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From "Matt Schraeder" <>
Subject Syncing lucene index with a database
Date Thu, 26 Mar 2009 22:28:57 GMT
I'm new to Lucene and just beginning my project of adding it to our web
app.  We are indexing data from a MS SQL 2000 database and building
full-text search from it.
Everything I have read says that building the index is a resource heavy
operation so we should use it sparingly.  For the most part the database
table we are working from is updated once a day so as soon as the table
itself is updated we can rebuild our Lucene indexes.  However, there are
a few feilds that get updated with a cronjob every 15 minutes.  In terms
of speed and efficiency, what would be a better system for keeping our
data synced between the database and Lucene?
Of course one option would be to rebuild the Lucene index each time the
cronjob runs to keep the database and Lucene index synced.  We could
either return the entire database table, loop through the rows, get a
row's document in lucene remove/readd it, and do that for each row.
Alternatively after we update the main table we return just the rows
that were changed, loop through those and remove/readd them in lucene,
and do that for just the rows that have changed. 
Alternatively I have thought of using Lucene purely for search to
return just the primary key of items from our database table, then query
the database for those items and get the most up to date data from the
database to actually display our search results.  This would let us use
Lucene's superior searching capabilities and searching speed, but would
still require us to pull the data to be displayed from the database.
Another option is that we could do the same, but only return the fields
that could change frequently.  This would use Lucene to store and index
the majority of what is displayed on a search results page, only using
the database to return the 2 or 3 fields that might change in a search
for each row that lucene returns.
I'm honestly not sure what the "proper" choice should be, or if it
really depends on our own test cases.  Is it perfectly okay to run an
index update every 15 minutes? How much difference would it make in
terms of search time to search with lucene AND pull from the database? 
My main issue with searching with lucene but getting the actual data
from the database is that it seems like that would make our current
search system that is entirely database driven to run slower.

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