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"Wasted" missing documentation and high proportion #10354

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ke352802081770314 opened this Issue Mar 7, 2019 · 0 comments

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ke352802081770314 commented Mar 7, 2019

Please provide the following information

qBittorrent version and Operating System

4.1.0
Ubuntu 18.04.2 LTS

If on linux, libtorrent and Qt version (from About/Libraries)

Qt 5.9.1
Libtorrent 1.1.7.0
Boost 1.62.0

What is the problem

In a torrent I am downloading,
104.0MB downloaded 14.8MB wasted (which means only 89.2MiB usable of 104MiB, 16.6% overhead based on usable)
Help/Documentation opens a Browser window doc.qbittorrent.org, redirecting to https://github.com/qbittorrent/qBittorrent/wiki but in this wiki, user documentation is drowned by developer dolcumentation, making it hard for normal users to find information, and I found neither an explanation of "Wasted" nor hints how to optimize it.

I was able to reduce the waste ratio by reducing the maximum number of connections per torrent, and it may also help to reduce the per-torrent bandwidth to 8KiB/s, but I still get 2-8% wasted, and the waste starts early on during the download.

What is the expected behavior

of qBT: not to waste bandwidth, even more so when the connection is very slow as this means every MiB wasted extends the download time and is painful. How: see below
of doc.qbittorrent.org: to provide or redirect to user documentation, clearly offset from developer documentation

In https://qbforums.shiki.hu/index.php/topic,4565.msg23362.html#msg23362 I found a statement that qBT tries to re-download the same piece from a hopefully faster seed/peer.
I think as long as there are more remaining pieces than connected seeds/peers, qBT should prioritize assigning a separate piece to each connection and only start to request overlapping parts of the same piece from different peers if no fresh piece can be requested from a peer any more. It is better to have as many partial pieces as peers than to waste bandwidth.

Steps to reproduce

Be on a slow connection, e.g. mobile "volume exceeded" reduced bandwidth (here, 64kbps) or use some other traffic shaper to limit the bandwidth provided by the network to very little. Set maximum connections per torrent to 30 (really bad results) or 10 (more moderate results but still significant waste). Download a well-seeded torrent of say 100MiB size with 256KiB pieces (which would give plenty of pieces to distribute between the connected seeds/peers). Be patient as download time is expected to be around 6 hours and observe "wasted" metric.

Extra info(if any)

none

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