[LUCENE-5159] compressed diskdv sorted/sortedset termdictionaries

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 4.5, 6.0
• Component/s: core/index
• Lucene Fields: New
• Assignee: Unassigned
• Reporter: Robert Muir
• Created: 08/Aug/13 17:23
• Updated: 28/Aug/22 13:51
• Resolved: 10/Aug/13 01:16

Description

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).