[Feature Request] prioritize first and last piece

[didito]

hello,

i checked the forum, documentation and issues tracker - i did not find any info on this topic, so i thought i should ask.

would it be possible to have transmission prioritize the first and last pieces of each file.
to get a good chance and check the header of binary files before i have dowloaded megabytes ...
i can remember back in my windows days (now on mac and lovin transmission) when i used utorrent there was an option for that.

from the utorrent help file / documentation

bt.prio_first_last_piece: Enabling this option prioritizes the first and last pieces of each file in a torrent job, increasing the chances that they can be previewed before download completion. µTorrent will prioritize at least the first and last 1 MiB of data in a file.

this would help with previewing and identifying/authentificating video, audio and image files a lot, i guess...

anyway, just a thought. keep up the good work!

[jch]

would it be possible to have transmission prioritize the first and last pieces of each file.

Transmission does this by default. There is no need to set a preference.

--jch

[didito]

aha, that is interesting...
why is then, that movie files are more often broken until the full download is accomplished?
compared to utorrent, i mean. also when i take a look at the data pieces in the inspector it also seems to put less priority on continous data.
but to be honest i don't have accurate knowledge of header structures of the different movie formats.
i just have the (very subjective) impression that it works better with utorrent ...

[jch]

i just have the (very subjective) impression that it works better with utorrent

Thanks for the helpful bug report.

--jch

[Jordan]

aha, that is interesting...
why is then, that movie files are more often broken until the full download is accomplished?
compared to utorrent, i mean. also when i take a look at the data pieces in the inspector it also seems to put less priority on continous data.
but to be honest i don't have accurate knowledge of header structures of the different movie formats.
i just have the (very subjective) impression that it works better with utorrent ...

Hi didito,

Putting priority on continuous data is a different topic. I think it's correct to say that uTorrent does that more than Transmission does -- all other things being equal, Transmission uses a rarest-piece-first strategy in determining what data to go after next. It doesn't make any attempt to download sequentially.

This has been a long term question in the BitTorrent community. The active question is how harmful sequential downloading is to general swarm health, and whether it's acceptable for clients to do sequential downloading. At one point, it was a banworthy offense on some trackers. Now, sequental downloading seems to be a considered a desirable feature.

I think the jury is still out on the question. For now I want to play it safe wrt general swarm health, and see what effect sequential downloading by other clients has on the swarm.

[didito]

thanks for your interesting answer. i didn't know (read anticipate) that this really affects swarm health.
of course we don't want that. but since there seems to be an ongoing discussion about this, let's just keep that in our minds somewhere in the back ...
besides that, keep up the good work and thanks again for your time!

[Nicu]

Transmission uses a rarest-piece-first strategy in determining what data to go after next.

Overall, this sounds like a great strategy to me. But in the case of large files, the first parts make up for a small percent of the total download. It's quite valuable to be able to get the beginning and end of files like archives and ISO files, because they have the metadata there. For instance, 7-zip files have both start and end headers storing metadata, despite other formats only having it at the beginning of the file.

I think being able to prioritize the first and last pieces of large files, even individually, would be very useful for the more tech savvy people.

[killemov]

For 4.1 a sequentialDownload feature is added.