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From mark harwood <markharw...@yahoo.co.uk>
Subject Re: Incremental Field Updates
Date Mon, 29 Mar 2010 08:35:36 GMT
>I can delete by lucene-generated docId. 


Which users used to have to find by first coding a primary-key-term search. Delete by term
removed this step to make life easier.


>If someone needs this, it can be built over lucene, without
>introducing it as a core feature and needlessly complicating things.

I think with any partial-update feature the *absence* of primary key support would  "needlessly
complicate things":
If Lucene is not capable of performing duplicate detection on insert (because it has no notion
of a primary key field), we need to be prepared for the situation where we have duplicate-key
docs in the index.
What then happens when Grant wants to do a "partial update" as opposed to the existing full-update
semantics which first deletes all documents containing the supplied term (always a form of
primary key)? 
Which document instance gets "partially updated"? We either:
a) throw a "duplicate" error (which ideally should have happened back at dup insert time)
b) Choose one of the documents to "partially update" and keep the duplicate(s)
c) Choose one of the documents to "partially update" and delete the duplicate(s)
d) "Partially update" all of the duplicate(s)
All less than ideal.

I know we are schema-averse with Lucene (and I value that) but surely any partial update feature
has to start with a strongly maintained notion of document identity as a foundation?
Rather than "needless complexity" I'd argue this was "needed rigour" and actually simplifies
the user's job if Lucene can do the duplicate-key-on-insert check automatically rather than
relying on ropy application code and dealing with any failures in that.
Of course primary keys are not mandatory. You only use them when you need this behaviour -
just like in SQL.

Cheers
Mark


      


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