Question about percona Query Cache Enhancements

Read your document,you said the Percona Server disabling the cache completely.
I want to ask in the standard mysql version,when we set query_cache_type=0,what happens?
Still lock,but check query_cache_type=0,and return immediately?The lock is not disable completely and make some cpu consume?


Should be written as:

The definition of immediately if you do something 1000-3000 times a second can be after a proportionally very long time ;).

/* Testing ‘query_cache_size’ without a lock here is safe: the thing we may loose is that the query won’t be served from cache, but we save on mutex locking in the case when query cache is disabled. See also a note on double-check locking usage above. */ if (is_disabled() || thd->locked_tables_mode || thd->variables.query_cache_type == 0 || query_cache_size == 0) goto err;

I read the code,I find the check section is same and don’t find anything different with the standard mysql version.