F5 RAM cache Utilization Test

A RAM cache is a cache of HTTP objects stored in the BIG-IP systems random-access memory (RAM) that subsequent connections can reuse to reduce the amount of load on the backend servers. The RAM cache feature provides the ability to reduce the traffic load to backend servers. This ability is useful if an object on a site is under high demand, if the site has a large quantity of static content, or if the objects on the site are compressed. For compressible data, the RAM cache can store data for clients that can accept compressed data. When used in conjunction with the compression feature on the BIG-IP system, the RAM cache takes stress off the BIG-IP system and the content servers. If the RAM cache is not adequately sized or is not able to cater to the requests, then the backend servers may be overloaded with requests defying the very purpose of the cache. Therefore, it is necessary to constantly keep track of the cache. The F5 RAM cache Utilization test helps administrators in this regard!

Using this test, administrators can figure out the average percentage of data that was serviced by the RAM cache, the percentage of bytes that were serviced from the RAM cache etc. In addition, this test also helps administrators identify the percentage of data that was removed from the RAM cache.

Target of the test : A Big-IP/F5 Local Traffic Manager

Agent deploying the test : A remote agent

Outputs of the test : One set of results for the target F5 Local Traffic Manager being monitored

Configurable parameters for the test
Parameter Description

Test Period

How often should the test be executed

Host

The IP address of the traffic manager

Port

The port number on which the traffic manager is listening. By default, this is NULL.

Measurements made by the test
Measurement Description Measurement Unit Interpretation

Cache hit ratio

Indicates the percentage of data that was serviced from the RAM cache.

Percent

Ideally, the value of this measure should be high. A low value indicates that many read requests are serviced by direct disk accesses, which is a more expensive operation in terms of processing overheads.

Average cache hit ratio

Indicates the average percentage of data that was serviced from the RAM cache.

Percent

A high value is desired for this measure.  

Cache byte ratio

Indicates the percentage of bytes that were serviced from the RAM cache.

Percent

 

Average byte ratio

Indicates the average percentage of bytes that were cached in the RAM cache.

Percent

 

Cache eviction ratio

Indicates the percentage of data that was removed from the RAM cache.

Percent

A low value is desired for this measure. A higher value of this measure may be an indication of outdated entries in the cache which should be evicted from the cache to accommodate new cache entries.

Average Cache eviction rate

Indicates the average percentage of data that was removed from the RAM cache.

Percent