Subject: Re: [Bitcoin-development] BIP 34: Block v2, Height in Coinbase

From: Gavin Andresen <[email-masked]>
Date: Fri, 6 Jul 2012 16:02:16 -0400

> But those issues are solvable through other, non-backwards incompatible
> means. For example, mandate that a <transaction hash, output index> refers
> to the first such pair that is not already spent. No?

Yes, that is essentially what BIP 30 did.

We want to do this also, partly for "belt and suspenders" security but
mostly for two reasons:

1. To test using block/transaction version numbers to smoothly roll
out changes. The next change we need to make might be prompted by some
crisis; better to learn any lessons now, when we have the luxury of
time to fix problems that might crop up.

2. We think we'll all appreciate the change in a year or three, when
the whole network has upgraded and we can start writing code that
assumes all new blocks past a certain checkpoint contain their height;
that should make it easier to do things like figure out whether or not
an orphan chain can possibly be part of the main chain.

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Gavin Andresen