Chunk 2 gave search a configured set to fan out over. ask and analyze
covered one database still: the RAG capability had no way to be told which
databases a question spanned, and the analysis sandbox mounted one
document tree.
The selection travels as sources on EvidenceState, beside the filter it
scopes with, so both capabilities read it the same way. clients_covering
is the one rule that turns a selection into clients, used by search, the
sandbox mount and the cite fallback, so a question scoped to some
databases cannot search, mount or cite another. Citations carry the
database they came from, and format_for_agent names it, so the model can
attribute evidence while it answers rather than only afterwards.
The sandbox keeps one flat /documents/{id}/ namespace and resolves each id
to the client holding it, which rests on ids being UUID4. A database
copied from another breaks that, so an id held twice is refused rather
than resolved to whichever arrived last.
On the CLI, search, ask and analyze cover the configured set and label
each result with its database. Every other command works on one, named
with --database NAME (a name reaches a database behind a URI, which --db
cannot) or --db PATH, and refuses a set it cannot choose from instead of
silently reading the default database. Cold databases open together, so a
first query costs the slowest open rather than their sum.
`lancedb.databases` maps a name to a location, mutually exclusive with `uri`.
`search(sources=[…])` selects which to search, `sources=None` searches all of them
and `sources=[]` searches none; `SearchResult.source` carries the configured name,
so a path or URI never leaves the configuration. A database named in config keeps
its name even when it is the only one configured; only a legacy single `uri`
leaves `source` unset.
Databases open on first use, not at entry. Which are searched is a per-query
choice, so a set of 25 queried a few at a time opens a few, and a database nobody
asked for can neither fail a query nor be opened for nothing.
A named database that fails to open raises `SourceUnavailableError` naming it,
raised outside the handler so the original is not attached at all. A local failure
spells out the absolute path and an object-store failure can carry the bucket;
`from None` would only stop that being printed, leaving it on `__context__` for
anything that walks the chain. A legacy `uri` client has no name to report
instead, so its error passes through unchanged.
Candidates are fetched concurrently, then fused before anything is ranked. A
configured reranker scores the union, which is what makes ranking across
databases tractable: it compares query against document and does not care where a
candidate came from. Without one, reciprocal rank fusion over the per-database
rankings, since scores from separate indexes are not comparable. Enrichment then
runs on the survivors through the database each came from, concurrently, so it
costs what a single-database search costs.
The over-fetch decision and the reranker belong to the federating client alone.
Deciding per database would have each consult its own, and a local reranker loads
model weights per instance. It is built only for a text query, and closed once by
the client that owns it.
A location without a scheme is opened as a local path rather than through
`lancedb.uri`. Routing it through `uri` had `ConnectionMode` classify it as object
storage, which opens a missing database instead of reporting it.
With several databases configured, `store` and the repositories are left unset:
they have no unambiguous meaning across a set, and picking one silently would be
worse than the error.
