Liquibase transaction rollback vs <rollback> tag

Question

I learned that Liquibase runs each changeSet in a transaction and commits it after inserting into the DATABASECHANGELOG table.

If something goes wrong during the changeSet, the transaction gets rolled back.

My question is, what happens if the changeSet also includes a <rollback> tag. I know that the rollback tags are used in combination with liquibase dedicated rollback commands, but which one has precedence during a regular migration, the command from the rollback tag or the transaction abortion?

Answer 1

The <rollback> block is not used in when an update fails. If the update fails, Liquibase just calls "rollback" on the connection and relies on the database to correctly roll things back. The <rollback> block is only used when doing the separate rollback command where we're "undoing" the changeset that was already committed in the database.

NOTE: the fact that Liquibase relies on the connection rollback to revert a failed update is why you have to be careful if you have multiple statements in the same changeSet. If you have two createTable calls and your the database auto-commits after the first and the second fails, the rollback on the connection will not roll back the first table. So when you run update the next time, you'll get a table already exists error from the first createTable. The rules on exactly what statements auto-commit are database-specific, so the good rule of thumb is "only one statement per changeset"