Cleanup of task logs fails with big number of records to be deleted

1. Insert 100 000 records into `mdl_task_log` table: insert into mdl_task_log (type, component, classname, userid, timestart, timeend, dbreads, dbwrites, result, output) select 0, 'moodle', 'core\task\task_log_cleanup_task', 0, 1529580061+i, 1529580062+i, 5, 0,0, 'output' from generate_series(1,100000) i;  2. Run scheduled task: php admin/tool/task/cli/schedule_task.php --showdebugging --execute='\core\task\task_log_cleanup_task'  3.  Confirm , that the task exits with no error: root @c3a08300483e :/siteroot# php admin/tool/task/cli/schedule_task.php --showdebugging --execute= '\core\task\task_log_cleanup_task' Execute scheduled task: Cleanup of task logs (core\task\task_log_cleanup_task) ... used 107 dbqueries ... used 1.2285070419312 seconds Scheduled task complete: Cleanup of task logs (core\task\task_log_cleanup_task)