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https://issues.apache.org/jira/browse/LUCENE-4227?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13419129#comment-13419129
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Michael McCandless commented on LUCENE-4227:
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bq. I do think maybe this class needs some more warnings, to me it seems it
will use crazy amounts of RAM.
I'll add some scary warnings :)
bq. I also am not sure I like the name "Direct"... is it crazy to suggest
"Instantiated"?
It is very much like the old instantiated (though I think its terms dict is
faster than instantiated's)... but I didn't really like the name
"Instanstiated"... I had picked Direct because it "directly" represents the
postings ... but maybe we can find a better name.
I will update MIGRATE.txt to explain how "Direct" (or whatever we name it) is
the closest match if you were previously using Instantiated...
> DirectPostingsFormat, storing postings as simple int[] in memory, if you have
> tons of RAM
> -----------------------------------------------------------------------------------------
>
> Key: LUCENE-4227
> URL: https://issues.apache.org/jira/browse/LUCENE-4227
> Project: Lucene - Java
> Issue Type: Improvement
> Reporter: Michael McCandless
> Assignee: Michael McCandless
> Attachments: LUCENE-4227.patch, LUCENE-4227.patch
>
>
> This postings format just wraps Lucene40 (on disk) but then at search
> time it loads (up front) all terms postings into RAM.
> You'd use this if you have insane amounts of RAM and want the fastest
> possible search performance. The postings are not compressed: docIds,
> positions are stored as straight int[]s.
> The terms are stored as a skip list (array of byte[]), but I packed
> all terms together into a single long byte[]: I had started as actual
> separate byte[] per term but the added pointer deref and loss of
> locality was a lot (~2X) slower for terms-dict intensive queries like
> FuzzyQuery.
> Low frequency postings (docFreq <= 32 by default) store all docs, pos
> and offsets into a single int[]. High frequency postings store docs
> as int[], freqs as int[], and positions as int[][] parallel arrays.
> For skipping I just do a growing binary search.
> I also made specialized DirectTermScorer and DirectExactPhraseScorer
> for the high freq case that just pull the int[] and iterate
> themselves.
> All tests pass.
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