Best way to invalidate a number of memcache keys using standard php libraries?

Question

I have a database with files which can be searched, browsed and have multiple copies on multiple servers.

I cache searches, browse pages and server locations (urls). Say

Answer 1

Having come accross the comment here, which explains the logic of evicting existing keys, I believe tags can be implemented reliable by the version flags approach mentioned in: PHP memcache design patterns

I actually implemented this logic once already, but discarded it as unreliable due to memcache eviction of elements before they expire. You can find my initial implementation here. I do however, believe this is a reliable tags pattern because:

• On cache object retrieval, the object is moved on top of the LRU stack
• All tags/flags are retrieved right after the cache object
• If a flag is evicted, any item containing this flag would have been evicted just before
• Incrementing a flag returns the new value in the same operation, avoiding write concurrency. If a second thread is incrementing the same flag before the cache object is written, it is by definition invalid already

Please correct me if I'm wrong! :-)