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From thomasg <>
Subject Lucene Performance Issues
Date Tue, 28 Mar 2006 10:06:54 GMT

Hi, we are currently intending to implement a document storage / search tool
using Jackrabbit and Lucene. We have been approached by a commercial search
and indexing organisation called ISYS who are suggesting the following
problems with using Lucene. We do have a requirement to store and search
large documents and the total document store will be large too. Any comments
on the following would be greatly appreciated.

1) By default, Lucene only indexes the first 10,000 words from each
document. When increasing this default out-of-memory errors can occur. This
implies that documents, or large sections thereof, are loaded into memory.
ISYS has a very small memory footprint which is not affected by document
size nor number of documents.

2) Lucene appears to be slow at indexing, at least by ISYS' standards.
Published performance benchmarks seem to vary between almost acceptable,
down to very poor. ISYS' file readers are already optimized for the fastest
text extraction possible.

3) The Lucene documentation suggests it can be slow at searching and can get
slower and slower the larger your indexes get. The tipping point is where
the index size exceeds the amount of free memory in your machine. This also
implies that whole indexes, or large portions of them, are loaded into
memory. The bigger the index, the more powerful the machine required. ISYS'
search speed is always proportional to the size of the result set. Index
size does not materially affect search speed and the index is never loaded
into memory. It also appears that Lucene requires hands-on tuning to keep
its search speed acceptable. ISYS' indexes are self-managing and do not
require any maintenance to keep them searchable at full speed.

Thanks, Thomas
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