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 +1,62 @@
+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
+# 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 with explicit ENABLE
+# This is the customer's scenario from the JIRA report.
+ALTER EVENT test.mdev38632
+ON SCHEDULE AT CURRENT_TIMESTAMP + INTERVAL 1 SECOND
+ON COMPLETION PRESERVE ENABLE;
+# After ALTER with ENABLE and a new schedule, last_executed should be cleared.
+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
+# The event should fire again after being rescheduled.
+# Step 3: Verify event fires after server restart (the customer scenario).
+ALTER EVENT test.mdev38632
+ON SCHEDULE AT CURRENT_TIMESTAMP + INTERVAL 3 SECOND
+ON COMPLETION PRESERVE ENABLE;
+# 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 server to trigger full reload from mysql.event.
+# restart
+SET GLOBAL event_scheduler = ON;
+# The event should fire after server restart.
+# Step 4: User-disabled event stays DISABLED after reschedule without ENABLE
+ALTER EVENT test.mdev38632 DISABLE;
+ALTER EVENT test.mdev38632
+ON SCHEDULE AT CURRENT_TIMESTAMP + INTERVAL 2 HOUR;
+# Status remains DISABLED — explicit ENABLE is required to reschedule.
+SELECT status FROM mysql.event WHERE db = 'test' AND name = 'mdev38632';
+status
+DISABLED
+# Step 5: ALTER that doesn't change schedule 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 and is DISABLED. ALTER body only (no schedule change).
+ALTER EVENT test.mdev38632
+DO INSERT INTO test.event_log(id) VALUES (NULL);
+# Status should remain DISABLED (no schedule change)
+SELECT status FROM mysql.event WHERE db = 'test' AND name = 'mdev38632';
+status
+DISABLED
+# Cleanup
+DROP EVENT test.mdev38632;
+DROP TABLE test.event_log;
+SET GLOBAL event_scheduler = OFF;

mysql-test/main/mdev38632_alter_onetime_event.test

@@ -0,0 +1,97 @@
+#
+# 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, the scheduler sets
+# status=DISABLED and last_executed in mysql.event. A subsequent ALTER EVENT
+# with explicit ENABLE and a new schedule should allow the event to fire again.
+#
+# The fix clears last_executed when execute_at changes, and only disables
+# in compute_next_execution_time() if last_executed >= execute_at.
+#
+
+--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 # 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);
+
+--echo # Wait for the event to execute
+let $wait_condition = SELECT COUNT(*) = 1 FROM test.event_log;
+--source include/wait_condition.inc
+
+--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 # Step 2: ALTER EVENT to reschedule with explicit ENABLE
+--echo # This is the customer's scenario from the JIRA report.
+ALTER EVENT test.mdev38632
+  ON SCHEDULE AT CURRENT_TIMESTAMP + INTERVAL 1 SECOND
+  ON COMPLETION PRESERVE ENABLE;
+
+--echo # After ALTER with ENABLE and a new schedule, last_executed should be cleared.
+SELECT status, last_executed IS NOT NULL AS has_last_exec
+  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
+
+--echo # Step 3: Verify event fires after server restart (the customer scenario).
+ALTER EVENT test.mdev38632
+  ON SCHEDULE AT CURRENT_TIMESTAMP + INTERVAL 3 SECOND
+  ON COMPLETION PRESERVE ENABLE;
+
+--echo # 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 server to trigger full reload from mysql.event.
+--source include/restart_mysqld.inc
+SET GLOBAL event_scheduler = ON;
+--source include/running_event_scheduler.inc
+
+--echo # The event should fire after server restart.
+--let $wait_timeout = 10
+let $wait_condition = SELECT COUNT(*) = 3 FROM test.event_log;
+--source include/wait_condition.inc
+
+--echo # Step 4: User-disabled event stays DISABLED after reschedule without ENABLE
+ALTER EVENT test.mdev38632 DISABLE;
+
+ALTER EVENT test.mdev38632
+  ON SCHEDULE AT CURRENT_TIMESTAMP + INTERVAL 2 HOUR;
+
+--echo # Status remains DISABLED — explicit ENABLE is required to reschedule.
+SELECT status FROM mysql.event WHERE db = 'test' AND name = 'mdev38632';
+
+--echo # Step 5: ALTER that doesn't change schedule 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);
+
+let $wait_condition = SELECT COUNT(*) = 4 FROM test.event_log;
+--source include/wait_condition.inc
+
+--echo # Event executed and is DISABLED. ALTER body only (no schedule change).
+ALTER EVENT test.mdev38632
+  DO INSERT INTO test.event_log(id) VALUES (NULL);
+
+--echo # Status should remain DISABLED (no schedule change)
+SELECT status FROM mysql.event WHERE db = 'test' AND name = 'mdev38632';
+
+--echo # Cleanup
+DROP EVENT 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 +319,30 @@ 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.
+      A new execute_at means the event hasn't been executed for this
+      schedule yet. Without this, compute_next_execution_time() would
+      see the stale last_executed and disable the event on reload.
+
+      Only clear when execute_at actually changed. Compare the new value
+      against the stored one before overwriting.
+    */
+    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)
+        fields[ET_FIELD_LAST_EXECUTED]->set_null();
+    }
+
     fields[ET_FIELD_EXECUTE_AT]->set_notnull();
     fields[ET_FIELD_EXECUTE_AT]->store_time(&time);
   }