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From Chris Hostetter <>
Subject Re: Lucene 4.x -> 5.x: Converting FieldValueFilter to FieldValueQuery
Date Thu, 05 Nov 2015 17:48:53 GMT

: > The fact that you need to index doc values is related to another change in
: > which we removed Lucene's FieldCache and now recommend to use doc values
: > instead. Until you reindex with doc values, you can temporarily use
: > UninvertingReader[1] to have the same behaviour as in Lucene 4.x.
: Is indexing doc values vs. UninvertingReader a space/time tradeoff? Or
: is the general recommendation to index doc values and only resort to an
: UninvertingReader when a full 4.x to 5.x conversion is to costly in
: terms of dev. hours?

Using docValues is going to be better for almost every use case -- it adds 
additional disk space (and some additional time spent building the index) 
but saves a large amount of RAM + time when opening IndexSearchers.

It is essetnailly a more efficient, on disk, version of FieldCache 
constructed hwen building then index instead of "on the fly" the first 
time it's used.


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