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From Otis Gospodnetic <>
Subject Re: Concurrent searching & re-indexing
Date Wed, 16 Feb 2005 17:30:15 GMT
Hi Paul,

If I understand your setup correctly, it looks like you are running
multiple threads that create IndexWriter for the ame directory.  That's
a "no no".

This section (first hit) describes all various concurrency issues with
regards to adds, updates, optimization, and searches:

IndexSearcher (IndexReader, really) does take a snapshot of the index
state when it is opened, so at that time the index segments listed in
segments should be in a complete state.  It also reads index files when
searching, of course.


--- Paul Mellor <> wrote:

> Hi,
> I've read from various sources on the Internet that it is perfectly
> safe to
> simultaneously search a Lucene index that is being updated from
> another
> Thread, as long as all write access to the index is synchronized. 
> But does
> this apply only to updating the index (i.e. deleting and adding
> documents),
> or to a complete re-indexing (i.e. create a new IndexWriter with the
> 'create' argument true and then re-add all the documents)?
> I have a class which encapsulates all access to my index, so that
> writes can
> be synchronized.  This class also exposes a method to obtain an
> IndexSearcher for the index.  I'm running unit tests to test this
> which
> create many threads - each thread does a complete re-indexing and
> then
> obtains an IndexSearcher and does a query.
> I'm finding that with sufficiently high numbers of threads, I'm
> getting the
> occasional failure, with the following exception thrown when
> attempting to
> construct a new IndexWriter (during the reindexing) -
> couldn't delete _a.f1
> at
> at
> at
> at org.apache.lucene.index.IndexWriter.<init>(
> ...
> The exception occurs quite infrequently (usually for somewhere
> between 1-5%
> of the Threads).
> Does the IndexSearcher take a 'snapshot' of the index at creation? 
> Or does
> it access the filesystem whilst searching?  I am also synchronizing
> creation
> of the IndexSearcher with the write lock, so that the IndexSearcher
> is not
> created whilst the index is being recreated (and vice versa).  But do
> I need
> to ensure that the IndexSearcher cannot search whilst the index is
> being
> recreated as well?
> Note that a similar unit test where the threads update the index
> (rather
> than recreate it from scratch) works fine, as expected.
> This is running on Windows 2000.
> Any help would be much appreciated!
> Paul
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