[TYPO3-core] FYI72: #15497: [Caching framework] Remove tagIndex from memcached and apc backend

[Vladimir Podkovanov]

Hi Christian,

Christian Kuhn wrote:
> Numbers:
> Performance tests of memcached backend show that the backend speeds up 
> between 10 to 100% by removing the tagIndex. As an example, attached 
> images show a test which set()'s a raising number of cache entries with 
> a single attached tag to the backend. More numbers can be generated with 
> ext:enetcacheanalytics (forge) in v4.
> 
> Notes:
> - Memcache is a simple key-value store and not designed to store 
> structures of multiple related entries. Our implementation is a misuse, 
> which leads to corrupt caches if memcache evicts entries from cache 
> (because it needs space for new elements), or if single servers fail in 
> a multi server environment.

Nice on performance improvement!

Regarding misuse of memcached - I saw other 3rd party libraries for 
tagging with memcached which are free from data integrity corruption in 
case of entries evicts (in such case all dependent data invalidated too 
and result is consistent). I'm not familiar with current memcached 
backend in TYPO3. Is it for sure that current implementation is 
vulnerable to entries evicts? In such case it is not suitable for 
production.
-- 
-rgds-
Vladimir