[dunno7456]

Creating a series of connections very quickly is cheaper in MySQL and MariaDB than in PostgreSQL. Typically, a connection poller is used before PostgreSQL to support connection scalability.

I'm not sure if there has been a recent breakthrough that has changed that. I think that still applies today. Correct me if I'm wrong.

[gabereiser]

You can create a series of connections in postgres just as fast. The connection pooler you are referring to is when you put pgBounce or pgPool in between your pgdb and your client software to expand beyond the physical limits of connections and optimize clustered architectures. MySQL at scale is replication only. A few commercial offerings for MySQL like planetscale have brought MySQL into the 21st century. Postgres has a couple ways of clustering, sharding, scaling, beyond your Wordpress database.