Client doesn't ran Cron for >6 months. So in database, we had large tables. I have cleared tables accesslog, cache_*, watchdog, flood manually in MySQL.
After that, running Cron runs forever. Especially system_cron(). What part of that function can cause this? It seems that probably mysql is eating RAM, but I'm not sure.
system_cron() touches following tables - cache_* (empty), flood(empty), batch(1 row), queue(159 rows), file_managed(18,163 rows).
Maybe something is wrong with file_managed?