Good day! I burned some time to write Java code which tests H2 database transaction behaviour through Spring Data JDBC. Well documented. Nothing particularly complex or groundbreaking, just JUnit tests to experiment with. This may be of interest to people who want to do their own tests.
This project contains the tests, along with two other subjects, namely an exercise involving agents who communicate via the H2 database and an exercise that verifies that Java Instants are indeed properly stored and retrieved. What to report on the exploration of transactions: 1. I have been unable to generate the "Phantom Read" phenomenon in isolation level ANSI "REPEATABLE READ" . This may be because H2 preventatively nixes it at that level, where it is supposed to still occur. It's possible, depending on how transactions are implemented. Or I just don't use a predicate that is complex enough. 2. Trying to elicit "Non-Repeatable Read" and "Phantom Read" phenomena at isolation level ANSI "READ COMMITTED", we find that the phenomena are unexpectedly *absent* in ~0.18% of cases, apparently randomly: H2 implements stronger transactions than expected. I *don't* think it is my test code that is the reason, but then again, I'm not sure. 3. There is some problem in Spring Data JDBC "translating" an `org.h2.jdbc.JdbcSQLTimeoutException`, leading to the user code receiving a confusing `org.springframework.transaction.TransactionSystemException` with the message `JDBC rollback failed`. This should probably be fixed at the Spring level. 4. H2 is quite radical in generating "deadlock exceptions" (`org.h2.jdbc.JdbcSQLTransactionRollbackException`). As long as two transaction T1 and T2 were active concurrently, T1 wrote X, then committed and T2 read or wrote _something_ then (after T1's commit), writes X too, a deadlock is detected. If I reflect on what could go wrong in such scenarios, I don't see the reason for throwing. Is H2 just extremely pessimistic/conservative? -- You received this message because you are subscribed to the Google Groups "H2 Database" group. To unsubscribe from this group and stop receiving emails from it, send an email to h2-database+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/h2-database/f09bb626-350d-428d-ae47-a224d47faaf5n%40googlegroups.com.
