Constant LOGICAL_TABLE_METADATA_KEY 

pub const LOGICAL_TABLE_METADATA_KEY: &str = "on_physical_table";

Metadata key present in the CREATE TABLE ... WITH () clause. This key is used to identify a logical table and associate it with a corresponding physical table . E.g.:

CREATE TABLE logical_table (
    ...
)
ENGINE = metric
WITH (
    on_physical_table = "physical_table",
);

And this key will be translated to corresponding physical REGION id in metasrv.