Robert Haas <robertmh...@gmail.com> writes: > As far as I can tell, there are basically two viable solutions on the > table here.
> 1. Every time we observe a page as all-visible, (a) set the > PD_ALL_VISIBLE bit on the page, without bumping the LSN; (b) set the > bit in the visibility map page, bumping the LSN as usual, and (c) emit > a WAL record indicating the relation and block number. On redo of > this record, set both the page-level bit and the visibility map bit. > The heap page may hit the disk before the WAL record, but that's OK; Um, no it isn't. Suppose the heap page gets to disk but we crash before the WAL record does. Now we have a persistent state where the heap page is marked PD_ALL_VISIBLE but the corresponding VM bit is not set. The VM bit will never become set, either, because operations on the heap page will see PD_ALL_VISIBLE and assume it already is set. This state of affairs might be acceptable from a correctness standpoint, but not from a performance standpoint. regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers