Feature Request

As I see you are already using \WP_Stream\DB_Driver_WPDB, which can be be made pluggable.

ref: https://github.com/xwp/stream/blob/3.9.1/classes/class-db-driver-wpdb.php#L13

So for starters, something like this:

before:

public function __construct() {
...
		global $wpdb;
		$prefix = apply_filters( 'wp_stream_db_tables_prefix', $wpdb->base_prefix );
...
}

after:

public function __construct() {
...
		global $wpdb;
		
		$custom_$wpdb = apply_filters( 'wp_stream_db_tables', $wpdb );
		$prefix = apply_filters( 'wp_stream_db_tables_prefix', $custom_$wpdb->base_prefix );
...
}

ref: https://github.com/xwp/stream/blob/3.9.1/classes/class-db-driver-wpdb.php#L41

So where ever $wpdb is referenced, we could replace it if needed.

Reason

We have about 15 million entries for Stream, which is not ideal, slows down our website significantly, so would like it to be offloaded, so it can store / retrieve data from secondary database.