Rails - Jan 2009 - Nested sets, threads, and trees

Hi everyone!

This may be more a database question than a Rails question, but here
goes.  I have a few questions about implementing tree structures in my
Rails app. It looks like I''ll run into performance issues any way I
slice it, so I''d love to kick around options with people who have
actually done this before.

The situation is this: I have an application where users can create
items.  Each item has a record in the items table.  Although users
cannot edit items created by others, they *can* create a variant of
another user''s item (kind of like forks on GitHub) and edit that.  And
variants can spawn their own variants.  This means that there is a
tree structure of items and their variants:

Item 1 (by Joe)
  |- Item 1 variant A (by Bob)
  |  ''- Item 1 variant A1 (by Alice)
  ''- Item 1 variant B (by Mary)

Item 2 (by Alice)
  ''- Item 2 variant (also by Alice)

If the app takes off, there could potentially be thousands of nodes,
and I can expect both node creation and tree retrieval to be quite
frequent.  Therefore, I am trying to find a structure where it is not
too expensive to show an item and all its descendants, but where it''s
also not too expensive to create a new item.

Right now, I''m using acts_as_tree, which makes it very cheap to add a
new node to the tree, but appears to also make it expensive to get a
list of an item''s descendants.  I''m considering switching to a
nested-
set-based approach (probably BetterNestedSet at
http://opensource.symetrie.com/api/better_nested_set/ ), but while
this would make tree retrieval extremely cheap, I am worried about
having to change all records in the database each time a node is
added.  Does anyone have any thoughts on which way to go here?  It
looks a bit like I''m damned if I do and damned if I don''t.

Thanks,
--
Marnen Laibow-Koser
marnen-sbuyVjPbboAdnm+yROfE0A@public.gmane.org
http://www.marnen.org
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On Jan 26, 1:04 pm, Marnen Laibow-Koser
<mar...-sbuyVjPbboAdnm+yROfE0A@public.gmane.org>
wrote:
> Hi everyone!
>
> This may be more a database question than a Rails question, but here
> goes.  I have a few questions about implementing tree structures in my
> Rails app. It looks like I''ll run into performance issues any way
I
> slice it, so I''d love to kick around options with people who have
> actually done this before.
[...]

Update: I am now using awesome_nested_set .  It works fine for the
moment, but I''d really like to get a nested-interval system working so
that writes won''t be so expensive.  Unfortunately,
acts_as_nested_interval doesn''t work properly at the moment, and I
don''t really want to take the time to patch it at this point (although
I certainly might in future...if nothing else, it would be a very
interesting exercise).  Does anyone know of any other nested-interval
plugins for Rails?  Or should I just wait and patch
acts_as_nested_interval when the time comes?

Best,
--
Marnen Laibow-Koser
marnen-sbuyVjPbboAdnm+yROfE0A@public.gmane.org
http://www.marnen.org
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