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List:       solr-dev
Subject:    [jira] Commented: (LUCENE-2186) First cut at column-stride fields
From:       "Michael McCandless (JIRA)" <jira () apache ! org>
Date:       2010-06-30 10:15:51
Message-ID: 21917514.131031277892951283.JavaMail.jira () thor
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Michael McCandless commented on LUCENE-2186:
--------------------------------------------

Great -- thanks for pushing this forward Simon!

bq. Mike do you mind if I take this?

Please do!

> First cut at column-stride fields (index values storage)
> --------------------------------------------------------
> 
> Key: LUCENE-2186
> URL: https://issues.apache.org/jira/browse/LUCENE-2186
> Project: Lucene - Java
> Issue Type: New Feature
> Components: Index
> Reporter: Michael McCandless
> Assignee: Michael McCandless
> Fix For: 4.0
> 
> Attachments: LUCENE-2186.patch, LUCENE-2186.patch, LUCENE-2186.patch, mem.py
> 
> 
> I created an initial basic impl for storing "index values" (ie
> column-stride value storage).  This is still a work in progress... but
> the approach looks compelling.  I'm posting my current status/patch
> here to get feedback/iterate, etc.
> The code is standalone now, and lives under new package
> oal.index.values (plus some util changes, refactorings) -- I have yet
> to integrate into Lucene so eg you can mark that a given Field's value
> should be stored into the index values, sorting will use these values
> instead of field cache, etc.
> It handles 3 types of values:
> * Six variants of byte[] per doc, all combinations of fixed vs
> variable length, and stored either "straight" (good for eg a
> "title" field), "deref" (good when many docs share the same value,
> but you won't do any sorting) or "sorted".
> * Integers (variable bit precision used as necessary, ie this can
> store byte/short/int/long, and all precisions in between)
> * Floats (4 or 8 byte precision)
> String fields are stored as the UTF8 byte[].  This patch adds a
> BytesRef, which does the same thing as flex's TermRef (we should merge
> them).
> This patch also adds basic initial impl of PackedInts (LUCENE-1990);
> we can swap that out if/when we get a better impl.
> This storage is dense (like field cache), so it's appropriate when the
> field occurs in all/most docs.  It's just like field cache, except the
> reading API is a get() method invocation, per document.
> Next step is to do basic integration with Lucene, and then compare
> sort performance of this vs field cache.
> For the "sort by String value" case, I think RAM usage & GC load of
> this index values API should be much better than field caache, since
> it does not create object per document (instead shares big long[] and
> byte[] across all docs), and because the values are stored in RAM as
> their UTF8 bytes.
> There are abstract Writer/Reader classes.  The current reader impls
> are entirely RAM resident (like field cache), but the API is (I think)
> agnostic, ie, one could make an MMAP impl instead.
> I think this is the first baby step towards LUCENE-1231.  Ie, it
> cannot yet update values, and the reading API is fully random-access
> by docID (like field cache), not like a posting list, though I
> do think we should add an iterator() api (to return flex's DocsEnum)
> -- eg I think this would be a good way to track avg doc/field length
> for BM25/lnu.ltc scoring.

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