PostgreSQL concurrent repack

<div class="demo"><div class="head"><b>REPACK CONCURRENTLY</b><span>PG 19 beta</span></div><div class="stage repack"><div class="blockrow"><span>old</span><i></i><i></i><i></i><i></i></div><div class="blockrow compact"><span>new</span><i></i><i></i><i></i><i></i></div><div class="traffic"><b>READ</b><b>WRITE</b></div></div><div class="foot"><span id="repackstatus">copy block 1 / 4</span><span>traffic continues</span></div></div>

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let n=0;function tick(){document.querySelectorAll('.compact i').forEach((e,i)=>e.classList.toggle('on',i<=n));document.getElementById('repackstatus').textContent=n===3?'compact copy ready':'copy block '+(n+1)+' / 4';n=(n+1)%4}tick();const t=setInterval(tick,650);document.querySelector('.demo').onclick=()=>{clearInterval(t);tick()}