Nested transactions detection assumes there is only one DB

[mrkam2]

Describe the bug Nested transactions detection checks for *active-tx* variable that is not specific to the DB or connection.

To Reproduce

1. Set *nested-tx* to prohibit.
2. Open two connections to different databases.
3. Create a transaction with the first database.
4. Inside the transaction, create a transaction with the second database. The operation above will fail although these transactions are not nested.

Expected behavior "Nested" transactions over different DBs should be allowed.

[seancorfield]

This is why the default behavior is to assume the developer knows what they are doing. If you are using multiple databases, within a single TX, you can't use this feature to trap unintentional nesting. I'll update the documentation to clarify that.

[mrkam2]

This is why the default behavior is to assume the developer knows what they are doing. If you are using multiple databases, within a single TX, you can't use this feature to trap unintentional nesting. I'll update the documentation to clarify that.

Is old-autocommit = false not a good indicator of already being inside a transaction?

[seancorfield]

@mrkam2 Nope. There are other reasons for disabling auto-commit (some DBs require auto-commit is disabled for certain DDL operations, for example). JDBC is pretty nasty in this respect because a "transaction" is really just a convention for calling .commit or .rollback -- or using savepoints. The *nested-tx* option was only added about a year ago and I originally didn't plan to document it, except as a potential aid to migration. The default behavior of trusting the developer has been the same since next.jdbc was released, over a year prior to that.