Multi-version concurrency control

<div class="demo"><div class="head"><b>ROW VERSIONS</b><span>item 7</span></div><div class="stage versions"><div class="reader"><div class="pill">old reader</div><div class="cell old">v1 · 100</div></div><div class="reader"><div class="pill">new reader</div><div class="cell fresh">v2 · 120</div></div></div><div class="foot"><span id="mvccstatus">old snapshot → v1</span><span>writer can continue</span></div></div>

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let n=0;function tick(){document.querySelector('.old').classList.toggle('on',!n);document.querySelector('.fresh').classList.toggle('on',!!n);document.getElementById('mvccstatus').textContent=n?'new snapshot → v2':'old snapshot → v1';n=1-n}tick();const t=setInterval(tick,1200);document.querySelector('.demo').onclick=()=>{clearInterval(t);tick()}