On 2013-07-24 11:26:00 -0400, Tom Lane wrote: > So I went off to implement the SPITupleTable tracking discussed in > <6553.1374424...@sss.pgh.pa.us>, and thought it would be cool to > use the slist infrastructure defined in lib/ilist.h rather than > creating a separate List node for each SPITupleTable struct. > However, I soon ran into a problem: there's no real support for > "remove the current element of an slist while we're scanning it", > which is really the only list manipulation I need. The only way > to remove an element is slist_delete(), which will iterate over > the list *again* and thus create an O(N^2) penalty. Or I could > use a dlist, but two pointers per struct seem pretty silly.
> So I'm going to end up hand-implementing the same kind of manipulation > we frequently use with traditional Lists, namely keep a second variable > that's the preceding list element (not the next one) so I can unlink and > delete the target element when I find it. ilist.h is not offering me > any useful support at all for this scenario. Seems like we're missing > a bet here. Hm. Yes. This should be added. I didn't need it so far, but I definitely can see usecases. slist_delete_current(slist_mutable_iter *)? I am willing to cough up a patch if you want. This will require another member variable in slist_mutable_iter which obviously will need to be maintained, but that seems fine to me since it will reduce the cost of actually deleting noticeably. Greetings, Andres Freund -- Andres Freund http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
