Module fts 

FTS5 full-text search with BM25 ranking.

This module provides search helpers on top of the items_fts FTS5 virtual table defined in super::schema. The FTS5 table is automatically kept in sync with the items table via INSERT/UPDATE/DELETE triggers.

Column Weights (BM25)

Column	Weight	Rationale
title	3.0	Most specific, short, high signal
description	2.0	Detailed context, moderate signal
labels	1.0	Namespace tags, low cardinality

Tokenizer

Porter stemmer + unicode61 tokenizer with prefix indexes on 2 and 3 characters. This supports:

• Stemming: searching “running” matches “run”, “runs”, “runner”
• Prefix search: “auth*” matches “authentication”, “authorize”
• Unicode: full Unicode word-breaking

Performance

Sub-1ms query time at Tier S (≤1k items). FTS5 lookups are O(log N) via the b-tree index and prefix tables.

Constants

BM25_WEIGHT_DESCRIPTION

BM25_WEIGHT_LABELS

BM25_WEIGHT_TITLE

Default BM25 column weights: title=3, description=2, labels=1.

Functions

fts_in_sync

Validate that the FTS5 index is in sync with the items table.

fts_row_count

Return the number of rows in the FTS5 index.

rebuild_fts_index

Rebuild the FTS5 index from the current items table.

search_bm25

Search the FTS5 index with BM25 ranking and column weights.