2.1.3. Memory Performance¶

This document describes memory usage for RTI Connext Professional 6.1. The goal is to provide an idea of how much memory is used by the libraries and the DDS entities. This document does not provide exact formulas and numbers for every possible configuration of the software.

2.1.3.1. Platforms and Libraries¶

Our measurements have been gathered for the following platform using a custom C++ benchmark application:

Linux: x64 Ubuntu 20.04 using RTI Connext 6.1.2 release target libraries for x64Linux4gcc7.3.0.

2.1.3.2. Program Memory¶

These numbers reflect the memory required to load the dynamic libraries when executing code that includes RTI Connext.

For Linux and macOS, we measured the text size by calling the size command for each library. For Windows, we measured this size as the mapped size shown by the Process Explorer.

Library/Architecture	x64 Linux (x64Linux4gcc7.3.0)
libnddscpp (Traditional C++ Binding Library)	1653271 Bytes
libnddscpp2 (Modern C++ Binding Library)	1276420 Bytes
libnddsc (C Binding Library)	6620230 Bytes
libnddscore (Core Funtionalities Library)	7163684 Bytes
libnddssecurity (Security Plugins Library)	730895 Bytes

Note

The libraries tested are the release versions. These can be found in the <$NDDSHOME>/lib/<$ARCHITECTURE> folder.

2.1.3.3. RTI Threads¶

This section provides the default and minimum stack size for all the different threads created by the middleware. This includes the following threads:

Database thread
Event thread
Receive threads
Asynchronous publishing thread
Batching thread

The actual number of threads created by the middleware will depend on the configuration of several QoS policies, such as the ASYNCHRONOUS_PUBLISHER or BATCH QoS Policies.

By default, the stack size value assigned to each thread depends on the platform and OS. This value can be modified by updating the thread stack size QoS value, but a minimum value is required.

Thread	Default Stack Size	Minimum Stack Size
User thread	OS default	40.4 kB
Database thread	OS default	7.8 kB
Event thread	OS default	18.0 kB
Receiver thread	OS default	25.0 kB
Asynchronous publishing thread	OS default	7.8 kB
Batch thread	OS default	7.8 kB

Note

The Minimum Stack Size value refers to the minimum stack size needed for a given thread. This value assumes no user-specific stack space is needed; therefore, if the user adds any data on the thread’s stack, that size must be taken into account.

Note

On Linux, the OS default can be obtained by invoking the ulimit command. In the Ubuntu machines we used, this size was 10240 kB.

(+) Click to know more about the different thread types in Connext

DataBase Thread (also referred to as the Database cleanup thread) is created to garbage-collect records related to deleted entities from the in-memory database used by the middleware. There is one database thread per DomainParticipant.
Event Thread handles all timed events, including checking for timeouts and deadlines as well as sending periodic heartbeats and repair traffic. There is one event thread per DomainParticipant.
Receive Threads are used to receive and process the data from the installed transports. There is one receive thread per (transport, receive port) pair. When using the builtin UDPv4 and SHMEM transports (with the default configuration), Connext creates five receive threads:
For discovery:
- Two for unicast (one for UDPv4, one for SHMEM)
- One for multicast (for UDPv4)
For user data:
- Two for unicast (one for UDPv4, one for SHMEM)
Asynchronous Publishing Thread handles the data transmission when asynchronous publishing is enabled in a DataWriter. There is one asynchronous publishing thread per Publisher. This thread is created only if there is one DataWriter enabling asynchronous publishing in the Publisher.
Batch Thread handles the asynchronous flushing of a batch when batching is enabled in a DataWriter and the flush_period is set to a value different than DDS_DURATION_INFINITE. There is one batch thread per Publisher. This thread is created only if there is one DataWriter enabling batching and setting a finite flush_period in the Publisher.

2.1.3.4. RTI Transports¶

This section provides the memory allocated by the OS for the builtin transports UDPv4, UDPv6, and SHMEM, using the default QoS settings.

When using UDPv4 with the default configuration, Connext uses the following for each new DomainParticipant created:

One receive socket to receive Unicast-Discovery data
One receive socket to receive Multicast-Discovery data
One receive socket to receive Unicast-UserData data
One socket to send Unicast data
N sockets to send Multicast-Discovery data where N is the number of multicast interfaces in the host

The port assigned for the receive socket depends on the domain ID and participant ID. The same number of sockets are opened when using UDPv6.

Size of the buffers

The receive and send socket buffer size can be configured by modifying the transport QoS settings. By default, these values are as follows:

Buffer Size	UDPv4	UDPv6
Receive socket	131072 bytes	131072 bytes
Send socket	131072 bytes	131072 bytes

For SHMEM, Connext will use by default:

One shared memory buffer for Unicast-Discovery data
One shared memory buffer for Unicast-UserData data

Size of the buffers

The receive and send socket buffer size can be configured by modifying the transport QoS settings. By default. For SHMEM, the value depends on the maximum size of the SHMEM message and the maximum number of SHMEM received messages:

(SHMEM_RECEIVED_MESSAGE_COUNT_MAX_DEFAULT * SHMEM_MESSAGE_SIZE_MAX_DEFAULT / 4) = ( 64 * 65536 / 4) = 1048576

Buffer Size	SHMEM
Receive socket	1048576 bytes

2.1.3.5. Heap Usage of Connext Entities¶

RTI has designed and implemented a benchmark application that measures the memory that is directly allocated by the middleware using malloc(). Additionally, the Connext libraries also request the OS to allocate other memory, including:

Socket buffers (see RTI Transports)
Shared memory regions (see RTI Transports)
Thread stacks (see see RTI Threads)

All the memory allocated by the OS can be tuned using QoS parameters or DDS transport properties.

The following tables report the average heap allocation for the different DDS entities that can be used in a Connext application.

The amount of memory required for an entity depends on the value of different QoS policies. For this benchmark, RTI has used a QoS profile that minimizes the memory usage. The profile is provided in a separate XML file and is described in Minimum QoS Settings.

Entity	Size (Bytes)
Participant Factory	64070
Participant	1963353
Type	1450
Topic	2168
Subscriber	9586
Publisher	3663
DataReader	73432
DataWriter	43699
Instance	488
Sample	1347
Remote Readers	7503
Remote Writers	15459
Reader Instance	887
Reader Samples	917
Remote Participant	82189

The memory reported for samples and instances does not include the user data, only the meta-data.

Note

To efficiently manage the creation and deletion of DDS entities and samples, Connext implements its own memory manager. The memory manager allocates and manages multiple buffers to avoid continuous memory allocation. Therefore, the memory growth does not necessarily follow linearly with the creation of DDS entities and samples. The pre-allocation scheme of the memory manager is configurable.

2.1.3.6. Minimum QoS Settings¶

To obtain the results mentioned above, we used the MinimalMemoryFootPrint profile, included in the builtin profiles. This profile minimizes the use of memory, and can be seen below:

<domain_participant_qos>

    <transport_builtin>
      <mask>UDPv4</mask>
    </transport_builtin>

    <discovery_config>
      <publication_reader_resource_limits>
        <initial_samples>1</initial_samples>
        <max_samples>LENGTH_UNLIMITED</max_samples>
        <max_samples_per_read>1</max_samples_per_read>
        <dynamically_allocate_fragmented_samples>true</dynamically_allocate_fragmented_samples>
        <initial_infos>1</initial_infos>
        <initial_outstanding_reads>1</initial_outstanding_reads>
        <initial_fragmented_samples>1</initial_fragmented_samples>
      </publication_reader_resource_limits>
      <subscription_reader_resource_limits>
        <initial_samples>1</initial_samples>
        <max_samples>LENGTH_UNLIMITED</max_samples>
        <max_samples_per_read>1</max_samples_per_read>
        <dynamically_allocate_fragmented_samples>true</dynamically_allocate_fragmented_samples>
        <initial_infos>1</initial_infos>
        <initial_outstanding_reads>1</initial_outstanding_reads>
        <initial_fragmented_samples>1</initial_fragmented_samples>
      </subscription_reader_resource_limits>
      <participant_reader_resource_limits>
        <initial_samples>1</initial_samples>
        <max_samples>LENGTH_UNLIMITED</max_samples>
        <max_samples_per_read>1</max_samples_per_read>
        <dynamically_allocate_fragmented_samples>true</dynamically_allocate_fragmented_samples>
        <initial_infos>1</initial_infos>
        <initial_outstanding_reads>1</initial_outstanding_reads>
        <initial_fragmented_samples>1</initial_fragmented_samples>
      </participant_reader_resource_limits>
    </discovery_config>

    <resource_limits>
      <transport_info_list_max_length>0</transport_info_list_max_length>
      <local_writer_allocation>
        <incremental_count>1</incremental_count>
        <initial_count>1</initial_count>
        <max_count>LENGTH_UNLIMITED</max_count>
      </local_writer_allocation>
      <local_reader_allocation>
        <incremental_count>1</incremental_count>
        <initial_count>1</initial_count>
        <max_count>LENGTH_UNLIMITED</max_count>
      </local_reader_allocation>
      <local_publisher_allocation>
        <incremental_count>1</incremental_count>
        <initial_count>1</initial_count>
        <max_count>LENGTH_UNLIMITED</max_count>
      </local_publisher_allocation>
      <local_subscriber_allocation>
        <incremental_count>1</incremental_count>
        <initial_count>1</initial_count>
        <max_count>LENGTH_UNLIMITED</max_count>
      </local_subscriber_allocation>
      <local_topic_allocation>
        <incremental_count>1</incremental_count>
        <initial_count>1</initial_count>
        <max_count>LENGTH_UNLIMITED</max_count>
      </local_topic_allocation>
      <remote_writer_allocation>
        <incremental_count>1</incremental_count>
        <initial_count>1</initial_count>
        <max_count>LENGTH_UNLIMITED</max_count>
      </remote_writer_allocation>
      <remote_reader_allocation>
        <incremental_count>1</incremental_count>
        <initial_count>1</initial_count>
        <max_count>LENGTH_UNLIMITED</max_count>
      </remote_reader_allocation>
      <remote_participant_allocation>
        <incremental_count>1</incremental_count>
        <initial_count>1</initial_count>
        <max_count>LENGTH_UNLIMITED</max_count>
      </remote_participant_allocation>
      <matching_writer_reader_pair_allocation>
        <incremental_count>1</incremental_count>
        <initial_count>1</initial_count>
        <max_count>LENGTH_UNLIMITED</max_count>
      </matching_writer_reader_pair_allocation>
      <matching_reader_writer_pair_allocation>
        <incremental_count>1</incremental_count>
        <initial_count>1</initial_count>
        <max_count>LENGTH_UNLIMITED</max_count>
      </matching_reader_writer_pair_allocation>
      <ignored_entity_allocation>
        <incremental_count>1</incremental_count>
        <initial_count>1</initial_count>
        <max_count>LENGTH_UNLIMITED</max_count>
      </ignored_entity_allocation>
      <content_filter_allocation>
        <incremental_count>1</incremental_count>
        <initial_count>1</initial_count>
        <max_count>LENGTH_UNLIMITED</max_count>
      </content_filter_allocation>
      <content_filtered_topic_allocation>
        <incremental_count>1</incremental_count>
        <initial_count>1</initial_count>
        <max_count>LENGTH_UNLIMITED</max_count>
      </content_filtered_topic_allocation>
      <read_condition_allocation>
        <incremental_count>1</incremental_count>
        <initial_count>1</initial_count>
        <max_count>LENGTH_UNLIMITED</max_count>
      </read_condition_allocation>
      <query_condition_allocation>
        <incremental_count>1</incremental_count>
        <initial_count>1</initial_count>
        <max_count>LENGTH_UNLIMITED</max_count>
      </query_condition_allocation>
      <outstanding_asynchronous_sample_allocation>
        <incremental_count>1</incremental_count>
        <initial_count>1</initial_count>
        <max_count>LENGTH_UNLIMITED</max_count>
      </outstanding_asynchronous_sample_allocation>
      <flow_controller_allocation>
        <incremental_count>1</incremental_count>
        <initial_count>4</initial_count>
        <max_count>LENGTH_UNLIMITED</max_count>
      </flow_controller_allocation>

      <local_writer_hash_buckets>1</local_writer_hash_buckets>
      <local_reader_hash_buckets>1</local_reader_hash_buckets>
      <local_publisher_hash_buckets>1</local_publisher_hash_buckets>
      <local_subscriber_hash_buckets>1</local_subscriber_hash_buckets>
      <local_topic_hash_buckets>1</local_topic_hash_buckets>
      <remote_writer_hash_buckets>1</remote_writer_hash_buckets>
      <remote_reader_hash_buckets>1</remote_reader_hash_buckets>
      <remote_participant_hash_buckets>1</remote_participant_hash_buckets>
      <matching_reader_writer_pair_hash_buckets>1</matching_reader_writer_pair_hash_buckets>
      <matching_writer_reader_pair_hash_buckets>1</matching_writer_reader_pair_hash_buckets>
      <ignored_entity_hash_buckets>1</ignored_entity_hash_buckets>
      <content_filter_hash_buckets>1</content_filter_hash_buckets>
      <content_filtered_topic_hash_buckets>1</content_filtered_topic_hash_buckets>
      <flow_controller_hash_buckets>1</flow_controller_hash_buckets>

      <max_gather_destinations>16</max_gather_destinations>

      <participant_user_data_max_length>8</participant_user_data_max_length>
      <topic_data_max_length>0</topic_data_max_length>
      <publisher_group_data_max_length>0</publisher_group_data_max_length>
      <subscriber_group_data_max_length>0</subscriber_group_data_max_length>

      <writer_user_data_max_length>16</writer_user_data_max_length>
      <reader_user_data_max_length>16</reader_user_data_max_length>

      <max_partitions>0</max_partitions>
      <max_partition_cumulative_characters>0</max_partition_cumulative_characters>

      <type_code_max_serialized_length>0</type_code_max_serialized_length>
      <type_object_max_deserialized_length>0</type_object_max_deserialized_length>
      <type_object_max_serialized_length>0</type_object_max_serialized_length>
      <deserialized_type_object_dynamic_allocation_threshold>0</deserialized_type_object_dynamic_allocation_threshold>
      <serialized_type_object_dynamic_allocation_threshold>0</serialized_type_object_dynamic_allocation_threshold>

      <contentfilter_property_max_length>1</contentfilter_property_max_length>
      <participant_property_list_max_length>0</participant_property_list_max_length>
      <participant_property_string_max_length>0</participant_property_string_max_length>
      <writer_property_list_max_length>0</writer_property_list_max_length>
      <writer_property_string_max_length>0</writer_property_string_max_length>
      <max_endpoint_groups>0</max_endpoint_groups>
      <max_endpoint_group_cumulative_characters>0</max_endpoint_group_cumulative_characters>

      <channel_seq_max_length>0</channel_seq_max_length>
      <channel_filter_expression_max_length>0</channel_filter_expression_max_length>
      <writer_data_tag_list_max_length>0</writer_data_tag_list_max_length>
      <writer_data_tag_string_max_length>0</writer_data_tag_string_max_length>
      <reader_data_tag_list_max_length>0</reader_data_tag_list_max_length>
      <reader_data_tag_string_max_length>0</reader_data_tag_string_max_length>
    </resource_limits>

    <database>
      <initial_weak_references>256</initial_weak_references>
      <max_weak_references>1000000</max_weak_references>
      <shutdown_cleanup_period>
        <sec>0</sec>
        <nanosec>100000000</nanosec>
      </shutdown_cleanup_period>
    </database>

    <property inherit="false">
      <value>
      </value>
    </property>

  </domain_participant_qos>

  <datawriter_qos>

    <reliability>
      <kind>RELIABLE_RELIABILITY_QOS</kind>
    </reliability>

    <history>
      <kind>KEEP_ALL_HISTORY_QOS</kind>
    </history>

    <resource_limits>
      <initial_instances>1</initial_instances>
      <initial_samples>1</initial_samples>
      <instance_hash_buckets>1</instance_hash_buckets>
    </resource_limits>

  </datawriter_qos>

  <datareader_qos>

    <reliability>
      <kind>RELIABLE_RELIABILITY_QOS</kind>
    </reliability>

    <history>
      <kind>KEEP_ALL_HISTORY_QOS</kind>
    </history>

    <resource_limits>
      <initial_instances>1</initial_instances>
      <initial_samples>1</initial_samples>
    </resource_limits>

    <reader_resource_limits>
      <max_samples_per_read>1</max_samples_per_read>
      <initial_infos>1</initial_infos>
      <initial_outstanding_reads>1</initial_outstanding_reads>
      <initial_remote_writers>1</initial_remote_writers>
      <initial_remote_writers_per_instance>1</initial_remote_writers_per_instance>
      <initial_fragmented_samples>1</initial_fragmented_samples>
      <dynamically_allocate_fragmented_samples>1</dynamically_allocate_fragmented_samples>
      <initial_remote_virtual_writers>1</initial_remote_virtual_writers>
      <initial_remote_virtual_writers_per_instance>1</initial_remote_virtual_writers_per_instance>
      <max_query_condition_filters>0</max_query_condition_filters>
    </reader_resource_limits>

  </datareader_qos>

  <topic_qos>
    <resource_limits>
      <initial_samples>1</initial_samples>
      <initial_instances>1</initial_instances>
      <instance_hash_buckets>1</instance_hash_buckets>
    </resource_limits>
  </topic_qos>
</qos_profile>