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https://issues.apache.org/jira/browse/LUCENE-843?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12492655
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Marvin Humphrey commented on LUCENE-843:
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How are you writing the frq data in compressed format? The works fine for
prx data, because the deltas are all within a single doc -- but for the freq
data, the deltas are tied up in doc num deltas, so you have to decompress it
when performing merges.
To continue our discussion from java-dev...
* I haven't been able to come up with a file format tweak that
gets around this doc-num-delta-decompression problem to enhance the speed
of frq data merging. I toyed with splitting off the freq from the
doc_delta, at the price of increasing the file size in the common case of
freq == 1, but went back to the old design. It's not worth the size
increase for what's at best a minor indexing speedup.
* I've added a custom MemoryPool class to KS which grabs memory in 1 meg
chunks, allows resizing (downwards) of only the last allocation, and can
only release everything at once. From one of these pools, I'm allocating
RawPosting objects, each of which is a doc_num, a freq, the term_text, and
the pre-packed prx data (which varies based on which Posting subclass
created the RawPosting object). I haven't got things 100% stable yet, but
preliminary results seem to indicate that this technique, which is a riff
on your persistent arrays, improves indexing speed by about 15%.
> 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
> Assigned To: Michael McCandless
> Priority: Minor
> Attachments: LUCENE-843.patch, LUCENE-843.take2.patch,
> LUCENE-843.take3.patch, LUCENE-843.take4.patch, LUCENE-843.take5.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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