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Update 缓存.md

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补一张时序图，说明先删除缓存再更新数据库时，读请求会把旧值写回缓存。
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CyC2018
2026-10-25 18:52:37 +08:00
parent c6c805e4f8
commit a541d18c71
3 changed files with 54 additions and 0 deletions
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tools/diagram/src/cache-aside-race.svg
+52
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<svg xmlns="http://www.w3.org/2000/svg" width="520" height="322" viewBox="0 0 520 322">
<style>
text { font-family: "PingFang SC", "Microsoft YaHei", Helvetica, Arial, sans-serif; fill: #666; font-size: 13px; }
.head { font-weight: bold; text-anchor: middle; }
.msg { text-anchor: middle; font-size: 12px; }
.note { font-size: 12px; fill: #C0605A; }
.ok { fill: #6A9F68; }
.title { font-weight: bold; font-size: 15px; fill: #777; text-anchor: middle; }
.life { stroke: #BBB; stroke-width: 1; stroke-dasharray: 4 4; }
.arrow { stroke: #666; stroke-width: 1.3; fill: none; marker-end: url(#a); }
.reply { stroke-dasharray: 5 4; }
.lost { stroke: #C0605A; marker-end: url(#x); }
.shadow { fill: #C0C0C0; }
</style>
<defs>
<marker id="a" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="7" markerHeight="7" orient="auto">
<path d="M1,1 L9,5 L1,9" fill="none" stroke="#666" stroke-width="1.6"/>
</marker>
<marker id="x" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="7" markerHeight="7" orient="auto">
<path d="M1,1 L9,5 L1,9" fill="none" stroke="#C0605A" stroke-width="1.6"/>
</marker>
</defs>
<rect width="100%" height="100%" fill="#FFFFFF"/>
<text x="260" y="28" class="title">先删除缓存再更新数据库</text>
<line x1="65" y1="76" x2="65" y2="302" class="life"/>
<line x1="195" y1="76" x2="195" y2="302" class="life"/>
<line x1="325" y1="76" x2="325" y2="302" class="life"/>
<line x1="455" y1="76" x2="455" y2="302" class="life"/>
<rect x="32" y="48" width="72" height="30" rx="6" class="shadow"/>
<rect x="29" y="45" width="72" height="30" rx="6" fill="#B0E3E6"/>
<text x="65" y="64.5" class="head">写请求</text>
<rect x="162" y="48" width="72" height="30" rx="6" class="shadow"/>
<rect x="159" y="45" width="72" height="30" rx="6" fill="#B1DDF0"/>
<text x="195" y="64.5" class="head">缓存</text>
<rect x="292" y="48" width="72" height="30" rx="6" class="shadow"/>
<rect x="289" y="45" width="72" height="30" rx="6" fill="#B1DDF0"/>
<text x="325" y="64.5" class="head">数据库</text>
<rect x="422" y="48" width="72" height="30" rx="6" class="shadow"/>
<rect x="419" y="45" width="72" height="30" rx="6" fill="#B0E3E6"/>
<text x="455" y="64.5" class="head">读请求</text>
<line x1="69" y1="100" x2="191" y2="100" class="arrow"/>
<text x="130" y="94" class="msg">① 删除缓存</text>
<line x1="451" y1="136" x2="199" y2="136" class="arrow"/>
<text x="380" y="130" class="msg">② 读缓存未命中</text>
<line x1="451" y1="172" x2="329" y2="172" class="arrow"/>
<text x="390" y="166" class="msg">③ 读到旧值</text>
<line x1="69" y1="208" x2="321" y2="208" class="arrow"/>
<text x="120" y="202" class="msg">④ 更新为新值</text>
<line x1="451" y1="244" x2="199" y2="244" class="arrow"/>
<text x="380" y="238" class="msg">⑤ 把旧值写入缓存</text>
<text x="260" y="284" class="note" text-anchor="middle">缓存中一直是旧值，直到被删除或过期</text>
</svg>
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