Question

I am working on an app wherein users will create a data object and upload it to storage. They will then download it later, make some changes, and upload those changes (as a patch to the original data). Is there a way to use the blobstore or cloud storage to upload the patch and have it applied so that my users do not have to upload the whole data object again (which can grow quite large)?

Answer 1

You can’t issue incremental updates to data in Blobstore or Cloud Storage. To apply a patch, you will have to apply it yourself and overwrite the data in the blob or object. Relevant information is below.

From the Concepts and Terminology section of the Google Cloud Storage docs:

Objects are immutable, which means that an uploaded object cannot
change throughout its storage lifetime. An object’s storage lifetime
is the time between successful object creation (upload) and successful
object deletion. In practice, this means that you cannot make
incremental changes to objects, such as append operations or truncate
operations. However, it is possible to overwrite objects that are
stored in Google Cloud Storage because an overwrite operation is in
effect a delete object operation followed immediately by an upload
object operation. So a single overwrite operation simply marks the end
of one immutable object’s lifetime and the beginning of a new
immutable object’s lifetime.

From the Blobstore Introduction section:

Blobs can’t be modified after they’re created, though they can be
deleted. Each blob has a corresponding blob info record, stored in the
datastore, that provides details about the blob, such as its creation
time and content type. You can use the blob key to fetch blob info
records and query their properties.