As per the original post.
Can somebody point to the documentation where these placeholders usage is described?
I'd be surprised if it is documented. Try <<placeholder>>, or use the composer to insert properties and see how it does it and re-use this pattern.
I mean when you try to add placeholder with composer from service arguments you will get [[Placeholder]]. I'm interested how people know about <<placeholder>>, where do they get this info if there is no documentation about it.
I have seen this behavior be different depending on the underlying database.
Generally speaking most architects need to reverse engineer in order to solve challenges like this. You can look to the JDBC driver documentation, or turn up DB level logging to FINE and see what the DB says, etc.
Thank you for suggestion. In our case we have 'PTC cloud' DB therefore it becomes much more complicated to investigate DB errors. I get my service working, it was just curious if there is some source of information that I'm not aware about)
I see and understand your predicament. Often in those cases, developers will use a non-production license of ThingWorx on their laptop (or Docker) to do the development and then promote validated changes to staging and then production environments. This allows for getting your hands deeper into things like logger levels and other tools like Java Mission Control or VisualVM which you've not be allowed to do on a production environment.