presto-main/src/main/java/io/prestosql/connector/system/SystemTablesMetadata.java/SystemTablesMetadata/listSchemaNames
class SystemTablesMetadata:    @Override
    public List<String> listSchemaNames(ConnectorSession session)
    {
        return tables.listSystemTables(session).stream()
                .map(table -> table.getTableMetadata().getTable().getSchemaName())
                .distinct()
                .collect(toImmutableList());
    }