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+From: Troy Benjegerdes <hozer@hozed.org>

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+Subject: Re: [bitcoin-dev] Height based vs block time based thresholds

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+

+On Tue, Jul 04, 2017 at 09:30:26PM -0400, shaolinfry via bitcoin-dev wrote:

+> Some people have criticized BIP9's blocktime based thresholds arguing they are confusing (the first retarget after threshold). It is also vulnerable to miners fiddling with timestamps in a way that could prevent or delay activation - for example by only advancing the block timestamp by 1 second you would never meet the threshold (although this would come a the penalty of hiking the difficulty dramatically).

+

+If there are miners that start doing 1 second timestamp advances, it would be

+simpler (and probably safer) to require a minimum block time spacing of say

+30 seconds or 1 minute, and orphan blocks that are too close in time and more

+than say an hour behind real-time.

+

+I cannot picture any realistic scenario in which an attempt to block activation

+in this way is in anything other than a very expensive temper tantrum for any

+miners foolish enough to attempt it.

+

+It *might* be a delay tactic as a 'nuclear option' attack vector for a mining

+cabal to run up the difficulty so high as to make it impractical to mine any

+new blocks after the adjustment, but there are plenty of altcoins that have

+hardforked and gotten along just fine after the same kind of thing due to

+profit-switching pools.

+

+

+> On the other hand, the exact date of a height based thresholds is hard to predict a long time in advance due to difficulty fluctuations. However, there is certainty at a given block height and it's easy to monitor.

+> If there is sufficient interest, I would be happy to amend BIP8 to be height based. I originally omitted height based thresholds in the interests of simplicity of review - but now that the proposal has been widely reviewed it would be a trivial amendment.

+

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+