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How does bt.prio_rare_thres work?


daftasbrush

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Just upgraded to 1500.. and I think I've got a problem with the "prioritizing rare pieces"

In about 30s uT has started D/Ling like 50 x 4Mb Pieces simultaneously.....

At this rate I'm going to have most of the torrent, before I complete more than a couple of pieces....

I suspect it's to do with the rare piece priority... but what does the setting do?

If it was True / False (like first/ last piece) I could turn it off...

But I've got 50? What's that mean?

What's Off (0?)

What's the number do? FAQ doesn't say... so far as I can see.

I suspect it's a test on the Availality of the piece... Is that right?

But that's going to be a problem when number of seeds and/or peers is low....

What if I only connect to 50 clients per torrent?

If the default is "Prioritize if Availablity < 50" then surely it's going to prioritize starting EVERY Piece in a new / low availability torrent...

Which seems to be what's happened to me.

Don't get me wrong, I think prioritizing rare pieces is a great idea... but it needs to be done right.

Better if it was a Percentage... (Actual Availability) / (Number of Connected Clients)

So that if less than N% of the current swarm have a piece, then it's rare... rather than less than N clients.

Or maybe change it to "On / Off" but only prioritize pieces at the lowest availablity...

So If Torrent "Availability" is 25.999 only prioritize start on pieces with 25 (and maybe 26) Availablity.

Or keep it as a number, but have that number be "above minimum availability"...

So if Torrent "Availability" is 25.999 and bt.prio_rare_thres is 5... you priortize starting pieces with Availability 25-30

or... the best way I've thought of... Prioritize Starting the Rarest N pieces...

So you effectively have N "piece slots" for the rarest pieces... You start them in turn "rarest" first... but once you've started N you switch back to normal, and only start another "rare" piece when one of the existing ones completes.

Anyway... A little more info on what the setting does,would be appreciated.

Cheers

Dan

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Yeah its 437... it popped-up and D/L'ed a couple of hours ago....

So what does bt.prio_rare_thres do then?

With it set to 0, I get about 10-15 pieces D/Ling..so that's "OK".. 'cos my D/L speed is maxed. Nice :)

but if I set it back to 50 (the default).. uT goes "mental" and starts loads more pieces... (like 50)

So now each piece is taking approx 5 times longer to complete... so I'm not sharing efficiently at all... because I've got around 50% of 50 pieces... when I could have 25 complete and be sharing them.

uT is starting about 1 piece every 20s, but now there's so many of them... one only completes every couple of minutes...

It will stop soon...

because it won't be long before it's simultaneously requesting EVERY piece in the torrent.... NOT GOOD.

I'll turn it back to 0... but I'm thinking your going to get a lot more of these posts... if the default is 50.

Plus I still don't know what it does... but zero seems to keep it "sane".

Cheers

Dan

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The point was so that it would open up the rarest pieces in the swarm (as well as common ones), and try to get them whenever available, thus making a full copy of the torrent come out faster. Since you don't want to take up all the "slots" with rare pieces, it has a lot more pieces in progress at once, so as to not kill yourself with only rare (slow) pieces.

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The point was so that it would open up the rarest pieces in the swarm (as well as common ones), and try to get them whenever available, thus making a full copy of the torrent come out faster. Since you don't want to take up all the "slots" with rare pieces, it has a lot more pieces in progress at once, so as to not kill yourself with only rare (slow) pieces.

So is the setting the Number of Rare Pieces to start

or

A "threshold" of rarity... and it starts (incrementally) any piece rarer than the setting.

or

Something else....

Whatever the answer... it might be worth putting it in the FAQ.

'cos 50's killing me.

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  • 2 months later...

Imo its a bad idea having an absolute number, how about having some percentage of all connected peers instead. 50 sources can be quite a lot on many torrents, but yet hardly anthing on others. It's also highly dependant on how many connections you accept globally and per torrent (I frequently see >300 peers with my personal settings).

That said I have set this to 0, as I feel it's better for both the swarm (less outstanding data before I can seed the piece back) and me (subjectively less memory usage and disc access).

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That makes sense, if the new behaviour is balanced. Between 0 and 1000 I've seen 5 times as many open pieces. I also hope it takes the chuck size into account (atleast a bit). I wouldn't mind having 100 active pieces at 256kb chunks, while the same 100 pices at 4Mb chunks would be quite a waste.

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