DataSource set as readOnly still allows mutable transactions

[Nahuel92]

Hi guys!

I ran into a very odd issue that I would like to share to see if it's my mistake, or if the framework is not intended for the way I'm using it.

I'm conditionally setting a DataSource as readOnly or not based on the value of a few properties via a BeanCreatedEventListener<DatasourceConfiguration> listener (thanks Graeme for this suggestion).

This works really well for single-threaded code, but when using multiple threads I noticed that this configuration is not honored, and write transactions are executed and the readOnly flag is silently ignored.

In any case, I created a PoC app that you can find below. This application sets the readOnly flag to true, to expose this behavior I described above:

https://github.com/Nahuel92/poc-projects/tree/master/micronaut/micronaut-data-multithreading-bug

I also did an ad hoc test with a BeanCreatedEventListener<TransactionManagerConfiguration> listener to set enforceReadOnly to true (in addition to setting the readOnly flag previously mentioned), but without any luck.

If more information is needed, please let me know.

I'll appreciate any clarification/help on this, thanks in advance!

[dstepanov]

It's probably database / driver related. Check if your data are saved.

[Nahuel92]

Hi dstepanov!

Yes, data is saved. I verified this with Postgres. I pushed a new test that passes when it should fail, and it verifies that the data is saved as if the DataSource wasn't set to readOnly mode.

[dstepanov]

It would be better to try some basic JDBC. without any Micronaut

[Nahuel92]

Thanks. I checked and the culprit is the Postgres driver. It has a not-so-clear behavior when readOnly is set.
Either autoCommit needs to be disabled, or readOnlyMode should be set to always:

https://github.com/pgjdbc/pgjdbc/blob/master/pgjdbc/src/main/java/org/postgresql/PGProperty.java#L529

Thanks a lot!