Hi @nomassama , welcome to the Community! ?
Thanks for checking out Solace, comparing to NATS and Kafka. Solace has some pretty cool features and functionality (and stability) over them.
Anyhow… that ID that you’re seeing in the PubSub+ Manager GUI is an internal Message Spool ID that’s assigned by the broker when it stores a message in its message spool (i.e. to disk). It’s not a number/identifier you as a client application can really do anything with… it’s assigned by the broker automatically, and not readily available to consumer applications. And if publishing to lots of destinations, then the IDs on a single queue would not be sequential as the incoming messages would be spread across different queues.
It is an 8-byte long, so would take a couple million years at 100,000 msg/s through the broker to roll over.
An 8-byte ID is really not a lot of overhead! And there are a LOT of other IDs, metadata, headers, etc. associated with messages, connected applications, active flows, etc. that the broker keeps track of. I wouldn’t worry too much about it.