This documentation space contains information about PATROL Agents when deployed in a BMC Helix Operations Management environment. If you are a TrueSight Operations Management user, see PATROL Agent 21.02.

Managing the PATROL event cache

PATROL allows you to manage the Event Cache by size or by number of events per object. PATROL uses this variable to determine how to manage event cache size, and if by event number, how many events it must retain per object.

Setting the cache size

The /AgentSetup/pemCacheSize configuration variable determines the size in bytes of the cache used by the agent for event management.

Format and type of data

Numeric, bytes

Default value


Minimum and maximum

10, 20480


/AgentSetup/pemEvMemRetention determines whether this variable has any effect. If the value of pemEvMemRetention is greater than zero, the PATROL Agent ignores the value of this variable.


A larger cache size improves the performance of the agent but consumes more memory.

To determine the value to use, estimate 200 bytes per event.


An event is triggered. The agent gets the object of the incoming event and reads the number of events stored for that object. If the number of events is less than pemEvMemRetention, the agent saves the incoming event in the cache. If the number is greater than or equal to the variable, the agent transfers the oldest event to the log and saves the new event in the cache. When the cache fills up, the agent increases the cache size by half of its current size. The agent bases the cache's initial size on pemCacheSize.

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