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From Alessandro Benedetti <>
Subject Re: FieldCache?
Date Tue, 06 Oct 2015 10:21:22 GMT
We should make some precision here,
When dealing with faceting , there are currently 2 main approaches :

1) *Enum Algorithm* - best for low cardinality value fields, it is based on
retrieving the term enum for all the terms in the index, and then
intersecting the related posting list with the query result set

2) *Un-Inverting Algorithms* - Best for high cardinality value fields, it
is based on uninverting the index, checking the value for each query result
document field, and counting the occurrences

Within the 2nd approach :

2a) *Doc Values * - It is better for dynamic indexes, built at indexing
time and stored on the disk ( setting the specific attribute for the field)
OR calculated at runtime thanks to the UnInvertedReader that will uninvert
to an in-memory structure that looks like DocValues

2b) *Uninverted field* - for index that changes less frequently . After the
removal related :
Only per segment field caches are available, which means you should be able
to use it using the fcs algorithm.

This should be the current situation,
I will take a look into details and let you know if I understood something


2015-10-06 5:03 GMT+01:00 William Bell <>:

> So the FieldCache was removed from Solr 5.
> What is the implication of this? Should we move all facets to DocValues
> when we have high cardinality (lots of values) ? Are we adding it back?
> Other ideas to improve performance?
> From Mike M:
> FieldCache is gone (moved to a dedicated UninvertingReader in the
> miscmodule).
> This means when you intend to sort on a field, you should index that field
> using doc values, which is much faster and less heap consuming than
> FieldCache.
> --
> Bill Bell
> cell 720-256-8076


Benedetti Alessandro
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