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From "Erick Erickson" <>
Subject Re: Design Problem: Searching large set of protected documents
Date Tue, 03 Apr 2007 15:44:09 GMT
Storage isn't too much of a problem, 12.5 M since a Lucene Filter is just
a BitSet, one bit per document. (plus some trivial overhead).

Computational costs... only you know.....

But, is every user allowed individual permissions or are users part of
groups that have permissions? Filters have logical operators (well,
actually it's the bitset that has operators), so you may be able to
save a bunch of time by calculating group permissions
instead and using the relevant AND/OR/NOT operators. Assuming
your permissions are additive, this becomes something like...

Calculate a filter for each group
for each user
   for each group the user is in, or in the relevant group filter
   or in the users individual permissions
   store the filter away.

Then simply add the users filter to a BooleanQuery (MUST)
that you use when you search.

Don't know if this help much or not, but it's an idea <G>.


On 4/3/07, Jonathan O'Connor <> wrote:
> Michael,
> as usual its never so easy! Some users can see almost all documents, and
> some other users can see very few.
> I did find an interesting document that describes the problem (but offers
> no solutions :-()
> This article talks about early and late binding of security information.
> Early binding is faster, but harder to implement. And of course, I
> implemented the easier one.
> I'm going to see what the computational and storage cost will be if I
> precalculate this info.
> Ciao,
> Jonathan O'Connor
> XCOM Dublin
> [image: Inactive hide details for "Michael D. Curtin" <>]"Michael
> D. Curtin" <>
>     *"Michael D. Curtin" <>*
>             03/04/2007 15:28 Please respond to
> To
> cc
> Subject
> Re: Design Problem: Searching large set of protected documents
> Jonathan O'Connor wrote:
> > I have a database of a million documents and about 100 users. The
> documents
> > can have an access control list, and there is a complex, recursive
> > algorithm to say if a particular user can see a particular document.
> >
> > My problem is that my search algorithm is to first do a standard lucene
> > search for matching documents, and then check security on each one
> found,
> > just returning the allowed documents. However, if I do this, and the
> lucene
> > returns 100000 docs, but the user can only see 10 of these, then
> obviously
> > the search is going to take an awful long time.
> >
> > Has anyone come across this problem before, and if so what approach did
> you
> > take? I guess I could precalculate the permissions for every
> user-document
> > pair, but that's alot of storage, and a lot of precalculation!
> My knee-jerk reaction is to suggest a simpler document security model,
> but I'm guessing that that option isn't available to you.
> In your example the security attributes of a document are far more
> discriminating than the query terms.  If that relationship is indicative
> of most of your users and most of the documents, the users and documents
> aren't updated much, and you have a lot of searching to do,
> precalculation (results into an additional document field) seems the way
> to go.  It might even turn out that, if you start from a presumption of
> calculating every user--document security attribute, you come up with an
> algorithm that is much more efficient than a one-off,
> can-this-user-see-this-document type of algorithm.
> Precalculation isn't necessarily a bad thing.  Often, it's quite
> beneficial -- for example, the indexing process itself is a pretty
> substantial precalculation step!
> If this seems unwieldy or impractical for some reason, perhaps you could
> post more attributes of your situation, such as user and data update and
> addition frequency, query attributes and frequency, and so on.
> --MDC
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