Forget Mr. Celko's work on nested sets - its old stuff. Look for Vadim Tropashko's work on Farey Sequences and Continued Fractions - a much improved way of creating trees with generic SQL.
Richard
Max Pfingsthorn wrote:
Dear Developers,
I was recently looking up different algorithms to store trees in an SQL database. I have found these very interesting articles from 1996.
The author, Joe Celko, writes that trees can be represented as Nested Sets (see the first article for some explanation). I think, this might be useful to Slide's SQL backend and the querying of the WebDAV tree. 'Recursive' searches, i.e. depth=infinity, reduce to mere SELECTs comparing integers rather than making the DB match strings. And, with a little extra, depth=1 is also a simple SELECT. However, inserts are a bit more expensive, which would be fine, however, since in general, the WebDAV repository is not written to so often in comparison to the reads. What do you think about restructuring the SQL to take advantage of this?
For complete reference on the Nested Sets, see: http://www.dbmsmag.com/9603d06.html http://www.dbmsmag.com/9604d06.html http://www.dbmsmag.com/9605d06.html http://www.dbmsmag.com/9606d06.html
In general, I am very interested in optimizing the SQL backend a bit more. I noticed that the LIMIT clause is actually emulated within the backend instead of using the SQL feature. We are using MySQL behind Slide, so that would help us a lot. What do you think about specializing the backend(s) even more to take full advantage of the different vendor-specific implementations? Of course, maintenance would be harder, but it sure would give performance a kick.
Best regards, Max Pfingsthorn
Hippo Oosteinde 11 1017WT Amsterdam The Netherlands
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