Ledger LandISSUE #18 of 90

mempool · the pending pool

BlockyVSDouble-Spend Dan

Blocky saysThe mempool is the waiting room of unconfirmed transactions before they’re put in a block.

When you broadcast a transaction, it lands in nodes' mempools (memory pools) — pending, not yet in a block. Block producers pick transactions from the mempool, usually favoring higher fees. During congestion the mempool swells and low-fee transactions wait (or get dropped). The mempool is public, which is what makes front-running and MEV possible.

Power-ups you unlock

Pending, unconfirmed transactions
Producers pick from it, favoring high fees
Congestion → backlog, low-fee txs wait
Public mempool enables front-running/MEV

Double-Spend Dan attacks — common mistakes

Assuming a broadcast tx is already final
Underpaying fees during congestion
Forgetting the mempool is publicly visible

Boss battleExplain why a low-fee transaction can sit in the mempool for hours.

Example code

<!doctype html><html><head><meta charset="utf-8"></head>
<body style="background:#06040d;color:#e6e0ff;font-family:monospace;padding:20px"><pre>broadcast → mempool (pending, public)
producer picks high-fee txs first
low fee + congestion → long wait</pre></body></html>

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