Access Lists · Warm Vs Cold · Eip-2929/2930 · Ethereum & Contracts Deep Lesson 21

Pre-Berlin, every SLOAD cost 800 gas. EIP-2929 repriced them to 2,100 cold (first access in a tx) and 100 warm (subsequent), making first-touch much more expensive. EIP-2930 added an optional access list on a transaction: declare upfront which addresses and slots you will touch, pay 1,900 gas per slot, and every access of those slots is warm. Net savings: 200 gas per access beyond the first.

Access lists pay off when a contract touches the same slot many times or wants to make gas costs more predictable. The demo computes the savings for six accesses across three unique slots.

The Reentrancy Reaper attacks — common mistakes

Forgetting access lists cost 1900 per slot — net loss if you touch each once

Adding slots you do not actually access

Confusing storage access pricing with code access pricing

Treating warm storage cost as the same as memory (memory is cheaper)

Boss battleCompute the gas saved by an access list for 6 accesses across 3 unique slots vs no access list.

Example code

<!doctype html><html><head><meta charset="utf-8"></head> <body style="background:#06040d;color:#e6e0ff;font-family:monospace;padding:20px"><pre id="o"></pre> <script> const COLD = 2100, WARM = 100, AL_COST = 1900; const accesses = ['slot1','slot2','slot1','slot3','slot2','slot3']; // 6 accesses, 3 unique const warmed = new Set(); let gasNoAL = 0; for(const a of accesses){ gasNoAL += warmed.has(a) ? WARM : COLD; warmed.add(a); } const unique = new Set(accesses); const gasWithAL = unique.size * AL_COST + accesses.length * WARM; const savings = gasNoAL - gasWithAL; document.getElementById('o').textContent = [ 'access pattern: ' + accesses.join(', ') + ' (' + accesses.length + ' accesses, ' + unique.size + ' unique)', '', 'WITHOUT access list:', ' ' + Array.from(unique).length + ' cold @ ' + COLD + ' + ' + (accesses.length - unique.size) + ' warm @ ' + WARM + ' = ' + gasNoAL.toLocaleString() + ' gas', '', 'WITH access list (pre-warm ' + unique.size + ' slots @ ' + AL_COST + '):', ' ' + (unique.size*AL_COST).toLocaleString() + ' AL + ' + (accesses.length*WARM).toLocaleString() + ' warm accesses = ' + gasWithAL.toLocaleString() + ' gas', '', 'savings: ' + savings.toLocaleString() + ' gas (~' + Math.round(100*savings/gasNoAL) + '%)' ].join('\n'); </script></body></html>

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access lists · warm vs cold · eip-2929/2930

Power-ups you unlock

The Reentrancy Reaper attacks — common mistakes

Example code