DeltaSync

Delta Sync

There is expiremental support for "Delta Sync" in ownCloud Desktop Client 2.6.0. Delta sync means that for some cases uploads and downloads don't need to transfer the complete file. Instead, if the new file is sufficiently similar to the old file, only the file changes are transfered.

Requirements

• ownCloud Desktop Client 2.6.0 or later
• ownCloud Server version >= 11
• In the desktop client, general settings, experimental section, enable the "Delta-Synchronization" feature.

If no delta sync is happening but you think the requirments are met, look for "[zsync disabled]" in the log file.

Limitations

Delta sync can only work if chunk metadata is available for the file in question. The client needs it to be able to determine what data can be reused. Each upload with a delta sync enabled client will also upload metadata for that file to the server. Currently that is the only way to populate the server's delta sync metadata.

Delta sync is limited to recognizing reusable 1 MiB chunks of the previous version of the file.

For uploads, the data to reuse most not have changed offset in the file. That means appending a byte or changing a byte will lead to a <= 1MiB transfer, but inserting a byte at the start will require the full file to be reuploaded.

Furthermore, delta sync only looks for reusable data from the previous version of the file. It cannot currently reuse data from other files even if they are identical.