Data collected by the Fast DDS Statistics module is published in one of the topics listed below. In order to simplify its use, the API provides aliases for the different statistics topics (see :ref:`api_statistics_topic_names`). The following table shows the correlation between the topic name and the corresponding alias.
| Topic name | Alias |
|---|---|
_fastdds_statistics_history2history_latency |
|HISTORY_LATENCY_TOPIC| |
_fastdds_statistics_network_latency |
|NETWORK_LATENCY_TOPIC| |
_fastdds_statistics_publication_throughput |
|PUBLICATION_THROUGHPUT_TOPIC| |
_fastdds_statistics_subscription_throughput |
|SUBSCRIPTION_THROUGHPUT_TOPIC| |
_fastdds_statistics_rtps_sent |
|RTPS_SENT_TOPIC| |
_fastdds_statistics_rtps_lost |
|RTPS_LOST_TOPIC| |
_fastdds_statistics_heartbeat_count |
|HEARTBEAT_COUNT_TOPIC| |
_fastdds_statistics_acknack_count |
|ACKNACK_COUNT_TOPIC| |
_fastdds_statistics_nackfrag_count |
|NACKFRAG_COUNT_TOPIC| |
_fastdds_statistics_gap_count |
|GAP_COUNT_TOPIC| |
_fastdds_statistics_data_count |
|DATA_COUNT_TOPIC| |
_fastdds_statistics_resent_datas |
|RESENT_DATAS_TOPIC| |
_fastdds_statistics_sample_datas |
|SAMPLE_DATAS_TOPIC| |
_fastdds_statistics_pdp_packets |
|PDP_PACKETS_TOPIC| |
_fastdds_statistics_edp_packets |
|EDP_PACKETS_TOPIC| |
_fastdds_statistics_discovered_entity |
|DISCOVERY_TOPIC| |
_fastdds_statistics_physical_data |
|PHYSICAL_DATA_TOPIC| |
The _fastdds_statistics_history2history_latency statistics topic collects data related with the latency between any
two matched endpoints.
This measurement provides information about the DDS overall latency independent of the user's application overhead.
Specifically, the measured latency corresponds to the time spent between the instant when the sample is written to the
DataWriter's history and the time when the sample is added to the DataReader's history and the notification is issued to
the corresponding user's callback.
The _fastdds_statistics_network_latency statistics topic collects data related with the network latency (expressed
in ns) between any two communicating locators.
This measurement provides information about the transport layer latency.
The measured latency corresponds to the time spent between the message being written in the |RTPSMessageGroup| until the
message being received in the |MessageReceiver|.
Important
In the case of :ref:`transport_tcp_tcp`, the reported latency also includes the time spent on the datagram's CRC related operations. Mind that is possible to disable CRC operations when defining the :ref:`transport_tcp_transportDescriptor`.
The _fastdds_statistics_publication_throughput statistics topic collects the amount of data (expressed in B/s)
that is being sent by each DataWriter.
This measurement provides information about the publication's throughput.
The _fastdds_statistics_subscription_throughput statistics topic collects the amount of data (expressed in B/s)
that is being received by each DataReader.
This measurement provides information about the subscription's throughput.
The _fastdds_statistics_rtps_sent statistics topic collects the number of RTPS packets and bytes that are being sent
from each DDS entity to each locator.
The _fastdds_statistics_rtps_lost statistics topic collects the number of RTPS packets and bytes that are being lost
in the transport layer (dropped somewhere in between) in the communication between each DDS entity and locator.
The _fastdds_statistics_heartbeat_count statistics topic collects the number of heartbeat messages sent by each
user's DataWriter.
This topic does not apply to builtin (related to :ref:`discovery`) and statistics DataWriters.
Heartbeat messages are only sent if the |ReliabilityQosPolicy| is set to |RELIABLE_RELIABILITY_QOS-api|.
These messages report the DataWriter's status.
The _fastdds_statistics_acknack_count statistics topic collects the number of acknack messages sent by each user's
DataReader.
This topic does not apply to builtin DataReaders (related to :ref:`discovery`).
Acknack messages are only sent if the |ReliabilityQosPolicy| is set to |RELIABLE_RELIABILITY_QOS-api|.
These messages report the DataReader's status.
The _fastdds_statistics_nackfrag_count statistics topic collects the number of nackfrag messages sent by each user's
DataReader.
This topic does not apply to builtin DataReaders (related to :ref:`discovery`).
Nackfrag messages are only sent if the |ReliabilityQosPolicy| is set to |RELIABLE_RELIABILITY_QOS-api|.
These messages report the data fragments that have not been received yet by the DataReader.
The _fastdds_statistics_gap_count statistics topic collects the number of gap messages sent by each user's
DataWriter.
This topic does not apply to builtin (related to :ref:`discovery`) and statistics DataWriters.
Gap messages are only sent if the |ReliabilityQosPolicy| is set to |RELIABLE_RELIABILITY_QOS-api|.
These messages report that some specific samples are not relevant to a specific DataReader.
The _fastdds_statistics_data_count statistics topic collects the total number of user's data messages and data
fragments (in case that the message size is large enough to require RTPS fragmentation) that have been sent by each
user's DataWriter.
This topic does not apply to builtin (related to :ref:`discovery`) and statistics DataWriters.
The _fastdds_statistics_resent_data statistics topic collects the total number of user's data messages and data
fragments (in case that the message size is large enough to require RTPS fragmentation) that have been necessary to
resend by each user's DataWriter.
This topic does not apply to builtin (related to :ref:`discovery`) and statistics DataWriters.
The _fastdds_statistics_sample_datas statistics topic collects the number of user's data messages (or data fragments
in case that the message size is large enough to require RTPS fragmentation) that have been sent by the user's
DataWriter to completely deliver a single sample.
This topic does not apply to builtin (related to :ref:`discovery`) and statistics DataWriters.
The _fastdds_statistics_pdp_packets statistics topic collects the number of PDP discovery traffic RTPS packets
transmitted by each DDS |DomainParticipant-api|.
PDP packets are the data messages exchanged during the PDP discovery phase (see :ref:`disc_phases` for more
information).
The _fastdds_statistics_edp_packets statistics topic collects the number of EDP discovery traffic RTPS packets
transmitted by each DDS |DomainParticipant-api|.
EDP packets are the data messages exchanged during the EDP discovery phase (see :ref:`disc_phases` for more
information).
The _fastdds_statistics_discovered_entity statistics topic reports the time when each local |DomainParticipant-api|
discovers any remote DDS entity (with the exception of those DDS entities related with the Fast DDS Statistics
module).
This topic also carries the |PHYSICAL_DATA_TOPIC| information for the case of discovered |DomainParticipant-api|; if the
discovered entity is either a |DataReader-api| or |DataWriter-api|, then the physical information is empty (see
:ref:`property_policies_physical_data` for more information about how to configure the physical data conveyed on the
discovery messages).
The _fastdds_statistics_physical_data statistics topic reports the host, user and process where the
Fast DDS Statistics module is running.