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From Shai Erera <ser...@gmail.com>
Subject Re: NFS, Stale File Handle Problem and my thoughts....
Date Wed, 20 Jan 2010 14:32:46 GMT
We've worked around that problem by doing two things:
1) We notify all nodes in the cluster when the index has committed (we use
JMS for that).
2) On each node there is a daemon which waits on this JMS queue, and once
the index has committed it reopens an IR, w/o checking isCurrent(). I think
that the isCurrent call is the problematic one, since that's the one that
checks the segments file (but I admit I forgot the details).
2.1) After the reopen is finished (we do some warm up queries as well), we
'release' this reader to search threads.

So no search thread suffers any overhead from opening a reader, because to
them the readers are always open. Calling reopen means calling isCurrent, so
you can protect that code and call it until it succeeds, or if it fails call
IndexReader.open instead. Anyway, that's done on the daemon side, and
therefore does not incur any overhead for searchers. In the worse case,
they'll use a slightly older index than your application intended for.

I don't know if something like that interests the community, to get a module
that provides IndexSearcher instances, and taking care of their refresh w/o
the application needing to worry about it, or write custom code (which I'm
sure a lot of us write .. and probably the same code). If it does, I don't
mind to patch something.

Shai

On Wed, Jan 20, 2010 at 4:05 PM, Sertic Mirko, Bedag
<Mirko.Sertic@bedag.ch>wrote:

> Hi Mike
>
> Thank you for your feedback!
>
> So I would need the following setup:
>
> a) Machine A with custom IndexDeletionPolicy and single IndexReader
> instance
> b) Machine B with custom IndexDeletionPolicy and single IndexReader
> instance
> c) Machine A and B periodically check if the index needs to be reopened, at
> least at 12 o'clock
> d) Machine A runs an Index update and optimization at 8 o'clock, using the
> IndexDeletionPolicy. The IndexDeletionPolicy keeps track of the files to be
> deleted.
> e) On Machine A, the no longer needed files are taken from the
> IndexDeletionPolicy, and deleted at 12:30. At this point the files to be
> deleted should no longer be required by any IndexReader and can be safely
> deleted.
>
> So the IndexDeletionPolicy should be a kind of Singleton, and in fact would
> only be needed on Machine A, as only here index modifications are made.
> Machine B has read only access.
>
> Would this be a valid setup? The only limitation is there is only ONE
> IndexWriter box, and multiple IndexReader boxes. Based on our requirements,
> this should fix very well. I really want to avoid some kind of index
> replication between the boxes...
>
> Regards
> Mirko
>
>
>
> -----Urspr√ľngliche Nachricht-----
> Von: Michael McCandless [mailto:lucene@mikemccandless.com]
> Gesendet: Mittwoch, 20. Januar 2010 14:45
> An: java-user@lucene.apache.org
> Betreff: Re: NFS, Stale File Handle Problem and my thoughts....
>
> Right, you just need to make a custom IndexDeletionPolicy.  NFS makes
> no effort to protect deletion of still-open files.
>
> A simple approach is one that only deletes a commit if it's more than
> XXX minutes/hours old, such that XXX is set higher than the frequency
> that IndexReaders are guaranteed to have reopened.
>
> The TestDeletionPolicy unit test in Lucene's sources has the
> ExperiationTimeDeletionPolicy that you can use (but scrutinize!).
>
> Another alternative is to simply reopen the reader whenever you hit
> Stale file handle (think of it as NFS's means of notifying you that
> your reader is no longer current ;) ).  But, if reopen time is
> potentially long for your app, it's no good to make queries pay that
> cost and the deletion policy is better.
>
> Mike
>
> On Wed, Jan 20, 2010 at 8:29 AM, Sertic Mirko, Bedag
> <Mirko.Sertic@bedag.ch> wrote:
> > Hi@all
> >
> >
> >
> > We are using Lucene 2.4.1 on Debian Linux with 2 boxes. The index is
> > stored on a common NFS share. Every box has a single IndexReader
> > instance, and one Box has an IndexWriter instance, adding new documents
> > or deleting existing documents at a given point in time. After adding or
> > deleting the documents, a IndexWriter.optimize() is called. Every box
> > checks periodically with IndexReader.isCurrent if the index needs to be
> > reopened.
> >
> >
> >
> > Now, we are encountering a "Stale file handle" error on box b after the
> > index was modified and optimized by box a.
> >
> >
> >
> > As far as i understand the problem with NFS is that box b tries to
> > open/access a file that was deleted by box a on the NFS share.
> >
> >
> >
> > The question is now, when are files deleted? Does only the index
> > optimization delete files, or can files be deleted just by adding or
> > removing documents from an existing index?
> >
> >
> >
> > I now that there might be a better setup with Lucene and index
> > replication, but this is an existing application and we cannot change
> > the architecture now. So what would be the best solution?
> >
> >
> >
> > Can I just "change" the way Lucene deletes files? I think that just
> > renaming no longer needed files would be good on NFS. After every
> > IndexReader has reopened the index, the renamed files can be safely
> > deleted, as they are definitely no longer needed. Where would be the
> > hook point? I heard something about IndexDeletionPolicy....
> >
> >
> >
> > Thanks in advance!
> >
> >
> >
> > Mirko
> >
> >
> >
> >
>
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