“PostgreSQL resolves uniqueness through heap tuple visibility”

I recently commented on Jonathan Lewis’s blog, , ), and to support MongoDB-style multi-key indexing

Oracle's method of keeping uniqueness solely within the index structure is effective for a fixed set of index types. PostgreSQL, on the other hand, distinguishes index navigation from tuple visibility, enabling any index access method to perform MVCC-aware uniqueness checks without having to deal with the MVCC implementation. An open-source, extensible system faces trade-offs: it needs to keep the code simple and manageable, with clear separation of concerns, to support community and ecosystem contributions.