The Java app relied on 53 database tables, some of which were still MyISAM, and some of which were InnoDB. Only about 10 of them had a lot of data. The database server performed significantly better after an upgrade to Percona Server, but was still showing a load average of about 4-5 during busy times.
The new PostgreSQL schema contained only 13 database tables upon launch, as we determined most of the MySQL tables weren’t in active use. After launch, we had to add some missing indices on tables, and after that the load on the server settled to about 1.5-2 during high-traffic times