An upload delta is the difference in data between one built version of a snap to the next. During an upload, Snapcraft sends that difference to the Snap Store. A delta saves bandwidth and disk space by patching only the necessary changes between snap versions. Upload deltas are enabled by default and are processed in the background during the development workflow.
When a snap developer uploads a new version of a snap, Snapcraft automatically generates a file containing only the changes from the most recently uploaded version to the new version and uploads it to the Snap Store. The store then applies the changes to form the same snap that would have been uploaded in its entirety, and verifies the contents with a digital signature.
It’s important to note that upload deltas are distinct from download deltas. Upload deltas don’t feed into download deltas.
Upload deltas are available in Snapcraft 2.28 and higher.
Suppress upload deltas
If needed, you can prevent upload deltas from being uploaded. Doing so can help in the unusual case where a snap has many channels and delta generation takes up a significant amount of the upload time, causing the delta service to time out.
To suppress upload deltas, prior to uploading a new snap version, delete your snap’s directory in ~/.cache/snapcraft/projects/. The delta for each channel then won’t generate for that upload.