Metrics for Memcached - Amazon ElastiCache

Metrics for Memcached

The AWS/ElastiCache namespace includes the following Memcached metrics.

The AWS/ElastiCache namespace includes the following metrics that are derived from the Memcached stats command. Each metric is calculated at the cache node level.

See also

Metric Description Unit
BytesReadIntoMemcached The number of bytes that have been read from the network by the cache node. Bytes
BytesUsedForCacheItems The number of bytes used to store cache items. Bytes
BytesWrittenOutFromMemcached The number of bytes that have been written to the network by the cache node. Bytes
CasBadval The number of CAS (check and set) requests the cache has received where the Cas value did not match the Cas value stored. Count
CasHits The number of Cas requests the cache has received where the requested key was found and the Cas value matched. Count
CasMisses

The number of Cas requests the cache has received where the key requested was not found.

Count
CmdFlush The number of flush commands the cache has received. Count
CmdGet The number of get commands the cache has received. Count
CmdSet The number of set commands the cache has received. Count
CurrConnections

A count of the number of connections connected to the cache at an instant in time. ElastiCache uses 2 to 3 of the connections to monitor the cluster.

In addition to the above, memcached creates a number of internal connections equal to twice the threads used for the node type. The thread count for the various node types can be see in the Nodetype Specific Parameters of the applicable Parameter Group.

The total connections is the sum of client connections, the connections for monitoring and the internal connections mentioned above.

 Count
CurrItems A count of the number of items currently stored in the cache. Count
DecrHits The number of decrement requests the cache has received where the requested key was found. Count
DecrMisses The number of decrement requests the cache has received where the requested key was not found. Count
DeleteHits The number of delete requests the cache has received where the requested key was found. Count
DeleteMisses The number of delete requests the cache has received where the requested key was not found. Count
Evictions The number of non-expired items the cache evicted to allow space for new writes. Count
GetHits The number of get requests the cache has received where the key requested was found. Count
GetMisses The number of get requests the cache has received where the key requested was not found. Count
IncrHits The number of increment requests the cache has received where the key requested was found. Count
IncrMisses The number of increment requests the cache has received where the key requested was not found. Count
Reclaimed The number of expired items the cache evicted to allow space for new writes. Count

For Memcached 1.4.14, the following additional metrics are provided.

Metric Description Unit
BytesUsedForHash The number of bytes currently used by hash tables. Bytes
CmdConfigGet The cumulative number of config get requests. Count
CmdConfigSet The cumulative number of config set requests. Count
CmdTouch The cumulative number of touch requests. Count
CurrConfig The current number of configurations stored. Count
EvictedUnfetched The number of valid items evicted from the least recently used cache (LRU) which were never touched after being set. Count
ExpiredUnfetched The number of expired items reclaimed from the LRU which were never touched after being set. Count
SlabsMoved The total number of slab pages that have been moved. Count
TouchHits The number of keys that have been touched and were given a new expiration time. Count
TouchMisses The number of items that have been touched, but were not found. Count

The AWS/ElastiCache namespace includes the following calculated cache-level metrics.

Metric Description Unit
NewConnections The number of new connections the cache has received. This is derived from the memcached total_connections statistic by recording the change in total_connections across a period of time. This will always be at least 1, due to a connection reserved for a ElastiCache. Count
NewItems The number of new items the cache has stored. This is derived from the memcached total_items statistic by recording the change in total_items across a period of time. Count
UnusedMemory

The amount of memory not used by data. This is derived from the Memcached statistics limit_maxbytes and bytes by subtracting bytes from limit_maxbytes.

Because Memcached overhead uses memory in addition to that used by data, UnusedMemory should not be considered to be the amount of memory available for additional data. You may experience evictions even though you still have some unused memory.

For more detailed information, see Memcached item memory usage.

 Bytes