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From "Grant Ingersoll (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-762) [PATCH] Efficiently retrieve sizes of field values
Date Fri, 29 Dec 2006 14:53:23 GMT
    [ http://issues.apache.org/jira/browse/LUCENE-762?page=comments#action_12461382 ] 
            
Grant Ingersoll commented on LUCENE-762:
----------------------------------------

Hi Chuck,

I haven't applied this yet, but it looks good.  My only hesitation, and this is no reflection
on how you have implemented it, but the if-then-else structure around line 104 is starting
to get ugly.  I can imagine it growing and growing as more cases are handled.  I was wondering
if maybe we should convert to a map lookup approach.  In Java 1.5 the map would be something
like: 
Map<FieldSelectorResult, FieldSelectorFunctor>

where the Functor does the work of what is in the clause of each of the different cases
then, the if-else structure could be replaced by
FieldSelectorFunctor functor = map.get(FieldSelectorResult);
if (functor != null)
{
    functor.apply(doc, fi, binary, compressed, tokenize);
}
else
{
    skipField(binary, compressed)
}


The constructor/static would be responsible for instantiating the Map.  The Functors could
be implemented as inner classes (although this can lead to a bunch of inner classes too)

What do you think?

> [PATCH] Efficiently retrieve sizes of field values
> --------------------------------------------------
>
>                 Key: LUCENE-762
>                 URL: http://issues.apache.org/jira/browse/LUCENE-762
>             Project: Lucene - Java
>          Issue Type: New Feature
>          Components: Store
>    Affects Versions: 2.1
>            Reporter: Chuck Williams
>         Attachments: SizeFieldSelector.patch
>
>
> Sometimes an application would like to know how large a document is before retrieving
it.  This can be important for memory management or choosing between algorithms, especially
in cases where documents might be very large.
> This patch extends the existing FieldSelector mechanism with two new FieldSelectorResults:
 SIZE and SIZE_AND_BREAK.  SIZE creates fields on the retrieved document that store field
sizes instead of actual values.  SIZE_AND_BREAK is especially efficient if one field comprises
the bulk of the document size (e.g., the body field) and can thus be used as a reasonable
size approximation.

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