If they're optimized at different times then the document ids could get out of sync, as the optimized version will have deleted documents removed, while the un-optimized one won't.

Also, for add/delete to keep document ids in sync you need to also be sure to use the same mergeFactor.

Doug

Jamie Stallwood wrote:
If you create two parallel indices (to use different parsing methods for
instance), and always add and delete documents in parallel, will the
document ID's always correspond in both indices? And could optimization
destroy any such invariance?



-----Original Message-----
From: Doug Cutting [mailto:[EMAIL PROTECTED]
Sent: 17 November 2003 19:51
To: Lucene Users List
Subject: Re: Which operations change document ids?

Tate Avery wrote:

My first question is: should I steer clear of this all together?


No, I think this is appropriate.


If not, I need to know which Lucene operations can cause document ids to

change.


I am assuming that the following can cause potential changes:
     1) Add document
     2) Optimize index

What else could cause a document id to change?


Nothing.  And even these can only cause an id to change if there have
been deletions.


Could delete provoke a doc id change?


Not when you perform the delete.  Later, when you add to or optimize the
index, the ids for deleted documents are reclaimed.


And, I am assuming that the following DO NOT change the document id:

1) Query the index


That is correct.

Document ids never change with an instance of IndexReader.  When you
open a new index reader you should usually assume that ids have changed.

Doug


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