Lifespan longer than the resource-limit buffer can ever hold
Rule 18 · applies to publishers and subscribers · Back to all rules
Wastes effort. The buffer fills and drops samples before the Lifespan expires, so the extra validity never takes effect.
- Settings involved: Resource Limits and Lifespan
- What QoS Guard checks:
[HIST.kind = KEEP_ALL] ∧ [LFSPAN.duration > RESLIM.mpi × PP]
Example
max_samples_per_instance 10 at a 20 ms period holds about 200 ms, but Lifespan is 2 s. Samples are evicted by capacity long before they expire.
How to fix it
Match Lifespan to the buffer capacity. Raise max_samples_per_instance or lower Lifespan.
Why this rule is flagged
What the DDS specification says
The DDS specification does not settle this case on its own, so the rule rests on direct measurement.
What the engine source code shows
This page grounds the rule in the measurement below rather than a separate source trace.
What the measurements show
| Item | Value |
|---|---|
| Dataset | Download CSV |
| Fixed QoS setting | HIST.kind = KEEP_ALL, RESLIM.mpi = 3, DURABL = TRANSIENT_LOCAL |
| Tested variable | LIFESPAN.duration |
| Tested values | LIFESPAN.duration ∈ {50 ms, 100 ms, 150 ms, 200 ms, 250 ms} |
| Rule boundary | RESLIM.mpi × PP = 3 × 50 ms = 150 ms |
| Rule-relevant case | LIFESPAN.duration > RESLIM.mpi × PP, i.e., LIFESPAN.duration ∈ {200 ms, 250 ms} |
| Tested engines / versions | Fast DDS 2.14.6 (Jazzy), Cyclone DDS 0.10.5 |
| Network setting | RTT ∈ {1 ms, 50 ms}, loss ∈ {0%, 20%}, PP = 50 ms, message size = 1024 B |
| Primary metric | late_join_recovered |
| Supplementary metric | delivery_ratio |
Measurement result
Main late-join recovery view
The heatmaps show late-join recovery as LIFESPAN.duration crosses the RESLIM.mpi × PP = 150 ms window.
Supplementary delivery-ratio view
The supplementary heatmaps show average delivery ratio under the same settings; the primary Rule 18 evidence is the late-join recovery view above.