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QoS Policies Overview

DDS provides 22 Quality of Service policies to fine-tune data distribution behavior. HDDS implements all standard policies from DDS v1.4.

Most Important Policies​

PolicyDescriptionDefault
ReliabilityDelivery guaranteeBEST_EFFORT
DurabilityData persistenceVOLATILE
HistorySample bufferingKEEP_LAST(10)
DeadlineUpdate frequencyInfinite
LivelinessFailure detectionAUTOMATIC

All 22 QoS Policies​

Data Distribution​

PolicyPurpose
ReliabilityBEST_EFFORT vs RELIABLE delivery
HistoryKEEP_LAST(n) vs KEEP_ALL buffering
DurabilityVOLATILE, TRANSIENT_LOCAL, PERSISTENT
DurabilityServiceLate-joiner delivery configuration
ResourceLimitsMax samples, instances, memory

Timing​

PolicyPurpose
DeadlineMaximum time between samples
LatencyBudgetAcceptable delay hint
LifespanData expiration time
TimeBasedFilterMinimum separation between samples

Ownership​

PolicyPurpose
OwnershipSHARED vs EXCLUSIVE writer control
OwnershipStrengthPriority for exclusive ownership

Ordering​

PolicyPurpose
DestinationOrderBY_RECEPTION_TIMESTAMP vs BY_SOURCE_TIMESTAMP
PresentationCoherent/ordered access scope

Lifecycle​

PolicyPurpose
LivelinessAUTOMATIC, MANUAL_BY_PARTICIPANT, MANUAL_BY_TOPIC
WriterDataLifecycleAuto-dispose unregistered instances
ReaderDataLifecycleAuto-purge samples without writers
EntityFactoryAuto-enable child entities

Metadata​

PolicyPurpose
UserDataCustom user metadata
TopicDataTopic-level metadata
GroupDataPublisher/Subscriber metadata
PartitionLogical data separation
TransportPriorityNetwork QoS hint

Quick Start​

use hdds::prelude::*;

// Create QoS with builder pattern
let writer_qos = DataWriterQos::default()
    .reliability(Reliability::Reliable {
        max_blocking_time: Duration::from_secs(1),
    })
    .durability(Durability::TransientLocal)
    .history(History::KeepLast { depth: 10 });

let writer = publisher.create_writer_with_qos(&topic, writer_qos)?;

QoS Profiles​

HDDS provides built-in profiles for common scenarios:

// Low latency (gaming, real-time control)
let qos = QosProfile::low_latency();
// → KeepLast(1), 100KB quota

// High throughput (bulk data transfer)
let qos = QosProfile::high_throughput();
// → KeepLast(1000), 50MB quota

// Reliable (guaranteed delivery)
let qos = QosProfile::reliable();
// → Reliable, TransientLocal, KeepLast(100)

QoS Compatibility​

Writers and readers must have compatible QoS to communicate:

WriterReaderResult
RELIABLERELIABLEMatch
RELIABLEBEST_EFFORTMatch
BEST_EFFORTRELIABLENo Match
BEST_EFFORTBEST_EFFORTMatch
Compatibility

A BEST_EFFORT writer cannot satisfy a RELIABLE reader. The reader expects acknowledgments that the writer won't send.

Resource Limits​

Control memory usage with ResourceLimits:

let qos = DataWriterQos::default()
    .resource_limits(ResourceLimits {
        max_samples: 100_000,           // Total samples
        max_instances: 1,                // Number of instances
        max_samples_per_instance: 100_000, // Per-instance queue
        max_quota_bytes: 100 * 1024 * 1024, // 100 MB
    });

Next Steps​