Recommended persistence layer for production

[Ruslan]

There was a discussion similar to your question, can be useful

Pros and cons of various database engines

The benefits of Cassandra over MySQL: Replication is seamless. Configuring fully consistent MySQL replication is non trivial if even possible. Ability to scale out by adding DB hosts. Currently, MySQL binding of Temporal doesn’t support sharding. Vitess support will be added in the future. It is more production hardened as Uber has been using Cassandra in production for 4 years. The benefits of MySQL over Cassandra: Simpler operations. More cloud hosted offerings

cc @Wenquan_Xing in case there is anything additional regarding MySQL vs PostgreSQL