rules scheduler performance I use drupal 6 with rules. I have more than 200 scheduled tasks (updating node's field)waiting to be executed at one time. Do I need to worry about server crash or is there some kind of queue implemented in scheduler? Thank you.
You need the Ultimate Cron module. It is an advanced system for managing scheduled tasks. You can set rules and custom schedules for every single task. Can be found here:

https://www.drupal.org/project/ultimate_cron