13.1. Non consolidated QoS

The PropertyPolicyQos Options are used to develop new eProsima Extensions QoS. Before consolidating a new QoS Policy, it is usually set using this generic QoS Policy. Consequently, this section is prone to frequent updates so the user is advised to check latest changes after upgrading to a different release version.

13.1.1. DataWriter operating mode QoS Policy

By default, Fast DDS DataWriters are enabled using push mode. This implies that they will add new samples into their queue, and then immediately deliver them to matched readers. For writers that produce non periodic bursts of data, this may imply saturating the network with a lot of packets, increasing the possibility of losing them on unreliable (i.e. UDP) transports. Depending on their QoS, DataReaders may also have to ignore some received samples, so they will have to be resent.

Configuring the DataWriters on pull mode offers an alternative by letting each reader pace its own data stream. It works by the writer notifying the reader what it is available, and waiting for it to request only as much as it can handle. At the cost of greater latency, this model can deliver reliability while using far fewer packets than push mode.

DataWriters periodically announce the state of their queue by means of a heartbeat. Upon reception of the heartbeat, DataReaders will request the DataWriter to send the samples they want to process. Consequently, the publishing rate can be tuned setting the heartbeat period accordingly. See Tuning Heartbeat Period for more details.

PropertyPolicyQos name

PropertyPolicyQos value

Default value

"fastdds.push_mode"

"true"/"false"

"true"

C++

DataWriterQos wqos;

// Enable pull mode
wqos.properties().properties().emplace_back(
    "fastdds.push_mode",
    "false");

XML

<?xml version="1.0" encoding="UTF-8" ?>
<profiles xmlns="http://www.eprosima.com/XMLSchemas/fastRTPS_Profiles">
<data_writer profile_name="pull_mode_datawriter_xml_profile">
    <propertiesPolicy>
        <properties>
            <!-- Enable pull mode -->
            <property>
                <name>fastdds.push_mode</name>
                <value>false</value>
            </property>
        </properties>
    </propertiesPolicy>
</data_writer>
</profiles>

Note

Warning

13.1.2. Unique network flows QoS Policy

Warning

This section is still under work.

13.1.3. Statistics Module Settings

Fast DDS Statistics Module uses the PropertyPolicyQos to indicate the statistics DataWriters that are enabled automatically (see Automatically enabling statistics DataWriters). In this case, the property value is a semicolon separated list containing the statistics topic name aliases of those DataWriters that the user wants to enable.

PropertyPolicyQos name

PropertyPolicyQos value

Default value

"fastdds.statistics"

Semicolon separated list of statistics topic name aliases

""

C++

DomainParticipantQos pqos;

// Activate Fast DDS Statistics module
pqos.properties().properties().emplace_back("fastdds.statistics",
        "HISTORY_LATENCY_TOPIC;ACKNACK_COUNT_TOPIC;DISCOVERY_TOPIC;PHYSICAL_DATA_TOPIC");

XML

<participant profile_name="statistics_domainparticipant_conf_xml_profile">
    <rtps>
        <propertiesPolicy>
            <properties>
                <!-- Activate Fast DDS Statistics Module -->
                <property>
                    <name>fastdds.statistics</name>
                    <value>HISTORY_LATENCY_TOPIC;ACKNACK_COUNT_TOPIC;DISCOVERY_TOPIC;PHYSICAL_DATA_TOPIC</value>
                </property>
            </properties>
        </propertiesPolicy>
    </rtps>
</participant>

13.1.4. Endpoint Partitions

Fast DDS uses this PropertyPolicyQos to define which partitions does an endpoint belong to. This property follows the same logic regarding matching as the PartitionQosPolicy that can be defined for Publishers and Subscribers.

This property’s value is a semicolon separated list containing the partition names the user wants this endpoint to belong to.

Important

If both a Publisher and one of its DataWriters have conflicting partition configuration, this is, a DataWriter has this property defined while the Publisher has the PartitionQosPolicy defined, the DataWriter configuration takes precedence and the Publisher PartitionQosPolicy is ignored for this endpoint. This applies to Subscribers and their DataReaders as well.

This property will be automatically set when creating DataReaders and DataWriters using the create_with_profile functions. It cannot be changed after the entity has been created.

PropertyPolicyQos name

PropertyPolicyQos value

Default value

"partitions"

Semicolon separated list of partition names

""

C++

DataWriterQos wqos;

// Add partitions
wqos.properties().properties().emplace_back(
    "partitions",
    "part1;part2");

DataReaderQos rqos;

// Add partitions
rqos.properties().properties().emplace_back(
    "partitions",
    "part1;part2");

XML

<data_writer profile_name="pub_partition_example">
    <qos>
        <partition>
            <names>
                <name>part1</name>
                <name>part2</name>
            </names>
        </partition>
    </qos>
</data_writer>

<data_reader profile_name="sub_partition_example">
    <qos>
        <partition>
            <names>
                <name>part1</name>
                <name>part2</name>
            </names>
        </partition>
    </qos>
</data_reader>