16.6.4.1 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:

StatisticData typeDescriptionVersion
pid32uProcess ID of the memcached instance. 
uptime32uUptime (in seconds) for this memcached instance. 
time32uCurrent time (as epoch). 
versionstringVersion string of this instance. 
pointer_sizestringSize of pointers for this host specified in bits (32 or 64). 
rusage_user32u:32uTotal user time for this instance (seconds:microseconds). 
rusage_system32u:32uTotal system time for this instance (seconds:microseconds). 
curr_items32uCurrent number of items stored by this instance. 
total_items32uTotal number of items stored during the life of this instance. 
bytes64uCurrent number of bytes used by this server to store items. 
curr_connections32uCurrent number of open connections. 
total_connections32uTotal number of connections opened since the server started running. 
connection_structures32uNumber of connection structures allocated by the server. 
cmd_get64uTotal number of retrieval requests (get operations). 
cmd_set64uTotal number of storage requests (set operations). 
get_hits64uNumber of keys that have been requested and found present. 
get_misses64uNumber of items that have been requested and not found. 
delete_hits64uNumber of keys that have been deleted and found present.1.3.x
delete_misses64uNumber of items that have been delete and not found.1.3.x
incr_hits64uNumber of keys that have been incremented and found present.1.3.x
incr_misses64uNumber of items that have been incremented and not found.1.3.x
decr_hits64uNumber of keys that have been decremented and found present.1.3.x
decr_misses64uNumber of items that have been decremented and not found.1.3.x
cas_hits64uNumber of keys that have been compared and swapped and found present.1.3.x
cas_misses64uNumber of items that have been compared and swapped and not found.1.3.x
cas_badvalue64uNumber of keys that have been compared and swapped, but the comparison (original) value did not match the supplied value.1.3.x
evictions64uNumber of valid items removed from cache to free memory for new items. 
bytes_read64uTotal number of bytes read by this server from network. 
bytes_written64uTotal number of bytes sent by this server to network. 
limit_maxbytes32uNumber of bytes this server is permitted to use for storage. 
threads32uNumber of worker threads requested. 
conn_yields64uNumber 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.