Put the system metadata part ahead of the object part when d1_client_python constructs the multipart
When a client calls the mn.create/update methods, it usually constructs a multipart which contains the sys part (containing the system metadata information), object part (containing the object itself) and other parts. There is no requirement about the order of those parts.
Metacat will use a new streaming multipart handler which will calculate the checksum when it stores the object part into a file. This requires we should know the checksum algorithm before the serialization of the object. So Metacat has to digest the system metadata first in order to improve the performance.
In order to take the advantage, we recommend clients should put the system metadata part ahead of the object part when it is constructing the multipart to be sent to the server.
Note: event though the client doesn't use the recommended order, the process still works but the performance will be poor.