Write-ahead log

<div class="demo"><div class="head"><b>WRITE-AHEAD LOG</b><span>UPDATE balance</span></div><div class="stage wal"><div class="step cell">1 · WAL</div><div class="step cell">2 · commit</div><div class="step cell">3 · page</div></div><div class="foot"><span id="walstatus">log record written first</span><span>crash → replay</span></div></div>

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let n=0;const s=['log record written first','commit acknowledged','data page updated'];function tick(){document.querySelectorAll('.wal .step').forEach((e,i)=>e.classList.toggle('on',i<=n));document.getElementById('walstatus').textContent=s[n];n=(n+1)%3}tick();const t=setInterval(tick,1050);document.querySelector('.demo').onclick=()=>{clearInterval(t);tick()}