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From "Erick Erickson" <>
Subject Re: Merging Indeces
Date Mon, 16 Apr 2007 10:18:26 GMT
See below.

On 4/16/07, Moti Nisenson <> wrote:
> Hi,
> I was wondering if the addIndexes() method in IndexWriter can be used for
> updating documents.
> Specifically, I'd like to leave my primary index alone during the update
> process. Instead, I want to use a separate index (on a RAMDirectory), and
> to
> make the updateDocument() calls on it and finally to merge the changes to
> the primary index. This leads to several questions:
> 1) If I make an updateDocument call and the document isn't present in the
> separate index, will it fail?
> 2) After I merge the indeces, will the documents in the primary index be
> updated (i.e. deleted and then added if existing, otherwise just added)?

No, absolutely not. Lucene identifies documents by document ID. All the
documents in your secondary index will get unique Lucene IDs and
Lucene will NOT remove any documents from your original index.

Lucene has no concept of "document identity" in that you can index
the same document 15 times in a row and Lucene will have 15 entries.

3) If the merge does update the primary index, does it all occur in a single
> transaction?

"transaction" is really not a Lucene concept. What kind of behavior are
you really looking for here?

Thanks for the help!
> Moti

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