Description:
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as far as i can see in the hit-stats it seems that mysqlnd_qc has not a common cache for a query - each httpd-worker has it's own non-shared cache

this is a design mistake

1. you do not benfit from the cache at all if there a 400 workers
2. you are wasting memory by have 400 copies of the same result

on high traffic websites mysqlnd_qc would be a hughe improvement with a cache time of 2-4 seconds for conent-queries when you have hundrets of requests per second, but if you have some hundret active workers with a non-shared cache this does not help much

the cache should work like APC with a mmap'ed common storage