HANA Cache Test

A cache that is right-sized and well-used can significantly boost database server performance! A cache is said to be effectively utilized only if it is able to service the maximum number of requests to the database; this greatly reduces direct disk accesses and related overheads, and thus improves database performance. On the contrary, ineffective cache usage can be the key contributor to a slowdown or degradation in server performance, as it increases disk accesses. To understand how the database caches are utilized and to promptly capture abnormalities in cache usage, administrators have to continuously monitor the size and usage of each of the database caches. The HANA Cache test helps administrators in this regard. This test monitors each cache of the SAP HANA database server and reports its usage – both in terms of size and its request serving ability. In the process, the test proactively alerts administrators to the under-utilization and improper size of the cache, and helps them quickly initiate corrective measures.

Target of the test : A SAP HANA Database Server

Agent deploying the test : A remote agent

Outputs of the test : One set of results for every cache of the SAP HANA database server being monitored.

Configurable parameters for the test

Parameter	Description
Test period	How often should the test be executed
Host	The host for which the test is to be configured.
Port	The port number at which the specified Host listens to. By default, this will be 30015.
User	In order to monitor a SAP HANA database server, a special database user account with Monitoring privileges has to be created in every SAP HANA database instance that requires monitoring. The syntax of the script that is used for user creation is discussed in How to Monitor SAP HANA Database Server Using eG Enterprise?. The name of such a user has to be specified here.
Password	Enter the password of the specified User.
Confirm Password	Confirm the password by retyping it here.
IsPassive	If the value chosen for this parameter is Yes, then the SAP HANA database server under consideration is a passive server in a SAP HANA cluster. No alerts will be generated if the server is not running. Measures will be reported as “Not applicable” by the agent if the server is not up.

Measurements made by the test

Measurement	description	Measurement Unit	Interpretation
Total Size	Indicates the total size of this cache.	MB
Used Size	Indicates the space in the cache that is currently in use.	MB	Ideally, the value of this measure should be low. A high value or a consistent rise in the value is a sign that the cache is about to run out of space. If a cache does not have adequate space, it cannot hold additional entries, and hence cannot service requests properly. You may hence have to allocate more space to the cache or free-up space in the cache to accommodate more entries.
Entries	Indicates the number of entries i.e., requests or transactions that are available for retrieval from this cache.	Number	Ideally, the value of this measure should be high.
Inserts	Indicates the number of INSERT entries that can be retrieved from this cache based on a received request.	Number
Invalidates	Indicates the number of INVALIDATE entries that can be retrieved from this cache based on a received request.	Number
Hits	Indicates the number of times this cache was hit for an entry without having to read from the disk during the last measurement period.	Number	A high value is desired for this measure. A low value or a consistent drop in this value is a cause for concern, as it indicates ineffective cache usage. This means high disk accesses, and poor server performance. One of the common reasons for bad cache usage is improper cache size. A cache that does not have sufficient space to accommodate entries will not be able to service requests effectively.  You may hence have to allocate more space to the cache or free-up space in the cache to accommodate more entries.
Misses	Indicates the number of times this cache was missed for an entry during the last measurement period.	Number	A low value is desired for this measure. A high value or a consistent increase in this value is a cause for concern, as it indicates ineffective cache usage. This means high disk accesses and poor server performance. One of the common reasons for bad cache usage is improper cache size. A cache that does not have sufficient space to accommodate entries will not be able to service requests effectively.  You may hence have to allocate more space to the cache or free-up space in the cache to accommodate more entries.