Everyone who has used bitcoin has made use of the mempool, or a mempool. So what is the mempool?

Well technically, there is no such thing as “the” mempool. Every individual full Bitcoin node operates its own mempool, a cache of valid bitcoin transactions that have been broadcast to the network but have yet to be confirmed in a block. Nodes exchange messages with each other to see what transactions they have or not, and exchange ones they don’t have. 

Each mempool is its own independent island essentially, with its own set of unconfirmed transactions, and sometimes its own configuration variables and settings. There is a size value to configure, set to 300 MB by default. In…

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