I have installed Cacherouter with default engine APC = 256Mb, memory gone in 10 min,
when i switched to default db, i've got high load on mysql. It works well, but with 5G / hour traffic of output. So my bin logs grows very fast.
I would like to know, is there any politics for cache, or by default it's resourse assumed unlimited?
If it had something like LRU in mysql cache, i could control how much memory allocate for cache, be sured it will not overflowed.

And what timings for clear cahe i can use? I have set "min lifetime cache = 1 min" in admin/settings/performance, so I was surprised that APC is out of memory. Is there any more tweaks to reduce cache size?

Can I manually set expire=1 hour for cache_form in core?

<?php
//    includes/form.inc
function form_set_cache($form_build_id, $form, $form_state) {
  global $user;
  // 6 hours cache life time for forms should be plenty.
  $expire = 21600;
?>

It has the most size, about 140mb.

I choosed to use CacheRouter it works well, but I can't use it with mysql because of traffic and can't figure out what is the optimal size for APC.

Please, help.