Re-checking and rechecking resume data blocking downloading and uploading

[roberth1990]

qBittorrent version and Operating System:

Version 3.3.16 and Windows 10

What is the problem:

When you are downloading and seeding a lot of large torrents(mostly from 17 to 35 gb) in my case 12 downloads, when one of the large downloads are being re-checked at once all other downloads gets stalled and no completed downloads are seeding, this happens for a while, maybe all the downloads starts downloading a few bytes per second, or a bit more for a few seconds and then they get stalled again. All the downloads and completed downloads are spread across different drives, so it's not an I/O or throughput performance issue on the drives. CPU usage remains low.
Exact same behavior occours when just re-checking resume data.

What is the expected behavior:

Downloading and uploading torrents should not be blocked or partially blocked when there is no hardware performance limitation.

Steps to reproduce:

Add a lot of large torrents(17-35 or even larger) when 12 of them are downloading, re-check one torrent and this behaviour appears.

[thalieht]

Duplicate #4408 #5649 #6657

[coolio2013]

qbt v3.4.0beta2 with libtorrent v1.1.5.0 can check several torrents, affecting seeding/leeching much less, if at all (compared to previous libtorrent v1.0.x, which could only check 1 torrent, blocking seeding/leeching completely at times on my system. It was so bad I even considered changing OS/FS with much better caching than Windows, i.e. TrueOS with ZFS). Also, the size of the payload does not seem to matter any more with qbt v3.4.0beta2.

Unfortunately there is no setting to limit the numbers of torrents allowed to be checked (for example via aio_threads, see arvidn/libtorrent#1980, and http://www.libtorrent.org/single-page-ref.html).

[wilson]

I am experiencing this on v3.3.16 (FreeBSD, ZFS) as well.

[petemmitchell]

I am currently experiencing this on v4.0.0 64 bit, Windows 10.

Was happening in my v3.x for the last few versions too. #7587 is the best description of what happens.

[sledgehammer999]

This issue has been closed and locked for being too old, and thus either most likely resolved in recent versions or no longer applicable.
If you experience the reported problem or similar in the latest version, please open a new issue report with the requested information in the issue template.

A new issue report with relevant updated data gathered from the latest version is preferable to necroing an old report with a comment like "still happens in version x.y.z", even if you think the bug is the same, or suspect of a regression.
Due to the changes made to the qBittorrent code and its dependencies over time, the exact cause of your problem could be totally different than the original one, despite the visible symptoms of the bug being similar.
Thus, providing relevant updated information is crucial to find and fix the root cause of a recurrent problem or regression.

Thank you for your contributions.