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 integer64u: 64-bit unsigned integer32u32u: Two 32-bit unsigned integers separated by a colonString: 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.