On 3/13/19 1:12 PM, Robert Haas wrote: > On Tue, Mar 12, 2019 at 6:54 PM Tomas Vondra > <tomas.von...@2ndquadrant.com> wrote: >> Attached is a patch adopting the dlist approach - it seems to be working >> quite fine, and is a bit cleaner than just slapping another pointer into >> the SMgrRelationData struct. So I'd say this is the way to go. > > What about using a data structure that supports O(1) lookups for any element? > > The current efforts all seem to revolve around correctly guessing from > which end of the list we are likely to delete stuff, but your research > suggests that we don't always make such guesses particularly well. > And it seems unnecessary. >
Isn't the the doubly-linked list is doing exactly that? AFAICS we already maintain a hash table of the smgr relations, and we look them up in this table. We don't need to look them up in the list of unowned relations - the whole problem is that with the current single-linked list, we need to iterate the list anyway to update pointer in the preceding entry. regards -- Tomas Vondra http://www.2ndQuadrant.com PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
