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Best-effort delivery with exclusive ownership

Rule 4 · applies to publishers and subscribers · Back to all rules

Breaks a guarantee, and behavior depends on the DDS version. Fast DDS 2.6 (Humble) rejects it at creation, while Fast DDS 2.14 and Cyclone DDS accept it and fail over slowly.

If you set Reliability = BEST_EFFORT together with Ownership = EXCLUSIVE
Breaks a guarantee
  • Settings involved: Reliability and Ownership
  • What QoS Guard checks: [OWNST = EXCLUSIVE] ∧ [RELIAB = BEST_EFFORT]

Example

Two redundant sensor publishers use EXCLUSIVE ownership over best-effort. On Humble the reader is rejected. On Jazzy it runs, but failover is slow and can drop samples.

How to fix it

Use RELIABLE with EXCLUSIVE ownership so the strongest writer's samples are delivered dependably during failover.

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 the engine's implementation and direct measurement.

What the engine source code shows

Fast DDS 2.6.11 rejects BEST_EFFORT with EXCLUSIVE ownership at QoS validation; Fast DDS 2.14.6 accepts the profile.

Fast DDS implementation evidence

// Only the FastDDS code contains code that checks this rule.
if (m_reliability.kind == BEST_EFFORT_RELIABILITY_QOS && m_ownership.kind == EXCLUSIVE_OWNERSHIP_QOS)
{
    logError(RTPS_QOS_CHECK, "BEST_EFFORT incompatible with EXCLUSIVE ownership");
    return false;
}
return true;

What the measurements show

Item Value
Dataset Download CSV
Fixed QoS setting None
Tested variable RELIAB.kind, OWNST.kind
Tested values RELIAB ∈ {BEST_EFFORT, RELIABLE}, OWNST ∈ {SHARED, EXCLUSIVE}
Rule-relevant case RELIAB = BEST_EFFORT, OWNST = EXCLUSIVE
Tested engines / versions Fast DDS 2.6.11 (Humble), Fast DDS 2.14.6 (Jazzy), Cyclone DDS 0.10.5
Network setting RTT = 1 ms, loss = 0%, PP = 50 ms, message size = 1024 B
Engine Tested setting Observed behavior
Fast DDS 2.6.11 (Humble) RELIAB = BEST_EFFORT, OWNST = EXCLUSIVE Profile rejected at creation time
Fast DDS 2.14.6 (Jazzy) RELIAB = BEST_EFFORT, OWNST = EXCLUSIVE Profile accepted, matched, and delivered
Cyclone DDS 0.10.5 RELIAB = BEST_EFFORT, OWNST = EXCLUSIVE Profile accepted, matched, and delivered

Rule 4 Humble acceptance heatmap

The Humble validation data shows that Fast DDS 2.6.11 rejects EXCLUSIVE + BEST_EFFORT at profile creation time, while Cyclone DDS 0.10.5 accepts and matches the same QoS combination.