On 2015-12-10 11:10:10 -0500, Robert Haas wrote: > (More broadly, as Kevin was pointing out to me yesterday, md.c looks > like it could do with a face lift. Keeping a linked list of 1GB > segments and chasing down the list to find the length of the file may > have been fine when relations over 1GB were rare, but that's now > routine. Some relations may be over 1TB, and using a linked list of > 1000 entries to keep track of all of those segments does not seem like > an especially good choice.
Yes, that sucks. I've posted a patch for that at http://archives.postgresql.org/message-id/20141031223210.GN13584%40awork2.anarazel.de - I don't have access to to either the workload or a good testing machine anymore though, so I've kinda lost interest for a while. I'll try to push the patch with the renaming suggested downthread by Tom soonish. > In fact, having no way to get the relation length other than scanning > 1000 files doesn't seem like an especially good choice even if we used > a better data structure. Putting a header page in the heap would make > getting the length of a relation O(1) instead of O(segments), and for > a bonus, we'd be able to reliably detect it if a relation file > disappeared out from under us. That's a difficult project and > definitely not my top priority, but this code is old and crufty all > the same.) The md layer doesn't really know whether it's dealing with an index, or with an index, or ... So handling this via a metapage doesn't seem particularly straightforward. Andres -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
