redis/redis-py · error · ValueError

Given database is not a member of database list

Error message

Given database is not a member of database list

What it means

Raised as ValueError by MultiDBClient.set_active_database() (client.py:151) when the supplied Database object is not found in self._databases. Promotion to active requires the database to already be a registered member of the client's weighted database list; an unknown object is rejected before any health check runs.

Source

Thrown at redis/multidb/client.py:151

    def get_databases(self) -> Databases:
        """
        Returns a sorted (by weight) list of all databases.
        """
        return self._databases

    def set_active_database(self, database: SyncDatabase) -> None:
        """
        Promote one of the existing databases to become an active.
        """
        exists = None

        for existing_db, _ in self._databases:
            if existing_db == database:
                exists = True
                break

        if not exists:
            raise ValueError("Given database is not a member of database list")

        self._bg_scheduler.run_coro_sync(self._check_db_health, database)

        if database.circuit.state == CBState.CLOSED:
            highest_weighted_db, _ = self._databases.get_top_n(1)[0]
            self.command_executor.active_database = (
                database,
                GeoFailoverReason.MANUAL,
            )
            return

        raise NoValidDatabaseException(
            "Cannot set active database, database is unhealthy"
        )

    def add_database(
        self, config: DatabaseConfig, skip_initial_health_check: bool = True
    ):

View on GitHub (pinned to 6a6b581b48)

Solutions

  1. Only pass Database instances returned by client.get_databases() to set_active_database().
  2. If the target isn't registered, add it first via client.add_database(config).
  3. Resolve the desired database from get_databases() by matching its identity field rather than reconstructing it.

Example fix

# before
new_db = Database(client=other_client, circuit=..., weight=1)
client.set_active_database(new_db)  # raises ValueError

# after
client.add_database(db_config)            # register it first
target = next(db for db, _ in client.get_databases() if db is desired)
client.set_active_database(target)
Defensive patterns

Strategy: validation

Validate before calling

# Validate membership before promoting
registered = [db for db, _ in client.get_databases()]
if database not in registered:
    raise ValueError('database is not registered with this client')
client.set_active_database(database)

Type guard

from redis.multidb.client import MultiDBClient

def is_registered(client: MultiDBClient, database) -> bool:
    return any(db is database for db, _ in client.get_databases())

Try / catch

try:
    client.set_active_database(database)
except ValueError as e:
    if 'not a member' in str(e):
        # register first, then promote
        client.add_database(config_for(database))
        client.set_active_database(database)
    else:
        raise

Prevention

When it happens

Trigger: Passing a freshly constructed Database (not added via add_database()) to set_active_database(); passing a Database belonging to a different MultiDBClient instance; passing an object that fails equality against the registered entries (Database.__eq__ compares underlying fields).

Common situations: Calling set_active_database with a Database reference obtained outside the client; swapping client instances and reusing old Database handles; mutating fields that affect equality after registration.

Related errors

AI-assisted analysis of redis/redis-py@6a6b581b48 (2026-08-10). Data as JSON: /api/errors/5cddfc776aeb26db. Report an issue: GitHub.