Exchanges are famous for having to deal with a huge amount of messages. For example, some years (decades?) ago Nasdaq has migrated their reliable UDP protocol from 32-bit, which could support sequence numbers up to 4,294,967,295 to 64-bit, which can now support sequence numbers up to 18,446,744,073,709,551,615.
Some types of messaging middleware solutions are:
Which approach above and/or product (commercial/open source/in-house) are they using it? Is this information known to the tech community?