H2 Database Engine is primarily used for running application test cases by our development team. When changes are made to our codebase, we run automated test cases, and when the test case involves data manipulation, H2 Database Engine is used instead of a full blown database such as PostgreSQL. H2 Database Engine is lightweight, simple and runs in-memory, which makes it perfect for this use case.
Simple and quick to get started with, and is light weight (only 2MB).
SQL compliant so it compatible with most relational databases.
There really is not a lot to say here as H2 Database Engine is not a general purpose database such as PostgreSQL or MySQL, so it has a niche use case for being an in-memory database, and it is very good at doing that. Perhaps one slight improvement would be some SQL queries that work with MySQL or PostgreSQL do not work with H2 Database Engine, and so if H2 Database Engine is used as an in-memory replacement for testing, that would create false negatives.
If H2 Database Engine can support some NoSQL databases, it would be fantastic.
This really depends on the use case. For an in-memory replacement database for running unit test cases with, H2 Database Engine is an excellent option. However, if you are looking for a general purpose database for your production systems, then H2 Database Engine is not suited for this purpose.
[H2 Database Engine is] being used for two different purposes. One is for running unit tests for application during compilation phase. This application runs is MySQL database normally, but for unit test purposes that is impractical. In compilation phase an in-memory H2 database is constructed and application tests are run against that. Another purpose is a small authentication security web-application that runs in a single instance. In this case some authentication related details are stored in H2 database that is stored to disk.
For running application tests it's well suited. H2 [Database Engine] can replace the real-world database solution for them easily and removes the requirement to set up a a separate database instance just for running unit tests. For using in actual production application one needs to consider scale. H2 is suitable if application runs in single instance and database is located in same machine as a file where that application runs. This means the application shouldn't have a large user base. However it's easy to switch to an actual MySQL instance if the need arises, it's most likely only a configuration change and doesn't require new code.