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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