[joshrivers]

Very good question. The answer is, of course, 'it depends'.

What is depends on is how much horizontal scale you expect to have. At a small scale, you can use something like postgres as a centralized broker of sequence. A single postgres cluster can sequence a lot of records in a hurry, no problem.

At a larger scale you might need to decompose your domain into multiple, independently ordered aggregates. Now you have multiple choke point brokers, each of which can handle a lot of records, but which don't block each other.

Step it up another notch, you can use a consensus algorithm (paxos or raft) to get a cluster of machines to agree on the state of the sequence, and perform optimizations such as assigning blocks of sequence by shard and node.

I recommend not over building your event storage architecture until you measure your actual needs. There are cheap ways and huge expensive ways, and building too much is an easy way to make your project fail. Also, one of the nice things about a sequenced set of events is that it is pretty easy to replay into your new, faster event storage later once you've had the happy problem of too much success.