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From "Beard, Brian" <Brian.Be...@mybir.com>
Subject RE: Wanting batch update to avoid high disk usage
Date Tue, 24 Aug 2010 13:19:52 GMT
We had a situation where our index size was inflated to roughly double.
It took about a couple of months, but the size eventually dropped back
down, so it does seem to eventually get rid of the deleted documents.

With that said, in the future expungeDeletes will get called once a day
to better manage the size.

If you always optimize down to 1 segment, this problem won't occur. We
had this setting at 5 segments, so that may be why the document
deletions took a while longer. 

I'm not 100% sure, but this also seems dependent on how large the
segments are and what the maxMergeMb limit is. This reclamation may take
longer to happen for segments that essentially have less activity
associated them - they are already large and never get merged due to the
number of optimization segments is greater than 1, and they also are
already at the maxMergeMb limit and never get merged through the normal
indexing process.

-----Original Message-----
From: Anshum [mailto:anshumg@gmail.com] 
Sent: Tuesday, August 24, 2010 12:11 AM
To: java-user@lucene.apache.org
Subject: Re: Wanting batch update to avoid high disk usage

Hi Justin,
Lucene does not reclaim space, each update translates to a deletion
followed
by an addition of a new document. Ideally you could let the index size
bloat
and then expungeDeletes or optimize at the end, unless you want to clean
up
and reclaim the disc space for some reason. Optimize/expungeDeletes() is
when lucene would reclaim deleted document ids and document space.
Though
remember that both these functions are highly I/O intensive and time
consuming at times. Just see if reclaiming space midway is something so
essential.

Moreover, a commit would not impact your issue of reclaiming lost disc
space.

--
Anshum Gupta
http://ai-cafe.blogspot.com


On Tue, Aug 24, 2010 at 9:22 AM, Justin <crynax@yahoo.com> wrote:

> My actual code did not call expungeDeletes every time through the
loop;
> however,
> calling expungeDeletes or optimize after the loop means that the index
has
> doubled in size with all the deleted documents still sitting around.
Or is
> it
> true that Lucene will try to reclaim disk space? I assume a commit
would be
> required at some point.
>
>
>
>
> ----- Original Message ----
> From: Anshum <anshumg@gmail.com>
> To: java-user@lucene.apache.org
> Sent: Mon, August 23, 2010 10:18:36 PM
> Subject: Re: Wanting batch update to avoid high disk usage
>
> Don't bother calling expunge deletes so often, makes no sense.
Instead,
> call
> it once at the end, though, you are calling the optimize method in the
end
> anyways so should take care of itself. there shouldn't be any
difference
> (but degradation in performance) on adding a call to expungedeletes().
>
> --
> Anshum Gupta
> http://ai-cafe.blogspot.com
>
>
> On Tue, Aug 24, 2010 at 4:38 AM, Justin <crynax@yahoo.com> wrote:
>
> > In an attempt to avoid doubling disk usage when adding new fields to
all
> > existing documents, I added a call to IndexWriter::expungeDeletes.
Then
> my
> > colleague pointed out that Lucene will rewrite the potentially large
> > segment
> > files each time that method is called.
> >
> >
> >  reader = writer.getReader();
> >  for (int i=0; i<n; i++) {
> >    Term idTerm = new Term("id", i);
> >    TermDocs termDocs = reader.termDocs(idTerm);
> >    if (termDocs != null && termDocs.next()) {
> >      Document doc = reader.document(termDocs.doc());
> >      doc.add(myfield, value);
> >      writer.updateDocument(idTerm, doc);
> >      //writer.expungeDeletes(true); // BAD: rewrites segment files
each
> > time
> >    }
> >  }
> >  reader.close();
> >  writer.commit();
> >  writer.optimize(true);
> >  writer.close();
> >
> >
> > The following Lucene FAQ response suggests that disk space from
deleted
> > documents will be reclaimed. Is this true and is the savings
worthwhile
> to
> > update an existing index (followed by optimizing out the deleted
> documents)
> > instead of simply creating a new index?
> >
> >
> >
>
http://wiki.apache.org/lucene-java/LuceneFAQ#If_I_decide_not_to_optimize
_the_index.2C_when_will_the_deleted_documents_actually_get_deleted.3F
> >F
> >
> >
> > Thanks for your help,
> > Justin
> >
> >
> >
> >
> >
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> >
>
>
>
>
>
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