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I was tracking a transaction using a Bitcoin Core command. I was able to extract info on whether the transaction had entered the mempool.

Among the information I got were details such as "the block height when the transaction entered the mempool".

Does this mean that blocks 'carry' unvalidated/unverified, but unconfirmed, transactions?

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Blocks don't "carry" any unconfirmed transactions. By definition, a transaction is confirmed when it's included in a block.

Importantly, the block height when the transaction entered the mempool might be different from one mempool to another, as transactions take time to propagate through the network and a new block might be mined while it's propagating. It will also be different for transactions that your node receives from its peers when it's starting again after a downtime, since those transactions may have been in their mempool for many blocks already.

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  • Thanks for this. Understood, blocks don't "carry" any unconfirmed transactions. But how then do transactions enter the mempool? I guess I am particularly confused by the mention of "the block height" when discussing transactions entering the mempool.
    – StatsScared
    Commented May 18, 2022 at 17:49
  • @StatsScared Nodes relay transactions through the peer-to-peer network. To emphasize a point from my answer, there's no such thing as "the mempool", every node maintains its own mempool for storing received transactions that are waiting to be confirmed, and two mempools don't necessarily have the same transactions.
    – Vojtěch Strnad
    Commented May 19, 2022 at 22:23
  • Thanks, @VojtěchStrnad. But I guess this make me wonder then. What is ‘the’ mempool references in sites like these: mempool.space?
    – StatsScared
    Commented May 20, 2022 at 20:28
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    @StatsScared Mempool explorers simply run their own Bitcoin node and offer its mempool for inspection. (mempool.space in particular is open source and you can easily run it over your own node, which removes trust and increases privacy.) Calling it 'the' mempool is just a simplification stemming from the fact that two nodes running the default mempool options and standardness policy will have very similar mempools.
    – Vojtěch Strnad
    Commented May 20, 2022 at 22:47
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    @StatsScared Yes, by "block" I don't mean just any block but specifically a block that is a part of the longest chain.
    – Vojtěch Strnad
    Commented May 31, 2022 at 14:09

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