8.3. Real-Time Data¶
A Dynamic or Real-Time series displays the data that is being received by the monitor in the current moment. This is a pseudo-real-time display of a running DDS network. Pseudo because it is not an exact representation of the DDS network activity in the exact moment it is represented, as it represents instead a periodical update of the last seconds of the network.
Every data displayed is delayed by 5 seconds in order to accurately represent all the data reported by the network. This is because the data is not instantly reported by Fast DDS, and thus the data used to update the chart might be complete.
8.3.1. Create Dynamic Series Chartbox¶
In order to create a new dynamic Chartbox in the central panel, use the button Display Real-Time Data in the Edit or in Shortcuts Bar. A dynamic Chartbox can only contain series referring the same DataKind. A new dialog will appear asking to choose some parameters that will be shared among all the series created in this new Chartbox.
8.3.1.1. Data Kind¶
Check the common parameters explanation in Data kind.
8.3.1.2. Time window¶
This parameter is the default size and value of the X axis. The X axis will be set by default to have the current moment as the rightmost point when initialized. The X axis leftmost point will be the current time minus the size of the Time window.
8.3.1.3. Update period¶
This parameter refers to the time elapsed between two updates of the Chartbox series. Each of the series inside the Chartbox will be updated with the new data collected every Update period seconds.
8.3.1.4. Advanced: Maximum data points¶
This parameter sets the default for the maximum amount of data points that all series in this Chartbox will have. Check the Advanced: Maximum data points section for more information.
Clicking OK will create a new Chartbox referring the DataKind chosen that the dynamic series will hold.
8.3.2. Create Dynamic Series Dialog¶
The Create Series Dialog allows users to create a new data series within a Chartbox. The fields in the dialog configure the data that will be displayed. When all the data has been set in the Create Dynamic Series Chartbox, press Add to create the series and continue with the same parameter set in order to create a new series. Press Add & Close to create the series and close the dialog. Press Close to close the window without creating any series.
8.3.2.1. Series label¶
Check the common parameters explanation in Series label.
8.3.2.2. Source Entity Id¶
Check the common parameters explanation in Source Entity Id.
8.3.2.3. Target Entity Id¶
Check the common parameters explanation in Target Entity Id.
8.3.2.4. Statistics kind¶
This parameter behaves as it is explained in Statistics kind except for RAW_DATA kind. Selecting RAW_DATA as Statistics kind will display every data available in the interval of time given by Update period with no accumulation.
Note
The data will not be displayed at the time it arrives in any case. It will always appear displayed after each Update period.
8.3.2.5. Advanced: Maximum data points¶
This parameter sets a limit on the number of data points displayed for a specific data series.
Data points are dynamically added to the series, which may generate an efficiency problem due to memory exhaustion.
To prevent this issue, the parameter restricts the number of data points by removing older data as new points are
being added. Use value 0 for unlimited series.
This value can be changed per series at any time in the series menu.
8.3.2.6. Advanced: Cumulative data¶
This option allows the user to define the time interval for which the statistic selected in “Statistic kind” is to be calculated. That is, in case the user selects a time interval to obtain accumulated statistics data, the statistics will be applied to all the data collected by the monitor in that defined time interval. This allows the update interval of the chart and the time interval for calculating the statistics to be independent.
Let’s look into a simple example of monitoring the latency of a publisher and a subscriber in the Shapes Demo application launched with statistics enabled (a detailed example of Fast DDS Monitor monitoring a Shapes Demo application is shown in the following video tutorial). First, a chart is created to monitor the application latency with a time window of 5 minutes and an update period of 5 seconds. Then the dialog box for creating series in the graph is opened. Select your host as source and target entities and the DataWriters and DataReaders running on your machine will be automatically detected. Select the mean as the type of statistical measurement to be applied. Finally, create three series with three different types of accumulation:
No accumulation. The average latency between publisher and subscriber in the last update period, 5 seconds in this particular case, is calculated.
With accumulation from the first available data point. This calculates the average latency between publisher and subscriber from the time the monitor has the first available data until the current time. This current instant is updated every update period, adding new points to the calculated statistic.
With accumulation by setting a time interval. The average latency between publisher and subscriber is calculated from the current time minus the cumulative time interval set until the current time.
Below is an image of the three series created. It can be seen that the series with a longer accumulation period tends to have a steady latency value, being less susceptible to strong but momentary latency variations. On the contrary, the series that calculates the average latency with the available data of the last 5 seconds shows a large variation due to the smaller number of data points available for the calculation of the statistic.
8.3.2.7. Quick explanation of the data displayed¶
First, the application will create an empty chart where X axis represents the time between the current moment and that time minus the Time window size. This window is permanently moving in order to always represent the current time. This X axis movement can be paused in order to move and resize the chart at any moment, and new data will still appear.
Every Update period, new data will be displayed on the right side of the chart. The new data displayed references the cumulative value of the data that has been stored in that amount of time.
Warning
Some of the data queried could not exist in the database for many reasons, i.e. the entity did not report anything in the time where the query requires data. In these cases, after an Update period there will not appear any point and the chart will be connected with the next interval with data.