Robert Muir created LUCENE-5159:
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Summary: compressed diskdv sorted/sortedset termdictionaries
Key: LUCENE-5159
URL: https://issues.apache.org/jira/browse/LUCENE-5159
Project: Lucene - Core
Issue Type: Improvement
Components: core/index
Reporter: Robert Muir
Sorted/SortedSet give you ordinal(s) per document, but them separately have a
"term dictionary" of all the values.
You can do a few operations on these:
* ord -> term lookup (e.g. retrieving facet labels)
* term -> ord lookup (reverse lookup: e.g. fieldcacherangefilter)
* get a term enumerator (e.g. merging, ordinalmap construction)
The current implementation for diskdv was the simplest thing that can possibly
work: under the hood it just makes a binary DV for these (treating ordinals as
document ids). When the terms are fixed length, you can address a term directly
with multiplication. When they are variable length though, we have to store a
packed ints structure in RAM.
This variable length case is overkill and chews up a lot of RAM if you have
many unique values. It also chews up a lot of disk since all the values are
just concatenated (no sharing).
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