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LIFESPAN

Controls how long a sample published by a Publisher remains valid.

What it controls

The expiration duration for samples in the Writer HistoryCache. Expired samples are not delivered to new or existing Readers.

Key settings

Field Default Mutability
duration infinity Can be changed at runtime

Compatibility role

Timing and cache — limits how long samples remain deliverable. Interacts with deadline period, history depth, resource limits, durability, and reliable delivery windows.

When this conflicts

Lifespan takes part in the following QoS Guard rules. Each links to a full explanation with an example and a fix.

Finite lifespan expires the history that durability should replay with DurabilityBreaks a guarantee Lifespan shorter than the deadline period with DeadlineBreaks a guarantee Lifespan longer than the history window can ever hold with HistoryWastes resources Lifespan longer than the resource-limit buffer can ever hold with Resource LimitsWastes resources Lifespan expires samples before reliable retransmission finishes with ReliabilityBreaks a guarantee

Example

The LFSPAN QoS can be used to prevent robots from retaining outdated samples unnecessarily. For data such as position or battery level, where only the last few seconds matter, setting the duration accordingly ensures that the Publisher's HistoryCache stores only the most recent samples, with older ones automatically deleted to conserve memory. In contrast, for data such as command logs, where long-term delivery is more important than freshness, it is preferable to set duration to infinity and rely on other QoS policies to ensure reliability.