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QOS history depth

Playing around with QOS depths, I noticed you can set the depth to 0.
Not sure if that’s allowed? Will it really set it to 0, or does it just force it to 1 in the DDS layer?
I couldn’t tell a difference between a depth of 1 and 0, but maybe I just didn’t test the right combo of Pub/Sub to see a difference.

Playing with the OpenSplice demo_ishapes executable, they don’t even allow a depth size of 0.

I believe that is a special (“reserved”) value that indicates that it should use the system default depth:

Where the system default may be influenced by some global configuration file or something. In fact you can see that we have a condition in each of our implementations to handle this, for example in our fast rtps code: