Quote from: KurtB on August 20, 2015, 01:30:24 PM

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Older blocks may no longer be considered valid blocks under new rules

- I can't believe that, older blocks are valid because they exist and have been confirmed everything else would contradict immutability.

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If the version numbers did not exist, then we would have an issue where some v2 blocks are no longer valid under v3 rules and the clients would get all screwed up because they have historic blocks that don't validate.

- The version number is a variable(!), every miner is free to choose whatever she wants. If what you say is true, somebody could create quite a mess with sending an old version number. In such a case we should remove it as bug urgently.

Quote from: knightdk on August 20, 2015, 03:22:34 AM

Version numbers also help to facilitate miner voting. Miners voted for using BIP66 rules by producing v3 blocks. BitcoinXT nodes vote for BitcoinXT by producing blocks with 0x20000007 set as the version.

- They can also facilitate forking, again, there are clearly different versions being developed right now.

Maybe, we have only a very narrow window open to make such changes to the block layout. Once there are 5 different implementations out there it will be impossible to even change such a small matter.

Clearly you have not read the documentation. Historical blocks of older version numbers are still valid and may be validated inner different rules. At a certain point old version numbers are considered invalid so blocks with older versions are not valid and discarded by the client.

Any version number that is not defined in the client will be validated as the current version which is why xt blocks can currently be accepted by Bitcoin core.

Quote from: KurtB on August 20, 2015, 01:38:04 PM

- How come? The header clearly not.
- Also, from what I read the transactions aren't either.
Thus, most of the volume is uncompressed.

However, you are right, compression would require more CPU cycles, but simple reductions could come at a very low cost of maybe 0.1% performance. Nothing in comparison to the saved bandwidth and HDD space.

The hashes cannot be losslessly compressed because hashes are random. I'd they are look say compressed them data is losses and hairs won't match.