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From Simon Willnauer <>
Subject Re: FieldCache future?
Date Thu, 23 Feb 2012 20:22:34 GMT
On Thu, Feb 23, 2012 at 7:41 PM, Robert Muir <> wrote:

> On Thu, Feb 23, 2012 at 1:32 PM, Ryan McKinley <> wrote:
> > In LUCENE-3360, there is discussion that DocValues could be used to
> > replace the existing FieldCache.  This seems like is a great
> > direction, but I am not sure how people see this getting implemented.
> >
> > Is the suggestion to add something like:
> >  DocValues fieldCache(String field);
> > to AtomicReader?
> No, my suggestion is not to add anything to indexreader at all.
> IndexReader is decoupled from FieldCache, I think we should keep it
> that way.

> You can already sort, group, etc on docvalues fields... so I'm arguing
> that users should say up front which fields they are going to
> sort/group on
> so we can actually be an index and compute this stuff at indexing
> time, rather than uninverting at search time (and do this stuff more
> effectively with ideas like LUCENE-3729).

oh man, I am all for this. Opening a big index with FC can put extreme load
on applications while DocValues are almost instant. I think we should cut
over where we can, DV exposes arrays too so runtime perf can't be the issue
here. Plus you can go to disk if you feel comfortable with the perf hit.
Mike had some FST improvements for sorted stuff too as robert mentioned
above (LUCENE-3729)

Thus this "compute/uninvert on the fly" fieldcache could be moved
> somewhere else.

we can have a module for this I think maybe we need a misc module?

> Grouping etc could work solely on a docvalues api and maybe they have
> a special ctor to take a SortedBytes impl (and fieldcache implements
> the docvalues api or some other backwards mechanism).
> This would remove the redundant implementations (both fieldcache and
> DV implementations) in stuff like grouping, join, sort, etc


> Sure its a change, but so is making IndexReader read-only and other
> things we have done.
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