How to prepare for integration tests which use PostgreSQL's in memory replacement?

I have learned that using an actual database in integration tests slows them down significantly. So, I have to use an in memory database which may significantly increase speed of my integration tests.

I'm using Springboot for application development. How do I configure PostgreSQL for testing purposes? Is there any in memory database which is highly compatible with PostgreSQL's syntax?

If there is none, how should I perform integration tests.