What is sequential downloading?

[sonumonu007]

I am a little confused by the sequential download feature. If I have a torrent which has multiple files, which file is it downloading sequentially? If I want to download a particular file sequentially out of many files in the torrent, how do i do that?

[KitKat]

Sequential downloading means to download all the torrent pieces in logical order.
Piece 1, piece 2, piece 3 and so on until the torrent completes.

It will download the first file in the torrent sequentially first, (file order is usually alphabetical but not always)

If you have a multifile torrent it will download each file one at a time in piece order. If you wish to download a specific file sequentially you have to tell qbittorent to "skip" all the other files in the torrent before it then tell it to download the skipped files again assuming you want them.

eg torrent contains files 1.mp4 2.mp4 and 3.mp4
I want to download 2.mp4 sequentially FIRST so i have to tell qbittorent to skip 1.mp4

/e:
The benefits of sequential downloading are streaming video files or obtaining fully complete files in multifile torrents more reliably.
Currently in version 3.3.3 the "streaming" aspect of sequential downloading is handicapped by a failure to download complete metadata in the (common) scenario when the metadata is located at the end of the file.
No metadata = file cannot play, and if its sequentially downloaded then you wont get the metadata til the file completely finishes making it pointless.

A PR that fixes this issue has been merged and this functionality is fixed in 3.4.0 beta/alpha and the next release (whenever that happens).

The Disadvantages of sequentual downloading are swarm related, more people sequentially downloading = more load on the seeders due to less unique content available for sharing.
(If 100 people want piece #300 and only 5 people have it then there is a big chokepoint for the people trying to get that piece).

Hope this explanation helped/answered your questions!

[ciaobaby]

It will download the first file in the torrent sequentially first, (file order is usually alphabetical but not always)

Not necessarily, and the default order for files in the payload is by size[/], largest first.

[postcd]

Is this type of downloading (sequential/streaming mode) decreasing chances to download same amount of data as with regular downloading mode?
I mean for example if some bittorrent clients does not support this mode, i may loose peers to download from or all BT clients supports this mode or BT client will failover to regular download mode in case peer does not support sequential?
I have not found any information about that at https://libtorrent.org/streaming.html

[bob2306]

It isn't a specific mode, it just a matter of the order in which your client requests pieces from other clients.

It can slow down the torrent overall and increase the risk of a torrent going incomplete if too many peers do it simultaneously.

[postcd]

It can ... increase the risk of a torrent going incomplete

Thanks, I think that this is only true for the time when the torrent is newly seeded, but when it is established with numerous people downloaded it, the risk should not be higher than with default mode of downloading torrent pieces.

[bob2306]

It can ... increase the risk of a torrent going incomplete

Thanks, I think that this is only true for the time when the torrent is newly seeded

That's not very likely, the risk is at the other end of the torrent's life when there are few seeds.