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Document the new vector index behavior in the user-facing and developer docs. Describe `index_version` as a creation timeuuid stored in `system_schema.indexes`, clarify that recreating an index changes it while ALTER TABLE does not, and document that Scylla allows multiple named vector indexes on the same column while still rejecting unnamed duplicates.
30 lines
1.8 KiB
Markdown
30 lines
1.8 KiB
Markdown
# Vector index in Scylla
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Vector indexes are custom indexes (USING 'vector\_index'). Their `target` option in `system_schema.indexes` uses following format:
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- Simple single-column vector index `(v)`: just the (escaped) column name, e.g. `v`
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- Vector index with filtering columns `(v, f1, f2)`: JSON with `tc` (target column) and `fc` (filtering columns): `{"tc":"v","fc":["f1","f2"]}`
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- Local vector index `((p1, p2), v)`: JSON with `tc` and `pk` (partition key columns): `{"tc":"v","pk":["p1","p2"]}`
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- Local vector index with filtering columns `((p1, p2), v, f1, f2)`: JSON with `tc`, `pk`, and `fc`: `{"tc":"v","pk":["p1","p2"],"fc":["f1","f2"]}`
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The `target` option acts as the interface for the vector-store service, providing the metadata necessary to determine which columns are indexed and how they are structured.
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## Metadata semantics
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Vector indexes also store an `index_version` option in `system_schema.indexes`.
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It is an auto-generated timeuuid created by `CREATE INDEX`, and it identifies a specific index creation time.
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In particular:
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- dropping and recreating the same vector index definition generates a new `index_version`;
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- altering the base table does not change an existing vector index's `index_version`;
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- when multiple named vector indexes exist on the same target column, the Vector Store routes queries to the most recent, serving one (with the highest `index_version`).
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## Duplicate detection
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Scylla allows multiple **named** vector indexes on the same target column.
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This is useful for zero-downtime recreation: create a replacement index, let it build, and then drop the older one.
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Unnamed duplicate vector indexes are still rejected. For identity detection, `index_version` is ignored,
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because it changes on every `CREATE INDEX` even when the logical index definition stays the same.
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