fileCache seems to expire even though I have it set to 0 I am using the fileCache command in a custom plugin. I've set it to never expire so that I can provide a special link to our client to force a refresh.

Problem is, the cache seems to be killing itself off. On one day I can see record of it regenerating three separate times, so it is 

$craft-&gt;fileCache-&gt;add($cacheKey, $dataToAddToCache, $cacheExpire);
$craft-&gt;fileCache-&gt;add('my-hardcoded-key', 'string of data', 0);


So basically I am doing this.

if (NEED_TO_REGEN) {
   $craft-&gt;fileCache-&gt;delete($cacheKey);
}
$a_cacheVal = $craft-&gt;fileCache-&gt;get($cacheKey);
if (empty($a_cacheVal)) {
    //use the cached data
} else {
   $craft-&gt;fileCache-&gt;add($cacheKey, $dataToAddToCache, $cacheExpire);
}


Does admin modification of resources affect fileCache at all (updating an entry wouldn't kill of my plugin fileCache would it?) The admins is not doing a full Clear Cache inside settings or anything. So why would this particular cache be regenerating frequently (multiple times per day in some case)?
You should be using craft()-&gt;cache with the cacheMethod config setting set to file (which it is by default) instead of craft()-&gt;fileCache.  The latter is deprecated and won't work in Craft 3.

Yii does have garbage collection on cache, and by default an item has a 0.01% change of being purged from cache regardless of expiry time.

If you think you're not being garbage collected, you can check the file modified time of the files in craft/storage/runtime/cache.  If you explicitly pass in 0 as an expiration time, Yii will set the file's modification date to a year out.