[LUCENE-7639] Use Suffix Arrays for fast search with leading asterisks

• Type: Improvement
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Lucene Fields: New, Patch Available
• Assignee: Unassigned
• Reporter: Yakov Sirotkin
• Created: 17/Jan/17 12:41
• Updated: 28/Aug/22 15:09

Description

If query term starts with asterisks FST checks all words in the dictionary so request processing speed falls down. This problem can be solved with Suffix Array approach. Luckily, Suffix Array can be constructed after Lucene start from existing index. Unfortunately, Suffix Arrays requires a lot of RAM so we can use it only when special flag is set:

-Dsolr.suffixArray.enable=true

It is possible to speed up Suffix Array initialization using several threads, so we can control number of threads with

-Dsolr.suffixArray.initialization_treads_count=5

This system property can be omitted, the default value is 5.

Attached patch is the suggested implementation for SuffixArray support, it works for all terms starting with asterisks with at least 3 consequent non-wildcard characters. This patch do not change search results and affects only performance issues.

Update
suffix-arra-2.patch is an improved version of the first patch, system properties for it are following::

lucene.suffixArray.enable - true, if you want to enable Suffix Array support. Default value - false.
lucene.suffixArray.initializationThreadsCount - number of threads for Suffix Array initialization, if you set 0 - no additional threads used. Default value - 5.

Issue Links

• is related to: LUCENE-7863 Don't repeat postings (and perhaps positions) on ReverseWF, EdgeNGram, etc
• links to: My (mkhl) humble idea for this