When should I increase SystemTopicsPriority above the default value of 1?

Increase this value to 2 if your application relies heavily on system events (like eviction or expiration notifications). This ensures critical system-level cache events are processed with higher preference than standard published messages, maintaining operational continuity.

What is the impact of setting a low PubSubClientInactivityTimeout?

Setting a lower timeout (near the 30s minimum) is ideal for environments like Docker or Kubernetes. It enables faster cleanup of inactive connections by quickly disconnecting inactive clients, thereby reducing memory overhead and preventing the accumulation of undelivered messages.

Do NCache Pub/Sub configuration settings apply per-cache or server-wide?

These settings are server-wide. Configuration changes made to the NCache Service file affect the global Pub/Sub subsystem behavior for all caches running on that node. For consistent cluster behavior, ensure these values are synchronized across all servers.

Pub/Sub Configuration

This page describes server-side configuration settings for NCache Pub/Sub messaging that control system topic priority and client inactivity handling. By prioritizing internal system events over user-published messages and automatically disconnecting inactive subscribers after a defined timeout, these settings help prevent message backlogs, ensure fair and timely event processing, and optimize resource utilization.

System Topic Priority

The SystemTopicsPriority specifies the priority level assigned to system topics used by the cache.

<add key="NCacheServer.SystemTopicsPriority" value="1"/>

System topics are used for events raised by the system, such as item-level or general-level events. By default, the priority is set to 1, which represents a normal priority. If system events are more important than the published messages, you can increase the value to 2. Conversely, if published messages have higher priority, you can lower the value to 0. This configuration adjustment is only required when the same cache instance is used for both events and Pub/Sub messaging.

Pub/Sub Client Inactivity Timeout

The PubSubClientInactivityTimeout defines the time duration (in seconds) after which inactive clients are automatically disconnected from the system. A client is considered inactive when the time elapsed since its last activity (sending or receiving data) exceeds the configured timeout value. The default value is 120 seconds, and the minimum configurable limit is 30 seconds.

<add key="NCacheServer.PubSubClientInactivityTimeout" value="120" />

This client inactivity timeout is particularly useful in scenarios where a large number of clients connect to the cache for short time periods. Automatically removing inactive clients helps the Pub/Sub system reduce the processing overhead associated with assigning messages to such clients. If messages are assigned to inactive clients, they may remain in the cache longer before the issue is detected. As the number of inactive clients increases, the number of unprocessed (assigned but undelivered) messages also grows, leading to potential delays and inefficiencies in message delivery.

Pub/Sub Configuration

System Topic Priority

Pub/Sub Client Inactivity Timeout

See Also

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