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From Daniel Noll <dan...@nuix.com>
Subject Re: "Deleting" documents without deleting them
Date Tue, 16 Mar 2010 23:07:19 GMT
On Tue, Mar 16, 2010 at 20:45, Rene Hackl-Sommer <rene.a.hackl@gmx.de> wrote:
> Hi Daniel,
>
> Unless you have only a few documents and a small index, I don't think never
> calling optimize is going to be a means you should rely upon.
>
> What about if you reindexed the documents you are deleting, adding a field
> <excludeFromSearch> with the value "true"? This would imply that either
>
> 1) all fields are stored, so you may retrieve them from the original doc and
> add them to the new one plus the exclusion field
> 2) or if a lot of fields are only indexed you'd need access to the original
> source. (With limitations it is also possible to reconstruct a field from
> indexed data only, but not generally recommendable)

Unfortunately it also makes the assumption that it's OK for the doc
IDs to shift - in our application this is not the case as we use it to
key to various databases.  So for us, the effects would be like this:
   Relocating one document to the end of the index and marking the
earlier one as fakedeleted => One query to each relevant table to
update that one document
   Deleting a document in order to re-add a fakedeleted version at the
end (implying that merging occurs) => If 100,000 documents shift, up
to 100,000 IDs in each table need to be updated.

(Why don't we use a separate int field?  Because for tables like tags,
it's too slow to do an additional query into Lucene to map the virtual
ID back to the real doc ID when building filters by tag.)

Of course, if it were possible to add one field to a document without
deleting and re-adding it, yes -- then this would be the way to go for
sure.  In fact, if Lucene had the ability to incrementally update a
document in the first place, I would never have needed to embark on
this whole exercise, as I could just update the document I want to
update and move the old fields to new fields.  At some point a
replaceDocument() which maintains doc IDs would be a very nice thing
to have.

> If you need to keep track of which versions belong together, you may need to
> think about how you uniquely identify documents, how this changes between
> versions, and if the update dates might be of any help.

That gives me an idea.  We have a GUID field already, which is
actually for other purposes, but I could go over TermEnum/TermDocs for
that field and build a filter which only matches the last doc for each
term.  Then I don't have to pay for the storage of a filter... but I
guess it will cost to build this filter anyway so I don't know if it's
practical yet.

I guess storing the filter on disk would be an easier way to go, with
the caveat that it will cost a bit to flip bits each time a new
document is fakedeleted.

Daniel


-- 
Daniel Noll                            Forensic and eDiscovery Software
Senior Developer                              The world's most advanced
Nuix                                                email data analysis
http://nuix.com/                                and eDiscovery software

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