On Thu, Jul 3, 2014 at 3:38 PM, Tom Lane <t...@sss.pgh.pa.us> wrote: > Michael Paquier <michael.paqu...@gmail.com> writes: >> On Wed, Jul 2, 2014 at 5:32 PM, Kyotaro HORIGUCHI >> <horiguchi.kyot...@lab.ntt.co.jp> wrote: >>> Pehaps this is showing that no tidy or generalized way to tell >>> what a page is used for. Many of the modules which have their >>> own page format has a magic value and the values seem to be >>> selected carefully. But no one-for-all method to retrieve that. > >> You have a point here. > > Yeah, it's a bit messy, but I believe it's currently always possible to > tell which access method a PG page belongs to. Look at pg_filedump. > The last couple times we added index access methods, we took pains to > make sure pg_filedump could figure out what their pages were. (IIRC, > it's a combination of the special-space size and contents, but I'm too > tired to go check the details right now.) Yes, that's what the current code does btw, in this *messy* way.
>> For gin, I'll investigate if it is possible to add a identifier like >> GIN_PAGE_ID, it would make the page analysis more consistent with the >> others. I am not sure for what the 8 bytes allocated for the special >> area are used now for though. > > There is exactly zero chance that anyone will accept an on-disk format > change just to make this prettier. Yeah thought so. -- Michael -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
