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The Distributed Cache service, which is built on Windows Server AppFabric Cache, is set to run in a collocated mode on all SharePoint 2013 Servers by default. It's essential for maintaining the large amounts of information on your SharePoint Server, ensuring that the information is fresh and readily available for the end user.

Caching functionalities, provided by the Distributed Cache service, enable web applications deployed on SharePoint to quickly retrieve data without any dependency on databases stored in SQL Server, as everything is stored in memory.

Any SharePoint server in the farm running the Distributed Cache service is known as a cache host. Cache size is the memory allocated to the Distributed Cache service on the cache host.

At any given point in time, sufficient memory resources should be available to the Distributed cache service to ensure optimum cache usage and to assure SharePoint users of a satisfactory experience with their web applications. In the absence of adequate memory, cache lookups will be delayed or even missed, thus affecting overall SharePoint performance and adversely impacting the health of user interactions with the web applications.

It is hence imperative that administrators keep an eye on the usage of the cache service by each dependent web application, rapidly detect unexpected slowness in cache reads and writes, capture cache misses, and figure out if such anomalies are owing to the bad size of the Distributed cache service. This is what the SPDcTest test help administrators do!

This test queries the SharePoint usage database and retrieves metrics revealing how each web application uses the distributed cache, from it. The metrics so collected reveal the following:

This way, the test brings cache usage and sizing irregularities to light, pinpoints the exact web application that is being impacted by these abnormalities, and thus prompts administrators to right-size the cache to ensure peak application performance.

Note that this test will run only if a SharePoint Usage and Health Service application is created and is configured to collect usage and health data. To know how to create and configure this application, Click here.

Output of the test : One set of results for each web application in the monitored SharePoint server

Measurement	Description	Measurement Unit	Interpretation
Distributed_cache_reads	Indicates the number of cache reads performed by this web application.	Number
cache_reads_duration	Indicates the average time taken by this web application to read from the cache.	Msecs	A low value is desired for this measure. A consistent increase in the value of this measure could indicate a reading bottleneck. One of the reasons for reading delays is insufficient memory for the cache on the host. You may want to right-size the cache to make sure that your requests are serviced quickly and efficiently. Reading delays can also occur if the cache is overloaded with read requests or too much data is to be read. Whenever this measure registers an abnormally high value for a web application, look up the value reported by the Distributed_cache_reads and cache_reads_size measures for the same web application to determine whether/not the slowness can be attributed to the count and size of the reads.
cache_reads_size	Indicates how many kilobytes of data, on an average, are read from the cache by this web application.	KB
Distributed_cache_writes	Indicates the number of writes to the cache by this web application.	Number
cache_writes_duration	Indicates the average time taken by this web application to write to the cache.	Number	A low value is desired for this measure. A consistent increase in the value of this measure could indicate a writing bottleneck. One of the reasons for writing delays is insufficient memory for the cache. You may want to right-size the cache to make sure that your requests are serviced quickly and efficiently. Writing delays can also occur if the web application is overloading the cache with write requests or too much data is to be written. Whenever this measure registers an abnormally high value for a web application, look up the value reported by the Distributed_cache_writes and cache_writes_size measure for the same application to determine whether/not the slowness can be attributed to the unusually high number and size of the writes.
cache_writes_size	Indicates how many kilobytes of data, on an average, are written to the cache by this web application.	KB
Distributed_cache_misses	Indicates the number of requests from this web application that were not serviced by the cache.	Number	Ideally, the value of this measure should be 0. If on the other hand, this measure value is close to the value of the Objects requested measure, it is a cause for serious concern, as it implies that almost all objects requested were not found in the cache. Under such circumstances, use the detailed diagnoss of this measure to know which web site addresses could not be found in the cache. One of the reasons for a high number of misses could be insufficient memory allocation to the cache service. In such a situation, you may want to increase the cache size by adding more memory.
Distributed_cache_hits	Indicates the number of requests from this web application that were successfully served by this cache.	Number	Ideally, the value of this measure should be the same as the value of the cached_objects_requested measure. If not, check whether the cache has enough memory, and if required, add more memory to it.
Distributed_cache_fail	Indicates the number of cache failures experienced by this web application.	Number	Ideally, the value of this measure should be 0. If this measure reports a non-zero value, then use the detailed diagnosis of this measure to know which web site addresses were being looked up in the cache when the failures occurred.
cached_objects_requested	Indicates the number of objects requested by this web application.	Number	&nbap;