7 Using the Engine Tier Cache

This chapter describes how to enable the engine tier cache for improved performance with SIP-aware load balancers:

• Overview of Engine Tier Caching

• Configuring Engine Tier Caching

• Monitoring and Tuning Cache Performance

Overview of Engine Tier Caching

The default Oracle Communications Converged Application Server configuration the engine tier cluster is stateless. A separate SIP data tier cluster manages call state data in one or more partitions, and engine tier servers fetch and write data in the SIP data tier as necessary. Engines can write call state data to multiple replicas in each partition to provide automatic failover should a SIP data tier replica going offline.

Converged Application Server also provides the option for engine tier servers to cache a portion of the call state data locally, as well as in the SIP data tier. When a local cache is used, an engine tier server first checks its local cache for existing call state data. If the cache contains the required data, and the local copy of the data is up-to-date (compared to the SIP data tier copy), the engine locks the call state in the SIP data tier but reads directly from its cache. This improves response time performance for the request, because the engine does not have to retrieve the call state data from a SIP data tier server.

The engine tier cache stores only the call state data that has been most recently used by engine tier servers. Call state data is moved into an engine's local cache as necessary in order to respond to client requests or to refresh out-of-date data. If the cache is full when a new call state must be written to the cache, the least-recently accessed call state entry is first removed from the cache. The size of the engine tier cache is not configurable.

Using a local cache is most beneficial when a SIP-aware load balancer manages requests to the engine tier cluster. With a SIP-aware load balancer, all of the requests for an established call are directed to the same engine tier server, which improves the effectiveness of the cache. If you do not use a SIP-aware load balancer, the effectiveness of the cache is limited, because subsequent requests for the same call may be distributed to different engine tier severs (having different cache contents).

Configuring Engine Tier Caching

Engine tier caching is enabled by default. To disable partial caching of call state data in the engine tier, specify the engine-call-state-cache-enabled element in sipserver.xml:

<engine-call-state-cache-enabled>false</engine-call-state-cache-enabled>

When enabled, the cache size is fixed at a maximum of 250 call states. The size of the engine tier cache is not configurable.

Monitoring and Tuning Cache Performance

SipPerformanceRuntime monitors the behavior of the engine tier cache. Table 7-1 describes the MBean attributes.

Table 7-1 SipPerformanceRuntime Attribute Summary

Attribute	Description
cacheRequests	Tracks the total number of requests for session data items.
cacheHits	The server increments this attribute each time a request for session data results in a version of that data being found in the engine tier server's local cache. Note that this counter is incremented even if the cached data is out-of-date and needs to be updated with data from the SIP data tier.
cacheValidHits	This attribute is incremented each time a request for session data is fully satisfied by a cached version of the data.

When enabled, the size of the cache is fixed at 250 call states. Because the cache consumes memory, you may need to modify the JVM settings used to run engine tier servers to meet your performance goals. Cached call states are maintained in the tenured store of the garbage collector. Try reducing the fixed "NewSize" value when the cache is enabled (for example, -XX:MaxNewSize=32m -XX:NewSize=32m). Note that the actual value depends on the call state size used by applications, as well as the size of the applications themselves.