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Date: Mon, 1 Apr 2024 13:25:47 +0000
From: Andrew Poelstra <apoelstra@wpsoftware.net>
To: Jameson Lopp <jameson.lopp@gmail.com>
Cc: bitcoindev@googlegroups.com
Subject: Re: [bitcoindev] The Future of Bitcoin Testnet
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On Sun, Mar 31, 2024 at 09:19:50AM -0400, Jameson Lopp wrote:
> 
> 2. The reason the block height is insanely high is due to a rather amusing
> edge case bug that causes the difficulty to regularly get reset to 1, which
> causes a bit of havoc. If you want a deep dive into the quirk:
> https://blog.lopp.net/the-block-storms-of-bitcoins-testnet/
>

The purpose of this is to avoid situations where a single miner drives
the difficulty way up and then drops off, leaving the other testnet
miners unable to produce blocks. In the early CPU->GPU->FPGA->ASIC days
it could happen that there was only one person with an ASIC who would
have literally a 1000x advantage over other miners (since miner costs
money and nobody gets paid).

Nowadays we can probably assume that anyone who cares to mine testnet
can scrounge up a couple used S9s or something, so for a griefer to
obtain a 1000x advantage like this would require a serious cash
investment. So maybe it's okay to drop the rule entirely.

But I would propose weakening it -- requiring no blocks for a longer
period of time and resetting the difficulty to something (much) higher
than 1. Or just dropping the difficulty by a fixed factor of 128 or
something (though we'd need extra logic to avoid this being done
repeatedly to drive the difficulty to 1 anyway, maybe) so we don't
need to guess at a reasonable floor.

Obviously this is a major bikeshedding vector but hopefully people don't
get too enthusiastic about particular values here. Just pick something
and run with it.

Anyway ACK resetting testnet if people are valuing its coins. I recall
a long time ago this was (in some sense I don't remember) an official
condition under which testnet was supposed to be reset.


-- 
Andrew Poelstra
Director of Research, Blockstream
Email: apoelstra at wpsoftware.net
Web:   https://www.wpsoftware.net/andrew

The sun is always shining in space
    -Justin Lewis-Webster

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