Similar, but different requirements. All of the messages were grouped by sending process, and when the sending process said its session was over its messages we

Similar, but different requirements. All of the messages were grouped by sending process, and when the sending process said its session was over its messages were fed into a post-processing queue. There was support for holding messages in memory or on disk, and data-preserving fallbacks if the post-processing halted or got too backed up. The message rate varied quite a bit; during the US business day the rate was at least doubled. We used that to give the post-processing queue time to catch up off-hours. This was designed about 16 years ago, so well before the big-data tools, ssds, or powerful machines we have today.