113 lines
5.2 KiB
HTML
113 lines
5.2 KiB
HTML
<!doctype html>
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<html>
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<meta name="viewport" content="width=device-width, initial-scale=1" />
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<title>haunt98 posts</title>
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.markdown-body {
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box-sizing: border-box;
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<body class="markdown-body">
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<h2>
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<a href="index.html"><code>~</code></a>
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</h2>
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<h1 id="user-content-cache-shenanigan">
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<a class="heading-link" href="#cache-shenanigan"
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>Cache shenanigan<span
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aria-hidden="true"
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class="octicon octicon-link"
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></span
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></a>
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</h1>
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<p>
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My notes/mistakes/... when using cache (mainly Redis) from time to time
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</p>
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<p>My default strategy is:</p>
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<ul>
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<li>Write to database first then to cache second</li>
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<li>
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Read from cache first, if not found then read from database second, then
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re-write to cache
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</li>
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</ul>
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<div class="highlight highlight-source-mermaid">
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<pre><span class="pl-k">sequenceDiagram</span>
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<span class="pl-k">participant</span> <span class="pl-ent">other</span>
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<span class="pl-k">participant</span> <span class="pl-ent">service</span>
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<span class="pl-k">participant</span> <span class="pl-ent">cache</span>
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<span class="pl-k">participant</span> <span class="pl-ent">db</span>
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<span class="pl-ent">other </span><span class="pl-k">->></span> <span class="pl-ent">service</span><span class="pl-k">:</span> <span class="pl-s">get data</span>
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<span class="pl-k">activate</span> <span class="pl-ent">service</span>
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<span class="pl-ent">service </span><span class="pl-k">->></span> <span class="pl-ent">cache</span><span class="pl-k">:</span> <span class="pl-s">get data</span>
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<span class="pl-k">alt</span> <span class="pl-s">exist in cache</span>
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<span class="pl-ent">service </span><span class="pl-k">-->></span> <span class="pl-ent">other</span><span class="pl-k">:</span> <span class="pl-s">return data</span>
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<span class="pl-k">else</span> <span class="pl-s">not exist in cache</span>
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<span class="pl-ent">service </span><span class="pl-k">->></span> <span class="pl-ent">db</span><span class="pl-k">:</span> <span class="pl-s">get data</span>
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<span class="pl-k">alt</span> <span class="pl-s">exist data in db</span>
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<span class="pl-ent">service </span><span class="pl-k">-->></span> <span class="pl-ent">other</span><span class="pl-k">:</span> <span class="pl-s">return data</span>
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<span class="pl-k">else</span> <span class="pl-s">not exist data in db</span>
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<span class="pl-ent">service </span><span class="pl-k">-->></span> <span class="pl-ent">other</span><span class="pl-k">:</span> <span class="pl-s">return error not found</span>
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<span class="pl-k">end</span>
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<span class="pl-k">end</span>
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<span class="pl-k">deactivate</span> <span class="pl-ent">service</span>
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<span class="pl-ent">other </span><span class="pl-k">->></span> <span class="pl-ent">service</span><span class="pl-k">:</span> <span class="pl-s">set data</span>
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<span class="pl-k">activate</span> <span class="pl-ent">service</span>
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<span class="pl-ent">service </span><span class="pl-k">->></span> <span class="pl-ent">db</span><span class="pl-k">:</span> <span class="pl-s">set data</span>
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<span class="pl-ent">service </span><span class="pl-k">->></span> <span class="pl-ent">cache</span><span class="pl-k">:</span> <span class="pl-s">set data</span>
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<span class="pl-k">deactivate</span> <span class="pl-ent">service</span></pre>
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</div>
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<p>It's good for general cases, for example with CRUD action.</p>
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<p>
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The bad things happen when cache and database are not consistent. For
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example what happen if writing database OK then writing cache failed? Now
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database has new value, but cache has old value Then when we read again,
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we read cache first with old value, and that is disaster.
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</p>
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<h2 id="user-content-thanks">
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<a class="heading-link" href="#thanks"
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>Thanks<span aria-hidden="true" class="octicon octicon-link"></span
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></a>
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</h2>
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<ul>
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<li>
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<a
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href="https://danielw.cn/cache-consistency-with-database"
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rel="nofollow"
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>Cache Consistency with Database</a
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>
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</li>
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</ul>
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<div>
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Feel free to ask me via
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<a href="mailto:hauvipapro+posts@gmail.com">email</a> or
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<a rel="me" href="https://hachyderm.io/@haunguyen">Mastodon</a>.
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<br />Source code is available on
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<a href="https://github.com/haunt98/posts-go">GitHub</a>
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<a href="https://codeberg.org/yoshie/posts-go">Codeberg</a>
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<a href="https://git.sr.ht/~youngyoshie/posts-go">sourcehut</a>
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<a href="https://gitea.treehouse.systems/yoshie/posts-go">Treehouse</a>
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<a href="https://gitlab.com/youngyoshie/posts-go">GitLab</a>
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</div>
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</body>
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</html>
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