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.
Queries against local vector indexes were failing with the error:
"ANN ordering by vector requires the column to be indexed using 'vector_index'"
This was a regression introduced by 15788c3734, which incorrectly
assumed the first column in the targets list is always the vector column.
For local vector indexes, the first column is the partition key, causing
the failure.
Previously, serialization logic for the target index option was shared
between vector and secondary indexes. This is no longer viable due to
the introduction of local vector indexes and vector indexes with filtering
columns, which have different target format.
This commit introduces a dedicated JSON-based serialization format for
vector index targets, identifying the target column (tc), filtering
columns (fc), and partition key columns (pk). This ensures unambiguous
serialization and deserialization for all vector index types.
This change is backward compatible for regular vector indexes. However,
it breaks compatibility for local vector indexes and vector indexes with
filtering columns created in version 2026.1.0. To mitigate this, usage
of these specific index types will be blocked in the 2026.1.0 release
by failing ANN queries against them in vector-store service.
Fixes: SCYLLADB-895
