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From: Hector Chu <hectorchu@gmail.com>
Date: Wed, 19 Aug 2015 13:51:14 +0100
Message-ID: <CAAO2FKFz7kSzkB58aAqYPNe8kh8Oe0oVqxXweq9KhHKae4frpA@mail.gmail.com>
To: Jameson Lopp <jameson.lopp@gmail.com>
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Cc: Bitcoin Dev <bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] A solution to increase the incentive of running a
	node
Precedence: list

On 19 August 2015 at 13:44, Jameson Lopp <jameson.lopp@gmail.com> wrote:
> It's possible to check that a transaction is cryptographically valid without
> having any blockchain data available; are you referring to a different type
> of validation?

It seems laborious to enumerate all the validations that are performed
on a transaction before it can be mined into a block, but for starters
we need to check it isn't a double-spend, and that its signatures
satisfy the outputs' pubkeys.

> If you're running an SPV node that is listening to full nodes on the
> network, you can request an unconfirmed transaction from connected peers
> after receiving the inventory message they send - that's how unconfirmed
> transactions propagate through the node network. This is not 100% proof that
> the transaction is valid for inclusion in the blockchain, but it's a very
> good indicator.

If you as an SPV node are waiting for unconfirmed transactions to be
relayed to you, you are going to have a slow start in mining those
transactions, decreasing the likelihood of receiving the mining
reward. Nodes should accept the first POW for a transaction and
discard any subsequent ones received.