Quote from: zylstra on February 02, 2018, 08:46:55 AM

My question was because I read this:

Quote from: Jimmy_Song

When serialized to a Legacy node, they will be 400 bytes, 300 bytes and 500 bytes respectively (tx size without witness data). When serialized to a Segwit node, they will be 800 bytes, 1100 bytes and 500 bytes respectively.

That comment is talking about "Legacy Nodes" not "Legacy Blocks".

Where did you come up with the concept of a Legacy Block? the only Legacy Blocks are the blocks that were created before SegWit was activated. Or are you talking about SegWit blocks stored by a Legacy Node?

Quote from: zylstra on February 02, 2018, 08:46:55 AM

Quote from: Xynerise on February 02, 2018, 07:33:04 AM

If the witness data isn't included in segwit transactions then how do you validate a transaction without the signature? Huh

The same way you validate that same transaction when it's included in legacy blocks?

In Legacy Blocks the witness data is still there. It just isn't Segregated yet.

If you are asking about SegWit blocks stored by a Legacy Node, then those nodes are fooled into thinking that bitcoins sent to a SegWit address are sent to a "ANYONE CAN SPEND" output. Therefore, when they try to validate the blocks that spend those bitcoins, they are unable to tell the difference between a block where those bitcoins are validly spent or a block where they are invalidly spent. In other words, a Legacy Node is unable to fully validate a block that has transactions spending bitcoins that were previously received at a SegWit address. Instead, it must trust that those blocks have been validated by a SegWit node.

Quote from: zylstra on February 02, 2018, 08:46:55 AM

Or do legacy blocks need not validate segwit transactions? If not, why not?

There were no SegWit transactions yet back when Legacy Blocks were being created, therefore there was no need to validate them. (You can't validate something that doesn't exist).

If you are asking about SegWit blocks stored by a Legacy Node, then I've already explained that the Legacy Node can't tell the difference between a valid transaction that spends bitcoins which were previously received at a SegWit address and an invalid transaction that spends bitcoins which were previously received at a SegWit address. The Legacy Node must trust that the block has already been validated by a SegWit node.

Quote from: zylstra on February 02, 2018, 08:46:55 AM

As soon as we discovered we don't need witness data in legacy blocks why not simply cut them out?

It was never discovered that we don't need witness data.

Quote from: zylstra on February 02, 2018, 08:46:55 AM

So we agree that, on average, the block size will increase approximately 2x in Segwit. With that 2x size increase we will also get 2x throughput?

Yes.

Quote from: zylstra on February 02, 2018, 08:46:55 AM

If so, we could have done just as well simply increasing block size without Segwit.

Except that we would miss out on all the benefits that SegWit provides. SegWit was not intended to be a method of significantly increasing throughput. It was intended to fix some issues with bitcoin transactions (such as maleability), and to make other transaction types easier or possible.