SQLite FTS contains and suffix matches

移动互联 2013-09-03

SQLite is used byDash to search throughdocset indexes. Originally, Dash used LIKE
queries which were fast enough, but became increasingly slower as more docsets were added.

is amazingly fast, but allows only prefix (e.g. query*
) matches by default. For Dash, I needed to persuade it to also perform contains matches (e.g. *query*
) or suffix matches (e.g. *query

How it works

It’s simple, for each term I want to be able to search, I store all of its suffixes.

First of all, the table structure:


Add the term NSString

INSERT INTO searchIndex(suffixes) VALUES("NSString SString String tring ring ing ng g")

Search using suffix queries:

SELECT * FROM searchIndex WHERE suffixes MATCH 'string';

Or contains queries:

SELECT * FROM searchIndex WHERE suffixes MATCH 'str*';


The only downside I could find was that the database got too large. To avoid this, I compress
the data into its actual term.

The compress and uncompress functions behave in this way:

compress("NSString SString String tring ring ing ng g")
-> NSString

-> NSString SString String tring ring ing ng g

This compression reduces the database size to what it would be if only the actual terms were added (without all the suffixes).

Speed results

Searching over 1,110,381 terms (in 102 docsets) using contains queries:

Search for "string" using LIKE:    3.22 seconds
Search for "string" using FTS:     0.18 seconds

Search for "s" using LIKE:         6.87 seconds
Search for "s" using FTS:          0.22 seconds


I chose SQLite FTS because I was already familiar with SQLite and I also needed to work around some Dash-specific edge cases (e.g. how symbols are treated).

Depending on your project, these may be suitable alternatives:

  1. PostgreSQL’s wildspeed module
  2. For OS X or iOS apps: Search Kit

责编内容by:Kapeli Blog (源链)。感谢您的支持!


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