CREATE EVENT test.mdev38632
+ON SCHEDULE AT CURRENT_TIMESTAMP + INTERVAL 1 SECOND
+ON COMPLETION PRESERVE ENABLE
+DO INSERT INTO test.event_log(id) VALUES (NULL);
+# Event executed, now ALTER with same body but no schedule change
+ALTER EVENT test.mdev38632
+DO INSERT INTO test.event_log(id) VALUES (NULL);
+# Status should remain DISABLED (no schedule change, no re-enable)
+SELECT status FROM mysql.event WHERE db = 'test' AND name = 'mdev38632';
+status
+DISABLED
+#
+# Cleanup
+#
+DROP EVENT IF EXISTS test.mdev38632;
+DROP TABLE test.event_log;
+SET GLOBAL event_scheduler = OFF;

mysql-test/main/mdev38632_alter_onetime_event.test

@@ -0,0 +1,119 @@
+#
+# MDEV-38632: ALTER EVENT doesn't run a one-time (AT) event after its first
+# execution when ON COMPLETION PRESERVE is used.
+#
+# After an AT event with ON COMPLETION PRESERVE executes:
+#   1. compute_next_execution_time() sets status=DISABLED in mysql.event
+#   2. ALTER EVENT without explicit ENABLE does not reset the status
+#   3. The event queue refuses to queue a DISABLED event
+#   4. Even with explicit ENABLE, last_executed causes re-disable on reload
+#
+# Expected fix: ALTER EVENT with a new schedule should re-enable the event
+# and clear last_executed so it is properly queued.
+#
+
+--source include/not_embedded.inc
+
+SET GLOBAL event_scheduler = ON;
+--source include/running_event_scheduler.inc
+
+CREATE TABLE test.event_log (id INT AUTO_INCREMENT PRIMARY KEY, ts TIMESTAMP DEFAULT CURRENT_TIMESTAMP);
+
+--echo #
+--echo # Step 1: Create a one-time AT event with ON COMPLETION PRESERVE
+--echo #
+CREATE EVENT test.mdev38632
+  ON SCHEDULE AT CURRENT_TIMESTAMP + INTERVAL 1 SECOND
+  ON COMPLETION PRESERVE ENABLE
+  DO INSERT INTO test.event_log(id) VALUES (NULL);
+
+--echo # Wait for the event to execute
+let $wait_condition = SELECT COUNT(*) >= 1 FROM test.event_log;
+--source include/wait_condition.inc
+
+SELECT COUNT(*) AS exec_count FROM test.event_log;
+
+--echo # Verify: event executed, status is now DISABLED (preserved but done)
+SELECT status, on_completion, last_executed IS NOT NULL AS has_last_exec
+  FROM mysql.event WHERE db = 'test' AND name = 'mdev38632';
+
+--echo #
+--echo # Step 2: ALTER EVENT to reschedule — without explicit ENABLE
+--echo # This is the customer's scenario from the JIRA report.
+--echo #
+ALTER EVENT test.mdev38632
+  ON SCHEDULE AT CURRENT_TIMESTAMP + INTERVAL 1 SECOND;
+
+--echo # After ALTER with a new schedule, status should be re-enabled automatically.
+SELECT status FROM mysql.event WHERE db = 'test' AND name = 'mdev38632';
+
+--echo # The event should fire again after being rescheduled.
+let $wait_condition = SELECT COUNT(*) >= 2 FROM test.event_log;
+--source include/wait_condition.inc
+
+SELECT COUNT(*) AS exec_count FROM test.event_log;
+
+--echo #
+--echo # Step 3: Try again with explicit ENABLE — verify scheduler reload works.
+--echo #
+ALTER EVENT test.mdev38632
+  ON SCHEDULE AT CURRENT_TIMESTAMP + INTERVAL 1 SECOND
+  ON COMPLETION PRESERVE ENABLE;
+
+--echo # After fix, last_executed should be cleared when schedule changes.
+SELECT status, last_executed IS NOT NULL AS has_last_exec
+  FROM mysql.event WHERE db = 'test' AND name = 'mdev38632';
+
+--echo # Restart the scheduler to trigger reload from mysql.event.
+--echo # After fix, the event should remain ENABLED after reload.
+SET GLOBAL event_scheduler = OFF;
+--source include/check_events_off.inc
+SET GLOBAL event_scheduler = ON;
+--source include/running_event_scheduler.inc
+
+--echo # Status should remain ENABLED after scheduler reload.
+SELECT status FROM mysql.event WHERE db = 'test' AND name = 'mdev38632';
+
+--echo #
+--echo # Step 4: User-disabled event should NOT be re-enabled by reschedule
+--echo #
+ALTER EVENT test.mdev38632
+  ON SCHEDULE AT CURRENT_TIMESTAMP + INTERVAL 1 HOUR
+  ON COMPLETION PRESERVE ENABLE;
+
+ALTER EVENT test.mdev38632 DISABLE;
+
+SELECT status FROM mysql.event WHERE db = 'test' AND name = 'mdev38632';
+
+--echo # Reschedule without explicit ENABLE — should stay DISABLED
+ALTER EVENT test.mdev38632
+  ON SCHEDULE AT CURRENT_TIMESTAMP + INTERVAL 2 HOUR;
+
+SELECT status FROM mysql.event WHERE db = 'test' AND name = 'mdev38632';
+
+--echo #
+--echo # Step 5: ALTER with same execute_at should not clear last_executed
+--echo #
+DROP EVENT test.mdev38632;
+CREATE EVENT test.mdev38632
+  ON SCHEDULE AT CURRENT_TIMESTAMP + INTERVAL 1 SECOND
+  ON COMPLETION PRESERVE ENABLE
+  DO INSERT INTO test.event_log(id) VALUES (NULL);
+
+let $wait_condition = SELECT COUNT(*) >= 3 FROM test.event_log;
+--source include/wait_condition.inc
+
+--echo # Event executed, now ALTER with same body but no schedule change
+ALTER EVENT test.mdev38632
+  DO INSERT INTO test.event_log(id) VALUES (NULL);
+
+--echo # Status should remain DISABLED (no schedule change, no re-enable)
+SELECT status FROM mysql.event WHERE db = 'test' AND name = 'mdev38632';
+
+--echo #
+--echo # Cleanup
+--echo #
+DROP EVENT IF EXISTS test.mdev38632;
+DROP TABLE test.event_log;
+SET GLOBAL event_scheduler = OFF;
+--source include/check_events_off.inc

sql/event_data_objects.cc

@@ -948,8 +948,12 @@ Event_queue_element::compute_next_execution_time()
   /* If one-time, no need to do computation */
   if (!expression)
   {
-    /* Let's check whether it was executed */
-    if (last_executed)
+    /*
+      Check whether the event was already executed for the current schedule.
+      If execute_at was changed (via ALTER EVENT) to a time after
+      last_executed, the event should still be considered pending (MDEV-38632).
+    */
+    if (last_executed && last_executed >= execute_at)
     {
       DBUG_PRINT("info",("One-time event %s.%s of was already executed",
                          dbname.str, name.str));

sql/event_db_repository.cc

@@ -319,6 +319,54 @@ mysql_event_fill_row(THD *thd,
     MYSQL_TIME time;
     my_tz_OFFSET0->gmt_sec_to_TIME(&time, et->execute_at);
 
+    /*
+      MDEV-38632: When ALTER EVENT changes execute_at, clear last_executed
+      and re-enable the event if it was auto-disabled by the scheduler.
+
+      Only act when execute_at actually changed. Compare the new value
+      against the stored one before overwriting.
+
+      Re-enable only if: the user didn't explicitly set status, the stored
+      status is DISABLED, and last_executed >= old execute_at (meaning the
+      scheduler disabled it after running at that time).
+
+      Note: this heuristic cannot distinguish "scheduler auto-disabled"
+      from "user explicitly disabled an already-auto-disabled event"
+      since both states look identical in mysql.event. In the rare case
+      where a user explicitly disables an already-disabled event and then
+      reschedules it, the event would be incorrectly re-enabled.
+    */
+    if (is_update)
+    {
+      bool schedule_changed= true;
+      MYSQL_TIME old_execute_at;
+
+      if (!fields[ET_FIELD_EXECUTE_AT]->is_null() &&
+          !fields[ET_FIELD_EXECUTE_AT]->get_date(&old_execute_at,
+                                                 TIME_NO_ZERO_DATE |
+                                                 thd->temporal_round_mode()))
+        schedule_changed= my_time_compare(&time, &old_execute_at) != 0;
+
+      if (schedule_changed)
+      {
+        if (!et->status_changed &&
+            fields[ET_FIELD_STATUS]->val_int() == Event_parse_data::DISABLED &&
+            !fields[ET_FIELD_LAST_EXECUTED]->is_null())
+        {
+          MYSQL_TIME old_last_executed;
+          if (!fields[ET_FIELD_LAST_EXECUTED]->get_date(&old_last_executed,
+                                                        TIME_NO_ZERO_DATE |
+                                                        thd->temporal_round_mode()))
+          {
+            if (my_time_compare(&old_last_executed, &old_execute_at) >= 0)
+              rs|= fields[ET_FIELD_STATUS]->store(
+                       (longlong)Event_parse_data::ENABLED, TRUE);
+          }
+        }
+        fields[ET_FIELD_LAST_EXECUTED]->set_null();
+      }
+    }
+
     fields[ET_FIELD_EXECUTE_AT]->set_notnull();
     fields[ET_FIELD_EXECUTE_AT]->store_time(&time);
   }