154b2b2296 [fuzz] V3_MAX_VSIZE and effective ancestor/descendant size limits (glozow)
a29f1df289 [policy] restrict all v3 transactions to 10kvB (glozow)
d578e2e354 [policy] explicitly require non-v3 for CPFP carve out (glozow)
Pull request description:
Opening for discussion / conceptual review.
We like the idea of a smaller maximum transaction size because:
- It lowers potential replacement cost (i.e. harder to do Rule 3 pinning via gigantic transaction)
- They are easier to bin-pack in block template production
- They equate to a tighter memory limit in data structures that are bounded by a number of transactions (e.g. orphanage and vExtraTxnForCompact). For example, the current memory bounds for orphanage is 100KvB * 100 = 40MB, and guaranteeing 1 tx per peer would require reserving a pretty large space.
History for `MAX_STANDARD_TX_WEIGHT=100KvB` (copied from https://github.com/bitcoin/bitcoin/pull/29873#issuecomment-2115459510):
- 2010-09-13 In 3df62878c3 satoshi added a 100kB (MAX_BLOCK_SIZE_GEN/5 with MBS_GEN = MAX_BLOCK_SIZE/2) limit on new transactions in CreateTransaction()
- 2013-02-04 https://github.com/bitcoin/bitcoin/pull/2273 In gavin gave that constant a name, and made it apply to transaction relay as well
Lowering `MAX_STANDARD_TX_WEIGHT` for all txns is not being proposed, as there are existing apps/protocols that rely on large transactions. However, it's been brought up that we should consider this for TRUCs (which is especially designed to avoid Rule 3 pinning).
This reduction should be ok because using nVersion=3 isn't standard yet, so this wouldn't break somebody's existing use case. If we find that this is too small, we can always increase it later. Decreasing would be much more difficult.
~[Expected size of a commitment transaction](https://github.com/lightning/bolts/blob/master/03-transactions.md#expected-weight-of-the-commitment-transaction) is within (900 + 172 * 483 + 224) / 4 = 21050vB~ EDIT: this is incorrect, but perhaps not something that should affect how we choose this number.
ACKs for top commit:
sdaftuar:
ACK 154b2b2296
achow101:
ACK 154b2b2296
instagibbs:
ACK 154b2b2296
t-bast:
ACK 154b2b2296
murchandamus:
crACK 154b2b2296
Tree-SHA512: 89392a460908a8ea9f547d90e00f5181de0eaa9d2c4f2766140a91294ade3229b3d181833cad9afc93a0d0e8c4b96ee2f5aeda7c50ad7e6f3a8320b9e0c5ae97
