Martijn van Oosterhout írta:
On Mon, May 19, 2008 at 08:19:17AM +0200, Zoltan Boszormenyi wrote:
The standard has a clause to specify depth-first order. However doing a
depth-first traversal would necessitate quite a different looking plan and
it's far less obvious (to me anyways) how to do it.
That would be even cooler to have it implemented as well.


From an implementation point of view, the only difference between
breadth-first and depth-first is that your tuplestore needs to be LIFO
instead of FIFO.

Are you sure? I think a LIFO tuplestore would simply return reversed
breadth-first order. Depth-first means for every new record descend into
another recursion first then continue with the next record on the right.

However, just looking at the plan I don't know whether
it could support that kind of usage. At the very least I don't think
the standard tuplestore code can handle it.


--
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Zoltán Böszörményi
Cybertec Schönig & Schönig GmbH
http://www.postgresql.at/



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