The thing I still don't understand about this patch is why we call RegisterSegmentBoundaryEntry and NotifySegmentsReadyForArchive in XLogInsertRecord.
My model concept of this would have these routines called only in XLogFlush / XLogWrite, which are conceptually about transferring data from in-memory WAL buffers into the on-disk WAL store (pg_xlog files). As I understand, XLogInsertRecord is about copying bytes from the high-level operation (heap insert etc) into WAL buffers. So doing the register/notify dance in both places should be redundant and unnecessary. In the NotifySegmentsReadyForArchive() call at the bottom of XLogWrite, we use flushed=InvalidXLogRecPtr. Why is that? Surely we can use LogwrtResult.Flush, just like in the other callsite there? (If we're covering for somebody advancing FlushRecPtr concurrently, I think we add a comment to explain that. But why do we need to do that in the first place?) -- Álvaro Herrera PostgreSQL Developer — https://www.EnterpriseDB.com/ "The eagle never lost so much time, as when he submitted to learn of the crow." (William Blake)
