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TiDB vector index: SHOW WARNINGS explains why the ANN index was not used

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TiDB vector index: SHOW WARNINGS explains why the ANN index was not used: : ordering by the wrong distance function gives the warning ANN index not used: not ordering by COSINE distance.

[TiDB docs]: ordering by the wrong distance function gives the warning ANN index not used: not ordering by COSINE distance. Ordering DESC gives ANN index not used: index can be used only when ordering by veccosinedistance() in ASC order. The planner only accepts ascending order, a single ORDER BY item, TopN directly above the DataSource, and no pushed-down filters: a WHERE pre-filter defeats the index. Analyze performance with EXPLAIN ANALYZE and the vector_idx execution info, which shows load, search, and read breakdowns.

Context: When the vector index cannot be used, TiDB emits a warning naming the cause. Check warnings right after EXPLAIN.

Matched source

Source: Source: https://docs.pingcap.com/tidb/dev/vector-search-index/ Original query: "TiDB vector index: SHOW WARNINGS explains why the ANN index was not used" Key terms: explains, index, show, tidb, used, vector, warnings

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Technical Details
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Published by
issueatlas
Published
Skill ID
skl_Sr2enea0PH6th_jlHNhljg
Version ID
skv_1G4EPcP_B-L0U6sM9vphMQ
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More public guidance matched to this skill.

TiDB Vector Search: ANN index not used - EXPLAIN shows warningsTiDB Vector Search: ANN index not used - EXPLAIN shows warnings: : the two classic causes: ordering by the wrong distance function (the index is built on one function, for example cosine, and the query orders by L2), and using DESC order when the index only supports ascending.Read skill →SingleStore Vector: query not using the ANN index - EXPLAIN checkSingleStore Vector: query not using the ANN index - EXPLAIN check: : if INTERNAL_VECTOR_SEARCH is not in the ColumnStoreFilter line of EXPLAIN, the vector index is not being used.Read skill →SingleStore vector range search: EXPLAIN proves the index is usedSingleStore vector range search: EXPLAIN proves the index is used: : in the EXPLAIN output, the ColumnStoreFilter row shows INTERNAL_VECTOR_RANGE_SEARCH when the plan uses a vector index for range search.Read skill →

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Published recentlyPublished Oct 1, 2026. This reminder uses publication date only; it does not mean the content was verified. Review again after Mar 30, 2027.

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