Lagom by default uses Cassandra as a persistence layer, but it also supports other databases like Postgres and MySql. I have not yet tried using anything other than Cassandra. I believe one of the main reasons for Cassandra to be the default choice for Lagom is due to its write performance - event sourcing applications write a lot so write performance really matters.
I once worked in the project that had the business requirement to support something like 1k~3k transactions per second and the team managed to meet that goal with MySql - I am not too sure what exactly was done but we had very experienced db engineers and I was told that they did lots of tunings on the DB itself to support it.
If you are building with Lagom using anything other than Cassandra, I would love to find out your experiences so far.
If you are using MySql or Postgres, have you encountered any performance
issues caused by your messages table getting locked with each write commits?
Recently I am personally looking at the Scylla DB as a drop-in replacement for Cassandra. Nothing really is wrong with Cassandra but I just think it is really too heavy and bit expensive to maintain.