LastModified (last modified time) is an important attribute of OSS objects. It is used in billing, incremental migration, and lifecycle rules. When you perform some operations on objects, the LastModified values of the objects are updated. The following table lists the common operations on objects.

Common operation API operation Whether the LastModified value of the object is updated
Modify object ACLs CopyObject Yes
PutObjectACL Yes
Modify the user metadata of an object CopyObject Yes
Modify the storage class of an object CopyObject Yes
CommitTransition No
Modify the encryption algorithm for an object CopyObject Yes
Overwrite an object PutObject Yes
CopyObject Yes
Add or modify object tags PutObjectTagging No
Delete an object tag DeleteObjectTagging No
Restore an Archive or Cold Archive object RestoreObject No
  • When you modify the storage class of an object by using the OSS console, ossutil, ossbrowser, or SDKs, OSS generates a new object of the specified storage class to overwrite the original object.
  • The last modified time of an object is updated when the object is overwritten or the storage class and encryption method are changed by using CopyObject. If the object whose last modified time is updated is an IA, Archive, or Cold Archive object and is stored for a period less than the minimum storage duration, you are charged for the minimum storage duration. For more information, see Storage fees.

    For example, if you change the storage class of an object from IA to Archive by using the OSS console after the object is stored for 12 days, the last modified time of the object is updated. In addition, you are charged for the minimum storage duration of an IA object, which is 30 days.