Write overhead when no subscribers attached

In DDS, data is serialized on write(), not on send.  Data is stored in the DataWriter's send queue in serialized form.  There are lots of reasons for this

1) You don't want to have to serialize the data to send to each DataReader.   DataReaders may be discovered at different times.

2) The same data may need to be send multiple times to the same DataReader...when the connection is RELIABLE, but the network is losing packets.

So, there is a way to avoid the serialization of the data on the call to write().  And that is to use the FlatData "language binding"...which stores the data in serialized form so that when you call write(), there's no additional serialization required.

However, it does require you to define the data type to have the FlatData language binding in IDL and the application to use the FlatData API to manipulate the data structure.  A tradeoff between complexity and performance.

It can certainly help with large/complex data types.  But, probably not as useful for smaller data.

https://community.rti.com/static/documentation/connext-dds/6.0.1/doc/manuals/connext_dds/html_files/RTI_ConnextDDS_CoreLibraries_UsersManual/index.htm#UsersManual/SendingLDFlatData.htm%3FTocPath%3DPart%25203%253A%2520Advanced%2520Concepts%7C23.%2520Sending%2520Large%2520Data%7C23.4%2520FlatData%2520Language%2520Binding%7C_____0

https://community.rti.com/static/documentation/connext-dds/6.0.1/doc/api/connext_dds/api_cpp2/group__RTIFlatDataModule.html

https://community.rti.com/static/documentation/connext-dds/6.0.1/doc/api/connext_dds/api_cpp/group__RTIFlatDataModule.html

Of course, the alternative is to not call write() for your logged data unless there are subscribers.  And you can do that by calling

DataWriter::get_publication_matched_status();

first to check if there are any readers.