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https://issues.apache.org/jira/browse/LUCENE-843?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12507567
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Doron Cohen commented on LUCENE-843:
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Mike, I am considering testing the performance of this patch on a somewhat
different use case, real one I think. After indexing 25M docs of TREC .gov2
(~500GB of docs) I pushed the index terms to create a spell correction index,
by using the contrib spell checker. Docs here are *very* short - For each index
term a document is created, containing some N-GRAMS. On the specific machine I
used there are 2 CPUs but the SpellChecker indexing does not take advantage of
that. Anyhow, 126,684,685 words==documents were indexed.
For the docs adding step I had:
mergeFactor = 100,000
maxBufferedDocs = 10,000
So no merging took place.
This step took 21 hours, and created 12,685 segments, total size 15 - 20 GB.
Then I optimized the index with
mergeFactor = 400
(Larger values were hard on the open files limits.)
I thought it would be interesting to see how the new code performs in this
scenario, what do you think?
If you too find this comparison interesting, I have two more questions:
- what settings do you recommend?
- is there any chance for speed-up in optimize()? I didn't read your
new code yet, but at least from some comments here it seems that
on disk merging was not changed... is this (still) so? I would skip the
optimize part if this is not of interest for the comparison. (In fact I am
still waiting for my optimize() to complete, but if it is not of interest I
will just interrupt it...)
Thanks,
Doron
> improve how IndexWriter uses RAM to buffer added documents
> ----------------------------------------------------------
>
> Key: LUCENE-843
> URL: https://issues.apache.org/jira/browse/LUCENE-843
> Project: Lucene - Java
> Issue Type: Improvement
> Components: Index
> Affects Versions: 2.2
> Reporter: Michael McCandless
> Assignee: Michael McCandless
> Priority: Minor
> Attachments: index.presharedstores.cfs.zip,
> index.presharedstores.nocfs.zip, LUCENE-843.patch, LUCENE-843.take2.patch,
> LUCENE-843.take3.patch, LUCENE-843.take4.patch, LUCENE-843.take5.patch,
> LUCENE-843.take6.patch, LUCENE-843.take7.patch, LUCENE-843.take8.patch,
> LUCENE-843.take9.patch
>
>
> I'm working on a new class (MultiDocumentWriter) that writes more than
> one document directly into a single Lucene segment, more efficiently
> than the current approach.
> This only affects the creation of an initial segment from added
> documents. I haven't changed anything after that, eg how segments are
> merged.
> The basic ideas are:
> * Write stored fields and term vectors directly to disk (don't
> use up RAM for these).
> * Gather posting lists & term infos in RAM, but periodically do
> in-RAM merges. Once RAM is full, flush buffers to disk (and
> merge them later when it's time to make a real segment).
> * Recycle objects/buffers to reduce time/stress in GC.
> * Other various optimizations.
> Some of these changes are similar to how KinoSearch builds a segment.
> But, I haven't made any changes to Lucene's file format nor added
> requirements for a global fields schema.
> So far the only externally visible change is a new method
> "setRAMBufferSize" in IndexWriter (and setMaxBufferedDocs is
> deprecated) so that it flushes according to RAM usage and not a fixed
> number documents added.
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