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From Avi Drissman <avi_driss...@baseview.com>
Subject Advanced timestamp usage (or global value storage)
Date Wed, 25 Aug 2004 14:19:34 GMT
I've used Lucene for a long time, but only in the most basic way. I 
have a custom analyzer and a slightly hacked query parser, but in 
general it's the basic add document/remove document/query documents 
cycle.

In my system, I'm indexing a store of external documents, maintaining 
an index for full-text querying. However, I might be turned off when 
documents are added, and then when I'm restarted, I'm going to need to 
determine the timestamp of the last document added to the index so that 
I can pick up where I left off.

There are three approaches to doing this, two using Lucene. I don't 
know how I would do the two Lucene approaches, or even if they're 
possible.

1. Just keep a file in parallel with the index, reading and writing the 
timestamp of the last indexed document in it. I know how to do this, 
but I don't like the idea of keeping a separate file.

2. Drop a timestamp onto each document as it's indexed. I've attached 
timestamp fields to documents in the past so that I could do range 
queries on them. However, I don't know how to do a query like "the 
document with the latest timestamp" or even if that's possible.

3. Create a dummy document (with some unique field identifier so you 
could quickly query for it) with a field "last timestamp". This is a 
"global value storage" approach, as you could just store any field with 
any value on it. But I'd be updating this timestamp field a lot, which 
means that every time I updated the index I'd have to remove this 
special document and reindex it. Is there any way to update the value 
of a field in a document directly in the index without removing and 
adding it again to the index? The field I'd want to update would just 
be stored, not indexed or tokenized.

Thanks for your help in guiding my exploration into the capabilities of 
Lucene.

Avi

-- 
Avi 'rlwimi' Drissman
avi@baseview.com
Argh! This darn mail server is trunca


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