In Payara Micro 5, Derby will be removed as default database and replaced with H2. Similar to Derby, H2 is a Java based Database. More info can be found here
Why was Derby Removed
In terms of performance, Derby is one of the slowest embedded databases as compared to H2, PostgresSQL, HSQLDB. H2 also has a smaller disk footprint; the size of a jar file is around 1.5 MB. This should have positive effect on Payara Micro’s boot time.