f40ab83d02
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.
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Vector index in Scylla
Vector indexes are custom indexes (USING 'vector_index'). Their target option in system_schema.indexes uses following format:
- Simple single-column vector index
(v): just the (escaped) column name, e.g.v - Vector index with filtering columns
(v, f1, f2): JSON withtc(target column) andfc(filtering columns):{"tc":"v","fc":["f1","f2"]} - Local vector index
((p1, p2), v): JSON withtcandpk(partition key columns):{"tc":"v","pk":["p1","p2"]} - Local vector index with filtering columns
((p1, p2), v, f1, f2): JSON withtc,pk, andfc:{"tc":"v","pk":["p1","p2"],"fc":["f1","f2"]}
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.
Metadata semantics
Vector indexes also store an index_version option in system_schema.indexes.
It is an auto-generated timeuuid created by CREATE INDEX, and it identifies a specific index creation time.
In particular:
- dropping and recreating the same vector index definition generates a new
index_version; - altering the base table does not change an existing vector index's
index_version; - 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).
Duplicate detection
Scylla allows multiple named vector indexes on the same target column. This is useful for zero-downtime recreation: create a replacement index, let it build, and then drop the older one.
Unnamed duplicate vector indexes are still rejected. For identity detection, index_version is ignored,
because it changes on every CREATE INDEX even when the logical index definition stays the same.