Gunnar, IN(SELECT ... FROM) is OK for Oracle, you're about IN(1,2,3,4,...1001).
From other side I don't say to make polishing. As you're going to introduce `JdbcMessageGroupStore` we can come back to two tables again and this question goes out quietly.

Mark, Gary, what do you think about this PR and mentioned planned JIRAs?
Should we apply this changes, if we'll definitely eliminate it in the future?