HHH-19708 prototype support for read/write replicas

[gavinking]

Rebase of #10754

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https://hibernate.atlassian.net/browse/HHH-19708

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[gavinking]

I have run into a problem here. The session often releases the connection back to the ConnectionProvider before the transaction is complete. But the Postgres driver doesn't like us calling setReadOnly() while the tx is still in progress.

[beikov]

Did you try moving the readOnly reset to org.hibernate.resource.jdbc.internal.AbstractLogicalConnectionImplementor#afterTransaction already?

[gavinking]

Did you try moving the readOnly reset to org.hibernate.resource.jdbc.internal.AbstractLogicalConnectionImplementor#afterTransaction already?

I was looking at that option but then I realized I had kinda misdiagnosed the problem. The problem was really in the case when I didn't start any tx at all. OTOH, I'm not sure how much I care about that case. Seems to work when I do start/end a tx.

[gavinking]

I think this is now a good-enough start to be useful for people to play around and experiment with.

Everything is marked @Incubating, and I'm not really committed to anything about the current design, and I'm totally open to changing it completely if we receive negative feedback about it. But because of the nature of this, it's going to be pretty hard to get any useful feedback before someone actually tries it out in the wild.

So I'm going to merge this. There's absolutely nothing here which is hard to roll back.