Memory optimization

This section explains how memory is managed by the eProsima Micro XRCE-DDS library and how it can be configured and customized by the user. For more information regarding the internal handling of the memory in eProsima Micro XRCE-DDS, refer to the detailed analysis and memory profiling here.

Executable code size

To tune the executable code size, the library can be compiled enabling or disabling several profiles. To add or remove profiles from the library, enable or disable them as CMake arguments. More information can be found at: eProsima Micro XRCE-DDS Client.

Important

When compiling with gcc, it is highly recommended to compile it with the linker flag: -Wl,--gc-sections. It will remove the code that the app doesn’t use from the final executable.

Runtime size

The Client is dynamic and static memory free: the whole memory footprint only depends on how the stack grows during the execution. Several values can be modified to control the stack growth:

Stream buffers

Streams number

It’s possible to define a maximum of 127 best-effort streams and of 128 reliable streams. However, for most purposes, only one stream - either best effort or reliable - is needed.

History of a reliable stream

The history is used for recovering lost messages and for speeding up the communication. For output streams, a bigger history will allow writing and sending more messages without having to wait for confirmation. However, if the history of an output stream is full (no messages confirmed by the Agent yet), no more messages can be stored in the stream. For input streams, the history is used for recovering lost messages faster while reducing the bandwidth. If the connection is highly reliable and saving memory is a priority, a reduced history can be used.

Stream size

In case of reliable communciation, this size is equal to MAX_MESSAGE_SIZE * HISTORY. In case of a best-effort stream, the size simply equals MAX_MESSAGE_SIZE, as no history is made available in this case. The MAX_MESSAGE_SIZE represents the maximum message size that can be sent without fragmenting the message, and it must be less or equal than the MTU chosen for the selected transport.

MTU

A different MTU can be chosen for each transport available. The MTU value can be defined as a CMake argument, and fixes the MAX_MESSAGE_SIZE that can be sent or received. The transport uses the MTU value to create an internal buffer.