Bill: Mysql5.6 Cache Hit Ratio

MySQL Cache hit ratio, the online statement is different, below I say my view, everyone tap:

The total number of select queries equals Com_select (dead) + qcache_hits (hit) + Parse error query.

Let's take a look at the Com_select variable:

Mysql>Show Global Status like 'Com_select'; +---------------+-------+  |Variable_name|Value|  +---------------+-------+  |Com_select|  $    |  +---------------+-------+  

Com_select equals qcache_inserts (cache invalidation) + Qcache_not_cache (no cache) + Permission check error query.

Therefore, the query cache hit rate for MySQL ≈qcache_hits/(qcache_hits + com_select)

Query Cache variables:

Mysql>Show Global Status like 'qcache%'  +-------------------------+----------+  |Variable_name|Value|  +-------------------------+----------+  |Qcache_free_blocks| 1        |  |Qcache_free_memory| 18856920 |  |Qcache_hits| 3        |  |Qcache_inserts|  -       |  |Qcache_lowmem_prunes| 0        |  |Qcache_not_cached|  -       |  |Qcache_queries_in_cache| 0        |  |Qcache_total_blocks| 1        |  +-------------------------+----------+ 

So the query cache hit ratio ≈3/(3+46) = 6.12% in this example

Query cache variable Meaning:

Qcache_free_blocks	The number of memory blocks in the Query cache, which is still idle, is large, indicating that there may be fragmentation. FLUSH QUERY Cache organizes the fragments in the cache to get a free block.
Qcache_free_memory	The total amount of free memory in the cache.
Qcache_hits	The number of cache hits.
Qcache_inserts	The number of cache failures.
Qcache_lowmem_prunes	The number of times that the cache is out of memory and must be cleaned up to provide space for more queries. This number is best seen over a long period of time, and if the number is growing, it can mean that fragmentation is very serious, or that there is little memory. (The Free_blocks and free_memory above can tell you which is the case).
Qcache_not_cached	The number of queries that are not appropriate for caching, usually because these queries are not a SELECT statement and are not cached by the cache because of query_cache_type settings.
Qcache_queries_in_cache	The number of queries (and responses) currently cached.
Qcache_total_blocks	The number of blocks in the cache.

Bill: Mysql5.6 Cache Hit Ratio