Swarm Merging

The swarm merging feature allows you to download the same file using multiple torrents. This gives you two important benefits:

1. It typically results in faster downloads.
2. When one torrent is incomplete and has no seeds, you can finish the file with the second torrent, and be the hero that provides the final pieces to the swarm with the incomplete torrent. BiglyBT will also prioritize pieces that are missing from either swarm for faster healing.

UI

• Swarm Merge Column. This displays the number of bytes you've merged from the other torrent. The tooltip will list the files it is merging.
• You will receive notifications in the bottom right corner of BiglyBT when a file is successfully merged or when a merge has failed. (Merge failures are harmless and the reporting is merely informational.)

Settings

Configuration is visible in Advanced mode in Tools->Options->Files. Three options govern Swarm Merging:

1. "Attempt to merge incomplete files that are the same size" enables/disables Swarm Merging (default is on).
   1. "Try to complete all copies of the file..." controls whether BiglyBT attempts to complete all torrents with the same file, instead of just one (default is just one). Enabling this option lets you seed an incomplete torrent swarm from a completed torrent. See History below.
   2. "Size tolerance for identical file names (bytes)" sets the tolerance for matching possible merge candidates (default is 0 bytes, files must be exactly the same size).

Caveats

1. You will end up having multiple copies of the same file.
2. Merge candidate matching is based only on file size (within the tolerance described above, if the names are also identical). This could result in false matches. If merge candidates do not have the same contents, Swarm Merging will fail to merge the files and report the failure. (Each file will be completed separately from its own swarm, in the normal manner.)

Finding Torrents with the Same File

1. With Swarm Discoveries, you can open the context menu on a file you wish to find duplicates of, and choose "Swarm Discoveries: File Size"
2. Per torrent chat will display messages when other users in the swarm have found matching files.

History

The initial aim of the feature was the scenario where you've almost completed a download but some last file(s) don't have 100% availability in the swarm. So you go looking for another download that contains the missing files, add it to BiglyBT and wait for the original download to complete. You then stop and remove the second download. In this case it isn't necessary to consider completed downloads for swam merging.

Then people wanted to deliberately ressurect dead downloads. The "Attempt to merge incomplete files that are the same size" option was added to allow data from a complete download to be merged into an incomplete one.

Enabling the option requires BiglyBT to use more resources if you have lots of complete downloads as these are considered in the merging process.