Try MySQL instead of MariaDB. They have some performance tweaks in version 10 that aren’t present in MariaDB.
Also, tune your MySQL (or MariaDB) server. Make sure all tables use InnoDB. Enable the slow query log and analyze slow queries (there may be missing indices). If there’s a lot of unique queries, increase the query cache size.
The easy approach is to run MySQLTuner after the MySQL or MariaDB server has been up for at least a week, and go through its suggestions.
There shouldn’t be a significant difference in performance between PostgreSQL and MySQL/MariaDB if both have been optimized. Out-of-the-box config isn’t ideal for a production system.