Manual liveliness disrupted when partitions change

Rule 15 · applies to the subscriber · Back to all rules

Breaks a guarantee. A partition change unmatches the pair, so manual liveliness assertions may not reach the reader and it can report the writer as lost.

If you set Liveliness = MANUAL_BY_TOPIC together with Partition names are set (non-empty)

Breaks a guarantee

• Settings involved: Partition and Liveliness
• What QoS Guard checks: [LIVENS = MANUAL] ∧ [PART.names ≠ ∅]

Example

A publisher asserts liveliness manually inside a partition. Moving partitions makes the subscriber briefly see the writer as not-alive.

How to fix it

Keep partition membership stable on manually-asserted-liveliness topics, or use AUTOMATIC liveliness.

Why this rule is flagged

What the DDS specification says

OMG DDS §	QoS policy	Standard statement
§2.2.3.13	PARTITION	A DataWriter and a DataReader must have a partition name in common to communicate. Failure to match partitions is not considered an incompatible QoS and does not trigger an OFFERED_INCOMPATIBLE_QOS or REQUESTED_INCOMPATIBLE_QOS status.
§2.2.3.11	LIVELINESS	The LIVELINESS policy controls the mechanism and lease duration used to determine whether a DataWriter is alive.

Rule 15 is derived from this interaction: if partition matching prevents the writer and reader from communicating, manual liveliness assertions are not exercised for that peer because the matched endpoint relationship is not formed.

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What the engine source code shows

Partition matching is checked during endpoint matching in both implementations. If the writer and reader partitions do not match, the endpoints are not matched, so manual liveliness is not exercised for that peer.

Fast DDS implementation evidence

// EDP.cpp: partition mismatch -> matching failure, not incompatible_qos
// Partition mismatch does not trigger status change.

if (!matched) // Different partitions
{
    reason.set(MatchingFailureMask::partitions);
}

return matched;

// pairingReader: only valid matches are registered
bool valid = valid_matching(&rdata, wdatait, no_match_reason, incompatible_qos);

if (valid)
{
    R->matched_writer_add(*wdatait);
}

Source: EDP.cpp lines 737-800 and 1061-1095.

Fast DDS compares writer and reader partitions during endpoint matching. If the partitions do not match, EDP::valid_matching() returns false with MatchingFailureMask::partitions, without setting PARTITION_QOS_POLICY_ID as an incompatible QoS. Because matched_writer_add() / matched_reader_add() are called only for valid matches, a partition mismatch silently prevents the matched peer from being formed.

Cyclone DDS implementation evidence

// q_qosmatch.c: partition compatibility check
if ((mask & QP_PARTITION) && !partitions_match_p(rd_qos, wr_qos))
{
    *reason = DDS_PARTITION_QOS_POLICY_ID;
    return false;
}

Source: q_qosmatch.c around the partition compatibility check.

For Rule 15, partition mismatch acts before liveliness monitoring: it removes the communicating peer rather than producing a liveliness event.

Item	Value
Dataset	Download CSV
Fixed QoS setting	None
Tested variable	PARTITION, LIVENS.kind
Tested values	PART ∈ {empty, A}, LIVENS.kind ∈ {AUTOMATIC, MANUAL_BY_TOPIC}
Rule-relevant case	PART = empty vs PART = A under the same LIVENS.kind
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 = 256 B

Engine	Tested setting	Observed behavior
Fast DDS 2.6.11 (Humble)	PART ∈ {empty, A}, LIVENS.kind ∈ {AUTOMATIC, MANUAL_BY_TOPIC}	PART = A matched and delivered; PART = empty did not match or deliver
Fast DDS 2.14.6 (Jazzy)	PART ∈ {empty, A}, LIVENS.kind ∈ {AUTOMATIC, MANUAL_BY_TOPIC}	PART = A matched and delivered; PART = empty did not match or deliver
Cyclone DDS 0.10.5	PART ∈ {empty, A}, LIVENS.kind ∈ {AUTOMATIC, MANUAL_BY_TOPIC}	PART = A matched and delivered; PART = empty did not match or deliver

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What you'll see when you run it

QoS Guard flags this as a functional conflict:

[FUNCTIONAL] [cmd_sub] [SUB] LIVENS=MANUAL_BY_TOPIC <-> PART.names≠Ø

At runtime a partition change unmatches the writer and reader, and a partition mismatch removes the peer rather than raising an incompatible-QoS event. While the pair is unmatched the writer's manual liveliness assertions cannot reach the reader, so the reader can report the writer as not-alive even though it is still running. The liveliness guarantee is broken by the partition transition rather than by a real writer failure.