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From "Michael McCandless (JIRA)" <>
Subject [jira] Commented: (LUCENE-2186) First cut at column-stride fields (index values storage)
Date Fri, 26 Nov 2010 11:22:15 GMT


Michael McCandless commented on LUCENE-2186:

bq. BTW. it is ok to have the same name as a existing field.

It is, usually... but we should add a test to assert this is still the
case for other field + ValuesField?

bq. I'm thinking it's really important now to carry over the same FieldInfos from the last
segment when opening the writer (LUCENE-1737)... because hitting that IllegalStateExc during
merge is a trap.

I think that should not block us from moving forward and landing on trunk ey?

It makes me mighty nervous though... I'll try to get that issue done

Well it is a nice way of extending field but I am not sure if we
should keep it since it is heavy weight. 

The ValuesAttr for ValuesField is actually really heavyweight.  Not
only must it fire up an AttrSource, but then ValuesAttrImpl itself has
a field for each type.  Worse, for the type you do actually use, it's
then another object eg FloatsRef, which in turn holds
array/offset/len, a new length 1 array, etc.

Maybe we shouldn't use attrs here?  And instead somehow let
ValuesField store a single value as it's own private member?

FloatsRef, LongsRef are missing the ASL header.  Maybe it's time to
run RAT :)

> First cut at column-stride fields (index values storage)
> --------------------------------------------------------
>                 Key: LUCENE-2186
>                 URL:
>             Project: Lucene - Java
>          Issue Type: New Feature
>          Components: Index
>            Reporter: Michael McCandless
>            Assignee: Simon Willnauer
>             Fix For: CSF branch, 4.0
>         Attachments: LUCENE-2186.patch, LUCENE-2186.patch, LUCENE-2186.patch, LUCENE-2186.patch,
> 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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