Otis, Looking at your reply again, I have a couple of questions -
"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." 1. If IndexReader takes a snapshot of the index state when opened and then reads the files when searching, what would happen if the files it takes a snapshot of are deleted before the search is performed (as would happen with a reindexing in the period between opening an IndexSearcher and using it to search)? 2. Does a similar potential problem exist when optimising an index, if this combines all the segments into a single file? Many thanks Paul -----Original Message----- From: Paul Mellor [mailto:[EMAIL PROTECTED] Sent: 16 February 2005 17:37 To: 'Lucene Users List' Subject: RE: Concurrent searching & re-indexing But all write access to the index is synchronized, so that although multiple threads are creating an IndexWriter for the same directory and using it to totally recreate that index, only one thread is doing this at once. I was concerned about the safety of using an IndexSearcher to perform queries on an index that is in the process of being recreated from scratch, but I guess that if the IndexSearcher takes a snapshot of the index when it is created (and in my code this creation is synchronized with the write operations as well so that the threads wait for the write operations to finish before instantiating an IndexSearcher, and vice versa) this can't be a problem. -----Original Message----- From: Otis Gospodnetic [mailto:[EMAIL PROTECTED] Sent: 16 February 2005 17:30 To: Lucene Users List Subject: Re: Concurrent searching & re-indexing 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: http://www.lucenebook.com/search?query=concurrent 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. Otis --- Paul Mellor <[EMAIL PROTECTED]> 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) - > > java.io.IOException: couldn't delete _a.f1 > at org.apache.lucene.store.FSDirectory.create(FSDirectory.java:166) > at > org.apache.lucene.store.FSDirectory.getDirectory(FSDirectory.java:135) > at > org.apache.lucene.store.FSDirectory.getDirectory(FSDirectory.java:113) > at org.apache.lucene.index.IndexWriter.<init>(IndexWriter.java:151) > ... > > 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 > > This e-mail and any files transmitted with it are confidential and > intended > solely for the use of the individual or entity to whom they are > addressed. > If you are not the intended recipient, you should not copy, > retransmit or > use the e-mail and/or files transmitted with it and should not > disclose > their contents. In such a case, please notify > [EMAIL PROTECTED] > and delete the message from your own system. 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