RTI Connext Core Libraries

The following issues affect backward compatibility in the Core Libraries starting in 7.x releases. Issues in the Core Libraries may affect components that use these libraries, including Infrastructure Services and Tools. Durable writer history, durable reader state, and Persistence Service no longer support external databases

As described in What’s New in 7.0.0, support for external databases was deprecated starting in release 6.1.1, and release 6.1.2 removed the ability to share a database connection (see Section In release 7, support for external databases (e.g., MySQL) is removed from the following features and components:

  • Durable writer history

  • Durable reader state

  • Persistence Service

In Persistence Service, use the <filesystem> tag instead of the <external_database> tag to store samples on disk.

Support for durable writer history and durable reader state has been temporarily disabled in Connext 7 releases because these features were only supported with external relational databases. RTI will provide a file-based storage option for durable writer history and durable reader state in a future release. Contact RTI Support at support@rti.com for additional information regarding durable writer history and durable reader state. Configuration Changes Communication with earlier releases when using DomainParticipant partitions

Connext 6.1.2 and earlier applications are part of the empty DomainParticipant partition. If you are using the new DomainParticipant partition feature in release 7 (see PARTITION QosPolicy, in the RTI Connext Core Libraries User’s Manual) and you want to communicate with earlier applications, change the configuration of the Connext 7 DomainParticipants to join the empty partition. For example:

      <element></element> <!-- empty partition -->
</partition> DDS_TransportMulticastQosPolicy will now fail if using TCP or TLS as transports

In previous releases, if the TRANSPORT_MULTICAST QoS Policy was configured with TCP or TLS as the transport, which is incompatible with multicast, the application ran without issue, simply not using multicast to send the data.

Now, if TCP or TLS is used as the multicast transport, the application will fail with an exception: “Multicast over TCP or TLS is not supported”. For example, the following QoS configuration will result in error:

</datareader_qos> Error for max_app_ack_response_length longer than 32kB

This issue affects you if you are setting max_app_ack_response_length to a value greater than 32kB.

Connext incorrectly allowed setting max_app_ack_response_length in the DATA_READER_RESOURCE_LIMITS QoS Policy longer than the maximum serializable data, resulting in the truncation of data when the length got close to 64kB.

Connext now enforces a maximum length of 32kB for max_app_ack_response_length as part of DataReader QoS consistency checks. Connext will now log an error if you try to set max_app_ack_response_length longer than 32kB. Potential unexpected delay in receiving samples due to randomization of sample sent time between min and max response delays

This issue affects you if the min_heartbeat_response_delay, max_heartbeat_response_delay, min_nack_response_delay, and max_nack_response_delay fields are not set to 0 in your application. By default they are not set to 0. (If you’re using any of the KeepLastReliable or StrictReliable builtin QoS profiles, such as “BuiltinQosLib::Generic.StrictReliable”, this issue will not affect you, because in those profiles the delays are set to 0.)

In releases after 6.1.2, the heartbeat and NACK response delays were not randomly generated between the minimum and maximum values. (These values are set in the min_heartbeat_response_delay, max_heartbeat_response_delay, min_nack_response_delay, and max_nack_response_delay fields.) The actual responses were closer to the minimum value (e.g., min_heartbeat_response_delay) than the maximum value (e.g., max_heartbeat_response_delay).

New in release 7, these delays are now truly random between the minimum and maximum values. This change may lead to an additional delay (up to the ‘max’ delay) in receiving samples in lossy environments or in starting to receive historical samples with transient local configuration. You may not have seen this delay before (assuming you are using the same configuration as before). You can reduce the delay by adjusting the ‘min’ and ‘max’ ranges for heartbeat and NACK responses. DataWriters no longer match DataReaders that request inline QoS

This change only affects you if you were setting reader_qos.protocol.expects_inline_qos to TRUE in your DataReaders, which should not be the case. (This issue may affect you if you interact with other vendors’ DataReaders that set expects_inline_qos to TRUE; however, in that case, communication likely did not occur, because Connext DataWriters do not send inline QoSes.)

Previously, Connext DataWriters matched DataReaders that set expects_inline_qos in the DATA_READER_PROTOCOL QoS Policy to TRUE. This behavior was incorrect because Connext DataWriters do not support sending inline QoS; they were not honoring the DataReaders’ requests and therefore they should not have matched.

In release 7, DataWriters no longer match DataReaders that request inline QoS (i.e., DataReaders that set reader_qos.protocol.expects_inline_qos to TRUE). Reduced number of participant announcements at startup

In previous releases, when a DomainParticipant was first created it sent out a participant announcement and then DiscoveryConfigQos.initial_participant_announcements number of announcements in addition to the first one. Starting in release 7, initial_participant_announcements configures the exact number of announcements that are sent out when a participant is created, there is no additional announcement. API Compatibility C# project upgrade

See Upgrading Your C# Projects. C API PolicyHelper read-only functions receive a const input

In the C API, the following functions have changed their policy parameters from non-const to const:

  • DDS_PropertyQosPolicyHelper_lookup_property

  • DDS_PropertyQosPolicyHelper_lookup_property_with_prefix

  • DDS_PropertyQosPolicyHelper_get_properties

  • DDS_DataTagQosPolicyHelper_lookup_tag

As a result, if you were previously casting the policy parameter to a non-const in order to avoid a -Wdiscarded-qualifiers gcc warning, you should now remove this cast. Memory leak when using coherent sets and the Copy Take/Read APIs in C

This issue affects you if you are using coherent sets and the copy take/read APIs (such as take_next_sample) in C, C++, modern C++, and Java.

Before release 7, the field SampleInfo::coherent_set_info was not copied when using the copy take/read APIs (such as take_next_sample) in C, C++, modern C++, and Java. This behavior has changed in release 7, and the optional field SampleInfo::coherent_set_info is now copied. Consequently, you will need to call the DDS_SampleInfo_finalize API in C to finalize the SampleInfo objects to avoid memory leaks. There should not be side effects in other languages, because the memory will be released when the object is destroyed. Changes to DataReader read/take methods in Python API

In previous releases, the read/take operations of IDL-based readers (dds.DataReader) and DynamicData readers (dds.DynamicData.DataReader) were not equivalent. Release 7.1.0 makes the reader APIs equivalent. See API Improvements, in What’s New in 7.1.0 for a list of the changes made to dds.DynamicData.DataReader, builtin discovery readers (such as dds.ParticipantBuiltinTopicData.DataReader), dds.DataReader, and each DataReader’s Selector class. Library Size

In release 7, the size of the libraries increased as expected compared to 6.1.1/6.1.2, due to the addition of new functionality. The following table shows the differences:

Table 2.1 Library Size Comparison for x64Linux3gcc4.8.2 in Bytes



Change (%)













libnddscore.so (Core Library)




libnddssecurity.so (Security Plugins Library)



+4.56 Memory Consumption

In general, release 7 applications will consume more heap memory than 6.1.1/6.1.2 applications. Stack size is similar between the two releases; there are no significant changes in the stack size.

The following table shows the heap memory differences:

Table 2.2 Memory Comsumption Comparison for x64Linux3gcc4.8.2 in Bytes



Change (%)









































Remote DataReader




Remote DataWriter




Instance registered in DataReader




Sample stored in DataReader




Remote Participant



+3.82 Network Performance

In general, release 7 applications have the same performance as in 6.1.1/6.1.2 for user data exchange. For details, see RTI Connext Performance Benchmarks. Discovery Performance Simple Participant Discovery: reduced bandwidth usage may delay discovery time

In earlier Connext releases, when a participant discovered a new participant, it sent its participant announcement back to the new participant as well as to all other discovered peers and its initial peers list an initial_participant_announcements number of times. In release 7, the participant announcement is sent only to the new participant a new_remote_participant_announcements number of times. The other discovered participants already have this information, so, previously, a lot of the traffic when a new participant was discovered was wasted bandwidth. The default new_remote_participant_announcements value is also smaller than initial_participant_announcements to reduce bandwidth usage. These are improvements to reduce unnecessary bandwidth usage, but they have the side effect of potentially delaying discovery between two participants that miss each other’s participant announcements.

For example, consider three participants: A, B, and C. Participant A has Participant B in its initial peers list, and B has A in its list as well. They were both started at the same time, along with 100 other participants, so all of their participant announcements to each other were dropped by the network due to buffer overflows. So A and B do not discover each other. Now, Participant C joins with participant A in its initial peers list. In earlier Connext versions, A would respond to C, as well as send an announcement to B, therefore triggering discovery between A and B (if A and B have already discovered each other, this message would be redundant and wasted bandwidth). In release 7, however, A will only respond directly to C. Participants A and B will discover each other at the next participant_liveliness_assert_period (or the participant_announcement_period if you are using Simple Participant Discovery 2.0) when they send out their periodic participant announcement to their peers.

There are a number of QoSs that can be used to speed up discovery in these cases. You can increase the number of initial_participant_announcements and/or the new_remote_participant_announcements that are sent, elongating the potential discovery phase and hedging against dropped packets. You can also try increasing the separation between the min_initial_announcement_period and max_initial_announcement_period. The initial_participant_announcements and new_remote_participant_announcements are sent at a random time between the min/max initial_anouncement_period values, making the likelihood of collisions and dropped packets less likely. The final thing to try is to increase the receive buffer sizes of the Connext transports that you are using, as well as of the OS/kernel layers, to prevent against dropped packets.

For details on discovery performance, see RTI Connext Performance Benchmarks. (Experimental) Simple Participant Discovery 2.0: interaction with Security Plugins

There are currently known scalability challenges with large-scale systems using the Security Plugins in combination with Simple Participant Discovery 2.0, where “large” means multiple hundreds of participants discovering each other at once. These issues may manifest as excess bandwidth usage, lack of complete discovery, liveliness lost events, or incomplete authentication periods. These issues will be addressed in upcoming releases.