Should increase writer history depth to fix reader's out of order case.

[advancenXX]

If reliable writer whose depth is 3 sends 4 packages A-B-C-D at the same time, then reader may receive in wrong order like D-A-B-C.
When package D is received, a Heartbeat message shows writer's history has B, C, D, so reader update changes_from_writer_low_mark_ to B, and tell user on_sample_lost.
Then, when package A is received after package D(out of order), package A will not be accepted by fastdds, as,
WriterProxy::change_was_received() {
if (seq_num <= changes_from_writer_low_mark_) {
return true;
}
...
}

So, I find all of package A, B and C will not be accepted by fastdds, and only package D sends on_data_available.
I am wondering if it is the only way to increase writer's depth to 4, so the out of order packages will not be treated as change_was_received.

[JesusPoderoso]

Hi @advancenXX you can either increase writer's depth to a higher value, or modify the QoS to KEEP_ALL instead of KEEP_LAST N.

[advancenXX]

Yes, all I can do now is increase writer's depth. But it is hard for me to choose a reasonable value for the depth, as KEEP_ALL lead to memory problem.
Is there any other way?

[JesusPoderoso]

Yes, you can set the reader as reliable too.