user20920: If the bitcoin protocol were changed so that the merkle root from block N-1 were replaced in block N by the two roots of blocks N-2 and N-3, then it would become possible to mine 2 blocks at a time in parallel and increase the block frequency compared to the time each block took to propagate. Each block would still get confirmed by 6 of the following 7 blocks. The block size variance could be controlled by requiring that transactions with odd hashes go into odd-numbered blocks and vice-versa. What would be the limitations of this variant protocol compared to the existing Bitcoin protocol, assuming nobody considered one confirmation to be much better than zero?

user5292: Objections that come to mind initially, I'm sure there are more:

You don't want to split the hashing power into two halves because that would make it easier for an adversary to get 51% of that halve: 25% of the total or even less if the halves are not exactly 50-50.
The idea behind Proof of Work is to concentrate as much work as possible behind one and the same chain and make that the level-to-beat by an attacker.

If you force odd transactions into odd blocks (and vice versa) then you still have 10 minutes block times for all transactions.



20920: <p>If the bitcoin protocol were changed so that the merkle root from block N-1 were replaced in block N by the two roots of blocks N-2 and N-3, then it would become possible to mine 2 blocks at a time in parallel and increase the block frequency compared to the time each block took to propagate. Each block would still get confirmed by 6 of the following 7 blocks. The block size variance could be controlled by requiring that transactions with odd hashes go into odd-numbered blocks and vice-versa. What would be the limitations of this variant protocol compared to the existing Bitcoin protocol, assuming nobody considered one confirmation to be much better than zero?</p>
 5292: <p>Objections that come to mind initially, I'm sure there are more:</p>
<ol>
<li><p>You don't want to split the hashing power into two halves because that would make it easier for an adversary to get 51% of that halve: 25% of the total or even less if the halves are not exactly 50-50.</p>
<p>The idea behind Proof of Work is to concentrate as much work as possible behind one and the same chain and make that the level-to-beat by an attacker.</p>
</li>
<li><p>If you force odd transactions into odd blocks (and vice versa) then you still have 10 minutes block times for all transactions.</p>
</li>
</ol>
