QoS Advisor

The QoS Advisor automatically detects DDS/RTPS misconfigurations and QoS policy issues. It analyzes traffic patterns and reports problems with actionable recommendations.

Overview

Access the QoS Advisor via View → QoS Advisor or press Ctrl+Q.

The advisor runs 15 detection rules covering:

• QoS compatibility issues between publishers and subscribers
• Resource exhaustion warnings
• Timing violations
• Type consistency problems

Detection Rules

Core QoS Rules (5)

Rule	Description	Severity
ReliabilityMismatch	Publisher BEST_EFFORT but subscriber expects RELIABLE	High
DurabilityMismatch	Durability levels incompatible (e.g., VOLATILE vs TRANSIENT_LOCAL)	High
HistoryDepthMismatch	History depth too small for subscriber consumption rate	Medium
DeadlineViolation	Messages not arriving within Deadline QoS period	High
LifespanExpired	Messages expiring before delivery (Lifespan QoS)	Medium

Extended QoS Rules (10)

Rule	Description	Severity
OwnershipConflict	Multiple writers with EXCLUSIVE ownership on same topic	High
PartitionMismatch	Publisher and subscriber in different partitions	Medium
ContentFilterInefficient	Content filter passing >80% of messages (wasted CPU)	Low
LatencyBudgetExceeded	End-to-end latency exceeds LatencyBudget QoS	Medium-High
TransportPriorityInversion	Low-priority traffic blocking high-priority	High
ResourceLimitsNearMax	Approaching max_samples or history depth limits	Critical
LivelinessTimeout	Writer liveliness lease expired (potential crash)	Critical
PresentationCoherenceViolation	Coherent updates received out of order	Medium
DestinationOrderViolation	Messages delivered out of order	Medium
TypeConsistencyWarning	Potential type mismatch between publisher/subscriber	High

Rule Details

ReliabilityMismatch

Problem: A subscriber configured for RELIABLE is connected to a publisher using BEST_EFFORT.

Symptoms:

• Missing messages
• Gaps in sequence numbers
• Subscriber reports data loss

Detection: Compares QoS hashes in discovery data.

Fix:

// Publisher side - match subscriber's reliability
DataWriterQos qos;
qos.reliability().kind = RELIABLE_RELIABILITY_QOS;

---

DurabilityMismatch

Problem: Durability levels are incompatible (e.g., subscriber expects TRANSIENT_LOCAL but publisher is VOLATILE).

Symptoms:

• Late-joining subscribers miss historical data
• Inconsistent state across nodes

Detection: Analyzes Durability QoS in endpoint discovery.

Fix:

// Ensure publisher durability >= subscriber durability
DataWriterQos qos;
qos.durability().kind = TRANSIENT_LOCAL_DURABILITY_QOS;

---

OwnershipConflict

Problem: Multiple writers claim EXCLUSIVE ownership on the same topic/instance.

Symptoms:

• Only highest-strength writer's data is delivered
• Confusing behavior during failover

Detection: Counts writers with ownership.kind = EXCLUSIVE per topic.

Fix:

• Use SHARED ownership for multi-writer scenarios
• Or assign different ownership_strength values for failover

---

LivelinessTimeout

Problem: A writer's liveliness lease has expired, indicating potential crash or network partition.

Symptoms:

• Large gaps in message timestamps
• Subscriber's on_liveliness_changed() callback triggered

Detection: Analyzes inter-message gaps vs. median arrival rate.

Fix:

// Configure appropriate lease duration
DataWriterQos qos;
qos.liveliness().kind = AUTOMATIC_LIVELINESS_QOS;
qos.liveliness().lease_duration = Duration_t(1, 0); // 1 second

---

ResourceLimitsNearMax

Problem: Resource usage approaching configured limits (max_samples, max_instances, history depth).

Symptoms:

• Sample rejection
• on_sample_rejected() callback triggered
• Memory pressure

Detection: Tracks message counts per topic vs. estimated limits.

Fix:

// Increase limits or add subscribers to consume faster
DataReaderQos qos;
qos.resource_limits().max_samples = 10000;
qos.history().depth = 100;

---

TypeConsistencyWarning

Problem: Different payload sizes detected on same topic, suggesting type mismatch.

Symptoms:

• Deserialization failures
• Corrupted data
• CDR decode errors

Detection: Clusters payload sizes and detects multimodal distributions.

Fix:

• Verify all publishers use identical IDL types
• Enable strict type checking:

TypeConsistencyEnforcementQosPolicy qos;
qos.kind = DISALLOW_TYPE_COERCION;

Severity Levels

Level	Color	Action Required
Critical	Red	Immediate attention - system may fail
High	Orange	Fix before production deployment
Medium	Yellow	Should be addressed
Low	Blue	Informational / optimization opportunity

CLI Usage

Run QoS analysis in headless mode:

# Text output
hdds-viewer --analyze capture.hddscap

# JSON output for CI/CD integration
hdds-viewer --analyze capture.hddscap --format json

# Exit code reflects highest severity
echo $?  # 0=OK, 1=Low, 2=Medium, 3=High, 4=Critical

Integration with CI/CD

# GitHub Actions example
- name: QoS Analysis
  run: |
    hdds-viewer --analyze test-capture.hddscap --format json > qos-report.json
    if [ $? -ge 3 ]; then
      echo "QoS issues detected!"
      exit 1
    fi

See Also

• QoS Policies Overview
• QoS Cheatsheet
• Troubleshooting Common Issues