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In this episode of The Van Wirdum Sjorsnado, host Aaron van Wirdum and Sjors Provoost discussed Bitcoin mempools, Child Pays For Parent (CPFP) and a package exchange.
The project that Gloria Zhao will be working on as part of her Brink fellowship, announced earlier this week, is a package relay that would make the Lightning Network more resilient (among other benefits). Mempools are collections of unconfirmed transactions stored by nodes, from which they send transactions to peers. Miners usually select the transactions from their mempools that include the highest fees, to include these in the blocks they dig.
However, Mempools can go full and at that point transactions that pay the lowest fees are thrown out. This is actually a problem in the context of CPFP, a trick that allows consumers to accelerate low-fee transactions by spending the coins of those transactions in a new transaction with a high fee to compensate them. Bricks like these can be especially important in the context of time-sensitive protocols like the Lightning Network.
In this chapter, van Wirdum and Provoost explained how a package exchange could enable CPFP, even in cases where low-fee transactions are dropped from mempools, by bundling transactions in packages. And they are exploring why this might be easier said than done.