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From Elisiano Petrini <elisi...@gmail.com>
Subject Re: Tree like structures in CouchDB
Date Fri, 22 Feb 2013 07:04:30 GMT
Hi All,
    please forgive me if I'm missing/overlooking something here, I'm not
a couchdb expert.

It all depends on the needs of the project but usually one would want to
trasverse the tree from the root node down to its children.
In every implementation of trees that I've seen (and done) so far, it's
always the parent node knowing which are its children and not the other
way around.

In this particular case (having a structure of messages) I would still
have a list of direct children in the parent but also have a reference
to the parent in a child node in order to easily trasverse the tree in
both directions.

Having only the reference to the parent, how would you effectively
reconstruct the tree? Reading all the documents and then reconstruct the
structure? (or am I missing something here?).

Cheers, Elisiano

On Fri, 2013-02-22 at 19:09 +1300, Michael Heuberger wrote:
> andrey, svilen, many thanks again.
> 
> agreed, storing immediate children in a document is a bad idea. i think 
> i go for storing only an immediate parent id to get an infinite tree depth.
> 
> thanks for your inspirations guys
> 
> cheers
> michael
> 
> On 22/02/13 18:49, Andrey Kuprianov wrote:
> > PS - storing only an immediate parent id would be the solution for an
> > infinite tree depth.
> >
> >
> > On Fri, Feb 22, 2013 at 1:48 PM, Andrey Kuprianov <
> > andrey.kouprianov@gmail.com> wrote:
> >
> >> Storing immediate children in a parent is a bad idea in a sense that you
> >> will never be able to traverse your tree back to the root, given a child
> >> node.
> >>
> >> Storing all in one doc - you will run out of space before you know it.
> >> Documents have a finite length and the larger the document, the slower it
> >> will get to serialize and unserialize it.
> >>
> >> Storing just an immediate parent in children might result in a costly
> >> multiple read operations, if you want to get root of the tree given an
> >> arbitrary child.
> >>
> >> Therefore the only feasible solution is to store references to the parent
> >> chain - i.e. ancestors - starting from an immediate parent and ending with
> >> a tree root.
> >>
> >>
> >> Here's a simple calculation for ancestors approach:
> >>
> >> Suppose the maximum document size is 1MB. A uuid is 32 characters in
> >> length + taking into account commas and brackets, then the depth of your
> >> tree (I am not taking content into account) could be roughly:
> >>
> >> ((32 + 1)*n  + 2 - 1) = 1024 * 1024  ==> n = 31775 levels
> >>
> >> However, max document size is configurable from the settings (as of
> >> CouchDB 1.2) and could easily be up to 4GB, giving you over 130mil of
> >> levels. Should be enough... :)
> >>
> >>
> >>
> >> On Fri, Feb 22, 2013 at 1:14 PM, Michael Heuberger <
> >> michael.heuberger@binarykitchen.com> wrote:
> >>
> >>> thanks andrey and svil
> >>>
> >>> depth is infinite. in theory a message can have million replies forth and
> >>> back. similar like a very long email thread.
> >>>
> >>> i think storing ancestors ą la andrey would be too much hassle but works
> >>> well for few levels.
> >>>
> >>> svil, what did you mean with dicts and with keeping all children in one
> >>> doc? can you tell me more?
> >>>
> >>> thanks,
> >>> michael
> >>>
> >>>
> >>> On 22/02/13 17:27, svilen wrote:
> >>>
> >>>> my rough guess:
> >>>>
> >>>> if it's finite depth, then all in one doc:
> >>>> - list of (item or (list of ...))
> >>>> - or same with dicts
> >>>>
> >>>> else, one doc per message keeping just link-to-parent,
> >>>> or multiple links-to-grand...grand-parents and/or root.
> >>>> similar to the strategies in SQL - nested etc.
> >>>> keeping all chidlren of same node in one doc is also possible..
> >>>>
> >>>> in any case either traversal or storing or both will be
> >>>> difficult.
> >>>>
> >>>> ciao
> >>>> svil
> >>>>
> >>>> On Fri, 22 Feb 2013 17:13:01 +1300
> >>>> Michael Heuberger <michael.heuberger@**binarykitchen.com<michael.heuberger@binarykitchen.com>>
> >>>> wrote:
> >>>>
> >>>>   Hello guys
> >>>>> I'd like to store messages in a tree like structure. Whenever you
> >>>>> reply to a message, then the original message becomes the parent
> >>>>> message.
> >>>>>
> >>>>> How would you implement something like this in CouchDB? Just curious
> >>>>> and need a little guidance + advice here.
> >>>>>
> >>>>> Thanks,
> >>>>> Michael
> >>>>>
> >>>>> --
> >>>>>
> >>>>> Binary Kitchen
> >>>>> Michael Heuberger
> >>>>> 4c Dunbar Road
> >>>>> Mt Eden
> >>>>> Auckland 1024
> >>>>> (New Zealand)
> >>>>>
> >>>>> Mobile (text only) ...  +64 21 261 89 81
> >>>>> Email ................  michael@binarykitchen.com
> >>>>> Website ..............  http://www.binarykitchen.com
> >>>>>
> >>>>>
> >>> --
> >>>
> >>> Binary Kitchen
> >>> Michael Heuberger
> >>> 4c Dunbar Road
> >>> Mt Eden
> >>> Auckland 1024
> >>> (New Zealand)
> >>>
> >>> Mobile (text only) ...  +64 21 261 89 81
> >>> Email ................  michael@binarykitchen.com
> >>> Website ..............  http://www.binarykitchen.com
> >>>
> >>>
> 



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