On Sat, Mar 23, 2013 at 7:25 AM, Alan Woodward <[email protected]> wrote:
>> I think instead FieldCache should actually be completely package
>> private and hidden behind a UninvertingFilterReader and accessible via
>> the existing AtomicReader docValues methods.
>
> Aha, right, because SegmentCoreReaders already caches XXXDocValues instances 
> (without using WeakReferences or anything like that).
>
> I should explain my motivation here.  I want to store various scoring factors 
> externally to Lucene, but make them available via a ValueSource to 
> CustomScoreQueries - essentially a generalisation of FileFloatSource to any 
> external data source.  FFS already has a bunch of code copied from 
> FieldCache, which was why my first thought was to open it up a bit and extend 
> it, rather than copy and paste again.
>
> But it sounds as though a nicer way of doing this would be to create a new 
> DocValuesProducer that talks to the external data source, and then access it 
> through the AR docValues methods.  Does that sound plausible?  Is SPI going 
> to make it difficult to pass parameters to a custom DVProducer (data 
> location, host/port, other DV fields to use as primary key lookups, etc)?
>

its not involved if you implement via FilterAtomicReader. its only
involved for reading things that are actually written into the index.

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