[support] When are Caches Cleared?

[Fred Jones]

>> Question is when does it expire? I see there is a minimum and mine is
>> set to NONE. I *think* what I am asking is about the maximum.
>
> That would depend on the "cache_flush_$table" variable and the
> cache_lifetime variable and whether or not the cache is deemed
> CACHE_PERMANENT (a.k.a. expire == 0).  See
> http://api.drupal.org/api/function/cache_get/6 for more information.
> CACHE_PERMANENT should only be used for things like variables data and
> the theme_registry.  'cache_lifetime' is the variable for the minimum.
>
> Tracing through it, maybe there is a bug but I don't know it to be.  I
> am sure that if "cache_flush_$table" isn't set that the cache will never
> be deleted unless cache_clear_all is called with a "wildcard".

Yes, that's how it appears. The only DELETE I see there is inside of:

 if ($cache_flush &&

and I checked my site and it has no cache_flush_* entries in the
variable table. I checked a few sites actually and none of them appear
to have that.

So are we back to my sneaking suspicion that a 'regular' site has no
maximum expiration for cache? Seems that's what you wrote above also.

Thanks.