Attached is an updated patch addressing your review comments and fixing the concurrency model for the non-concurrent path.
Regarding the items you brought up: 1. Fixed the indnatts vs indnkeyatts issue for generating the ON CONFLICT target. 2. Removed the incorrect regression test comment regarding subqueries.
Regarding the concurrency gap and safety model: In my last email, I mentioned planning to use transaction-level advisory locks to fix the consistency gap. After prototyping it, I had to abandon that approach. Testing revealed that it falls over at scale, quickly hitting `max_locks_per_transaction` limits and causing issues with bulk operations. I worked on this for a while before deciding it wasn't workable.
Instead, I went a different direction. The non-concurrent partial refresh now uses a different two-step strategy:
1. It first executes a `SELECT FROM mv WHERE ... FOR UPDATE` to lock existing rows matching the predicate. This serializes concurrent partial refreshes on overlapping rows while allowing non-overlapping refreshes to proceed in parallel. 2. It then executes a single CTE that evaluates the underlying query, upserts the results into the matview, and deletes rows that no longer match the predicate via an anti-join.
In my testing, this approach had similar performance to the original implementation, but hasn't exhibited the same correctness issues.
