15.6.4.1. memcached General Statistics

The output of the general statistics provides an overview of the performance and use of the memcached instance. The statistics returned by the command and their meaning is shown in the following table.

The following terms are used to define the value type for each statistics value:

32u: 32-bit unsigned integer
64u: 64-bit unsigned integer
32u:32u: Two 32-bit unsigned integers separated by a colon
String: Character string

Statistic	Data type	Description	Version
`pid`	32u	Process ID of the memcached instance.
`uptime`	32u	Uptime (in seconds) for this memcached instance.
`time`	32u	Current time (as epoch).
`version`	string	Version string of this instance.
`pointer_size`	string	Size of pointers for this host specified in bits (32 or 64).
`rusage_user`	32u:32u	Total user time for this instance (seconds:microseconds).
`rusage_system`	32u:32u	Total system time for this instance (seconds:microseconds).
`curr_items`	32u	Current number of items stored by this instance.
`total_items`	32u	Total number of items stored during the life of this instance.
`bytes`	64u	Current number of bytes used by this server to store items.
`curr_connections`	32u	Current number of open connections.
`total_connections`	32u	Total number of connections opened since the server started running.
`connection_structures`	32u	Number of connection structures allocated by the server.
`cmd_get`	64u	Total number of retrieval requests (`get` operations).
`cmd_set`	64u	Total number of storage requests (`set` operations).
`get_hits`	64u	Number of keys that have been requested and found present.
`get_misses`	64u	Number of items that have been requested and not found.
`delete_hits`	64u	Number of keys that have been deleted and found present.	1.3.x
`delete_misses`	64u	Number of items that have been delete and not found.	1.3.x
`incr_hits`	64u	Number of keys that have been incremented and found present.	1.3.x
`incr_misses`	64u	Number of items that have been incremented and not found.	1.3.x
`decr_hits`	64u	Number of keys that have been decremented and found present.	1.3.x
`decr_misses`	64u	Number of items that have been decremented and not found.	1.3.x
`cas_hits`	64u	Number of keys that have been compared and swapped and found present.	1.3.x
`cas_misses`	64u	Number of items that have been compared and swapped and not found.	1.3.x
`cas_badvalue`	64u	Number of keys that have been compared and swapped, but the comparison (original) value did not match the supplied value.	1.3.x
`evictions`	64u	Number of valid items removed from cache to free memory for new items.
`bytes_read`	64u	Total number of bytes read by this server from network.
`bytes_written`	64u	Total number of bytes sent by this server to network.
`limit_maxbytes`	32u	Number of bytes this server is permitted to use for storage.
`threads`	32u	Number of worker threads requested.
`conn_yields`	64u	Number of yields for connections (related to the `-R`option).	1.4.0

The most useful statistics from those given here are the number of cache hits, misses, and evictions.

A large number of get_misses may just be an indication that the cache is still being populated with information. The number should, over time, decrease in comparison to the number of cache get_hits. If, however, you have a large number of cache misses compared to cache hits after an extended period of execution, it may be an indication that the size of the cache is too small and you either need to increase the total memory size, or increase the number of the memcached instances to improve the hit ratio.

A large number of evictions from the cache, particularly in comparison to the number of items stored is a sign that your cache is too small to hold the amount of information that you regularly want to keep cached. Instead of items being retained in the cache, items are being evicted to make way for new items keeping the turnover of items in the cache high, reducing the efficiency of the cache.