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Date: Thu, 5 Sep 2013 13:58:52 +0400
From: Solar Designer <solar@...nwall.com>
To: john-dev@...ts.openwall.com
Subject: Re: Parallella: Litecoin mining

Rafael,

On Thu, Sep 05, 2013 at 05:08:11AM +0100, Rafael Waldo Delgado Doblas wrote:
> I mean that if there is a block found on the network, the miner stops
> working on old data and begins to hash the next block. I'm getting a lot of
> longpolls then is it possible that cgminer never finds a share because
> doesn't mine fast enough?.

This is a good point.  However, please note that with mining many things
are probabilistic.  The time it'd take for us to find a share will vary.
Although it might take e.g. 2 hours on average at the awful speed we
currently have, it might also take e.g. 1 second if we're really lucky.
My understanding is that when we're forced to start mining for a new
block, we lose only a very small portion of work (and actually some
pools accept "stale shares", I think).  On one hand, yes, our "2-hour
average" (or whatever) period starts anew, but on the other it does not
matter for our chances to find a share on any given second.

Here's an analogy: computer hardware MTBF:
http://en.wikipedia.org/wiki/Mean_time_between_failures
For example, a hard disk drive might have an MTBF of 1000000 hours.
If we replace HDDs every hour, will we never encounter a HDD failure?
Per the MTBF model, no - we'll run into a HDD failure anyway, as long as
the density function is not a constant zero for the 0 to 1 hour period.
Often it is assumed to be such that we'd run into failures every
1000000 hours on average anyway.  And it is actually (almost) such in
cryptocurrency mining, I think.

Alexander

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