Package Relay Project Tracking

This issue will be edited frequently to reflect the current status of the project.

What is ready for review now?

👇 👇 👇 #31829 ☝️ ☝️ ☝️

Tasks and PRs

☑️ (1) multi-parent-1-child package validation

What we get: the ability to validate multiple transactions, including CPFP of transactions below the mempool minimum feerate. An RPC to submit things locally.

See PRs

Enable validation of multiple transactions in MemPoolAccept
- Dependency: #21062
- Dependency: #23381
- Main feature 1/2: #20833
- Main feature 2/2: #21800
- Followup: #22084
Enable package CPFP
- Main feature 1/2: #22674
- Followup: #24310
- Followup: #23804
- Main feature 2/2: #24152
- short term bug fix: avoid the risk of below-minrelaytxfee transactions hanging around forever in the mempool #26933
RPC access
- #24836
- #26646
- #27609
- #28848
- #28950
- Followup: #29722
- Followup: #29735
Fuzzing and bug fixes
- #28450
- #28764
- #28825
- Bug fix: #28251
- Bug fix: #28471
- Bug fix: #28472

☑️ (2) Policy-Related Features: TRUC and limited package RBF

What we get: an opt-in policy for anti-pinning in single transaction or 1-parent-1-child package scenarios. Also, package CPFP of 0-fee parent and package RBF for restricted topologies prior to cluster mempool.

See PRs

☑️ (2a) Topologically Restricted Until Confirmation (v3) transaction policy

Note: BIP 431 isn't part of package relay. It just represents the topology for which we can build these features, i.e. bumping 0-fee parents and package RBF, without cluster mempool. It is also more robust for applications that would seek to use 1p1c package relay. Also see #29319 for its role in cluster mempool.

Main feature: #28948
Followup: #29424
Sibling Eviction: #29306
Decrease max vsize: #29873
Enable v3 on mainnet: #29496
Followup: #30272
Docs: https://github.com/bitcoin/bips/pull/1541

☑️ (2b) Package RBF for cluster size 2

Enable Package RBF for 1-parent-1-child situations
- Dependency: #22796
- Dependency: #22675
- Dependency: #22855
- Dependency: #29242
  - Followup: #29724
  - #29757
- Dependency: #30072
- #30066
- Main feature: #28984
- followup: #30295

Also see: Ephemeral Dust and Pay To Anchor (P2A) aka Ephemeral Anchors

☑️ (3) 1-parent-1-child package relay

What we get: package relay of 1-parent-1-child packages. Protocols like LN can use this to create 0-fee presigned transactions with a single, 0-value anchor output; 0-fee commitment transactions can replace each other using the fees of the child attached to the anchor. This should provide an adequate replacement for CPFP carve out, which is helpful for the next step (see #29319).

Opportunistically submit 1-parent-1-child packages
- Dependency: #29619
- Main feature: #28970
- Followup: #30012

(4) TxDownloadManager and orphan-handling improvements

All of this code directly contributes to package relay, whether it's BIP 331 or a different protocol.

Modularize TxDownloadManager + testing
- Dependency: #28785
- Dependency: #28199
- Dependency: #28364
- Dependency: #30111
  - Followup: #30507
- Main PR: #30110
  - Followup: #31190
  - WIP: one_honest_peer fuzzer
  - WIP: make internally thread-safe
Make orphanage more robust. See known orphanage problems.
- #30000
- #31397
  - Followup: #31666
- #31810
- #31829
- WIP: make TxDownloadManager internally thread-safe #28031
- WIP: token bucket orphanage protection

(5) more general package relay

Goals: propagate incentive-compatible packages that are more compelx than 1p1c, safely evaluate replacements within packages, handle orphans better.

This is deferred until #30289 is completed. Handling arbitrary ancestor packages (i.e. beyond 1p1c or child-with-parents-tree) is very complex. Also, there are various higher-priority issues with mempool that make accepting packages more difficult to reason about, and that we should fix before adding more general package relay.

Package validation and package RBF with less restrictive topologies
- #26711
- https://delvingbitcoin.org/t/post-clustermempool-package-rbf-per-chunk-processing/190
BIP 331 ancestor package relay for orphan-handling
- BIP: bitcoin/bips/pull/1382
- #27742
ancestor set + prefix?
sender-initiated package relay protocol using chunks (?)