On Mon, 2010-09-27 at 15:07 -0600, David Boreham wrote: > Is the zero_damaged_pages feature expected to work in 8.3.11 ? > > I have a fair bit of evidence that it doesn't (you get nice messages > in saying that the page is being zeroed, but the on-disk data does not > change). > I also see quite a few folk reporting similar findings in various form > and mailing list posts over the past few years. > > I can use dd to zero the on-disk data, but it'd be nice to know > definitively if this feature is expected to work, and if so under > what conditions it might not. It does zero the page in the buffer, but I don't think it marks it as dirty. So, it never really makes it to disk as all-zeros. > fwiw I am enabling zero_damaged_pages using a set command > in a client session, not in the server's config file. The symptoms > I observe are that a query that previously errored out due to > a bad page header error will succeed when zero_damaged_pages > is enabled, the log says that the page is being zeroed. > However the same query run subsequently without zero_damaged_pages > will again fail, and pg_filedump shows that the on-disk data > hasn't changed. The subsequent queries may succeed if the page is still in the buffer cache. zero_damaged_pages is not meant as a recovery tool. It's meant to allow you to pg_dump whatever data is not damaged, so that you can restore into a fresh location. Regards, Jeff Davis -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
