NotATether: Create Package relay stub (1p1c / mempool package policy)

2026-09-12T03:44:21Z

Create Package relay stub (1p1c / mempool package policy)

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'''Package relay''' is a transaction-relay and [[Mempool|mempool]]-acceptance policy in which a group of related transactions is evaluated together rather than one at a time. The usual case is a parent that pays little or no fee and a child that pays enough for both (child-pays-for-parent). Without package relay, a node that enforces a minimum relay feerate drops the parent and never learns about the child.

Bitcoin P2P transaction relay historically advertised one txid at a time. A peer who receives a transaction below <code>minrelaytxfee</code> rejects it. Contracting protocols that sign zero-fee or low-fee parents and bump them with a child therefore fail to propagate on nodes that have not already accepted the parent by other means. Local <code>submitpackage</code> allowed submitting a package to one node, but peers could not request packages from each other.

A package is a list of transactions in topological order. Validation applies consensus rules to each transaction, then package-level policy: the package feerate must meet the mempool minimum, transactions must not conflict with one another, and for the limited 1-parent-1-child (1p1c) case the graph must be one parent and one child. The parent may be below the minimum relay feerate if the package as a whole is not.

On the P2P network, when a node rejects a transaction as too low-feerate, it may remember the txid briefly. If a later child arrives that spends that txid, the node requests the parent again and validates the pair. Bitcoin Core 28.0 implemented this opportunistic 1p1c path and allowed [[TRUC]] parents to pay zero fee. Bitcoin Core 31.0 extended zero-fee parents to non-TRUC 1p1c packages. A child may have additional parents that are already in the mempool. A child with several unconfirmed missing parents is not covered by this limited P2P feature.

Package RBF (documented on [[Mempool#Package RBF|Mempool]]) lets a package replace in-mempool transactions when the replacement is incentive-compatible. [[Ephemeral_anchor|Ephemeral anchor]] constructions depend on package relay: a zero-fee parent with a dust pay-to-anchor output is not accepted alone and must arrive with its child.

== See also ==
* [[Mempool]]
* [[TRUC]]
* [[Replace by fee]]
* [[Ephemeral_anchor|Ephemeral anchor]]
* [[Transaction pinning]]

== External links ==
* [https://bitcoinops.org/en/topics/package-relay/ Bitcoin Optech: Package relay]
* [https://bitcoincore.org/en/releases/28.0/ Bitcoin Core 28.0 release notes]
* [https://bitcoincore.org/en/releases/31.0/ Bitcoin Core 31.0 release notes]

[[Category:Technical]]

Package relay - Revision history

NotATether: Create Package relay stub (1p1c / mempool package policy)