For anyone who missed the discussions of weak blocks, here are the Scaling
Bitcoin's transcripts:

http://diyhpl.us/wiki/transcripts/scalingbitcoin/bitcoin-block-propagation-iblt-rusty-russell/

http://diyhpl.us/wiki/transcripts/scalingbitcoin/roundgroup-roundup-1/
(under Network Propagation).

On Wed, Sep 23, 2015 at 4:43 PM, Gavin Andresen via bitcoin-dev <
bitcoin-dev@lists.linuxfoundation.org> wrote:

> I've been thinking about 'weak blocks' and SPV mining, and it seems to me
> weak blocks will make things better, not worse, if we improve the mining
> code a little bit.
>
> First:  the idea of 'weak blocks' (hat tip to Rusty for the term) is for
> miners to pre-announce blocks that they're working on, before they've
> solved the proof-of-work puzzle. To prevent DoS attacks, assume that some
> amount of proof-of-work is done (hence the term 'weak block') to rate-limit
> how many 'weak block' messages are relayed across the network.
>
>
> Today, miners are incentivized to start mining an empty block as soon as
> they see a block with valid proof-of-work, because they want to spend as
> little time as possible mining a not-best chain.
>
> Imagine miners always pre-announce the blocks they're working on to their
> peers, and peers validate those 'weak blocks' as quickly as they are able.
>
> Because weak blocks are pre-validated, when a full-difficulty block based
> on a previously announced weak block is found, block propagation should be
> insanely fast-- basically, as fast as a single packet can be relayed across
> the network the whole network could be mining on the new block.
>
> I don't see any barrier to making accepting the full-difficulty block and
> CreateNewBlock() insanely fast, and if those operations take just a
> microsecond or three, miners will have an incentive to create blocks with
> fee-paying transactions that weren't in the last block, rather than mining
> empty blocks.
>
> .................
>
> A miner could try to avoid validation work by just taking a weak block
> announced by somebody else, replacing the coinbase and re-computing the
> merkle root, and then mining. They will be at a slight disadvantage to
> fully validating miners, though, because they WOULD have to mine empty
> blocks between the time a full block is found and a fully-validating miner
> announced their next weak block.
>
> .................
>
> Weak block announcements are great for the network; they give transaction
> creators a pretty good idea of whether or not their transactions are likely
> to be confirmed in the next block. And if we're smart about implementing
> them, they shouldn't increase bandwidth or CPU usage significantly, because
> all the weak blocks at a given point in time are likely to contain the same
> transactions.
>
> --
> --
> Gavin Andresen
>
>
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