fix: build list FTS indexes as row documents#7656
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| posting_memory_delta += | ||
| new_posting_memory_size as i64 - old_posting_memory_size as i64; | ||
| token_num += 1; | ||
| last_position = Some(position); |
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["want the", "apple"] would be treated as "want apple" with positions [0, 1]
but "want the apple" would be "want apple" with positions [0, 2] (the stop words also contribute to the position increment)
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…igurable Resolves the process_document conflict against the list-FTS restructure (#7656): keep main's DocumentSource/process_text closure shape and thread this branch's posting block_size through the PostingListBuilder construction sites (position closure and the positionless resize_with).
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Summary
Close #5887
Build FTS indexes for list string columns as row-level documents instead of flattening each list element into its own document.
This means
List<Utf8>,List<LargeUtf8>, and theirLargeListvariants now treat a row as one document, with non-null list elements contributing text fragments to that document. Token positions are continuous across list elements, so phrase queries can match across element boundaries.The change intentionally does not add user parameters, persistent metadata, legacy migration, or query-side deduplication. Old list indexes keep their existing behavior.
Context
Issue #5887 reports duplicate FTS results for list string columns because the old index builder treated each list element as a separate document with the same row id. Row-level indexing fixes the result duplication and brings BM25 document statistics back to row-level semantics for newly built indexes.
Follow-up issue #7654 tracks MemWAL in-memory FTS support for list string columns.
Validation
cargo fmt --allgit diff --checkcargo test -p lance-index flat_bm25_searchcargo test -p lance-index test_worker_cargo test -p lance test_fts_listcargo test -p lance test_fts_index_with_cargo clippy -p lance-index --tests -- -D warningscargo clippy -p lance --tests -- -D warnings