feat: more draft

docs/2024-01-20-backend-thinking.html

@@ -453,34 +453,99 @@
     </ul>
     <h2>
       <a
-        id="user-content-system-design"
+        id="user-content-system-design-concept"
         class="anchor"
         aria-hidden="true"
         tabindex="-1"
-        href="#system-design"
+        href="#system-design-concept"
         ><span aria-hidden="true" class="octicon octicon-link"></span></a
-      >System Design
+      >System Design Concept
     </h2>
-    <h2>
+    <p>Start with basic: getting data from database.</p>
+    <div class="highlight highlight-source-mermaid">
+      <pre><span class="pl-k">sequenceDiagram</span>
+    <span class="pl-k">participant</span> <span class="pl-ent">service</span>
+    <span class="pl-k">participant</span> <span class="pl-ent">database</span>
+    
+    <span class="pl-ent">service </span><span class="pl-k">-&gt;&gt;</span> <span class="pl-ent">database</span><span class="pl-k">:</span> <span class="pl-s">get (100ms)</span></pre>
+    </div>
+    <p>Getting data from cache first, then database later.</p>
+    <div class="highlight highlight-source-mermaid">
+      <pre><span class="pl-k">sequenceDiagram</span>
+    <span class="pl-k">participant</span> <span class="pl-ent">service</span>
+    <span class="pl-k">participant</span> <span class="pl-ent">cache</span>
+    <span class="pl-k">participant</span> <span class="pl-ent">database</span>
+    
+    <span class="pl-ent">service </span><span class="pl-k">-&gt;&gt;</span> <span class="pl-ent">cache</span><span class="pl-k">:</span> <span class="pl-s">get (5ms)</span>
+    <span class="pl-k">alt</span> <span class="pl-s">not exist in cache</span>
+        <span class="pl-s">service -&gt;&gt; database: get (100ms)</span>
+    <span class="pl-k">end</span></pre>
+    </div>
+    <p>
+      If data is already in cache, we can get it so fast (5ms), nearly instant.
+      But if not, we hit penalty, must get database after then re-update cache
+      if need (&gt;105ms). The best case is worth even if hitting penalty
+      sometimes.
+    </p>
+    <p>Basic cache strategy: combine Write Through and Read Through</p>
+    <div class="highlight highlight-source-mermaid">
+      <pre><span class="pl-k">sequenceDiagram</span>
+    <span class="pl-k">participant</span> <span class="pl-ent">service</span>
+    <span class="pl-k">participant</span> <span class="pl-ent">cache</span>
+    <span class="pl-k">participant</span> <span class="pl-ent">database</span>
+    
+    <span class="pl-k">note over </span><span class="pl-ent">service</span><span class="pl-sg">,</span><span class="pl-ent">database</span>: <span class="pl-ent">Read Through</span>
+    <span class="pl-ent">service </span><span class="pl-k">-&gt;&gt;</span> <span class="pl-ent">cache</span><span class="pl-k">:</span> <span class="pl-s">get</span>
+    <span class="pl-k">alt</span> <span class="pl-s">not exist in cache</span>
+        <span class="pl-s">service -&gt;&gt; database: get</span>
+        <span class="pl-s">service -&gt;&gt; cache: set</span>
+    <span class="pl-k">end</span>
+
+    <span class="pl-k">note over </span><span class="pl-ent">service</span><span class="pl-sg">,</span><span class="pl-ent">database</span>: <span class="pl-ent">Write Through</span>
+    <span class="pl-ent">service </span><span class="pl-k">-&gt;&gt;</span> <span class="pl-ent">database</span><span class="pl-k">:</span> <span class="pl-s">set</span>
+    <span class="pl-ent">service </span><span class="pl-k">-&gt;&gt;</span> <span class="pl-ent">cache</span><span class="pl-k">:</span> <span class="pl-s">set</span></pre>
+    </div>
+    <h3>
       <a
-        id="user-content-performance"
+        id="user-content-references-2"
         class="anchor"
         aria-hidden="true"
         tabindex="-1"
-        href="#performance"
+        href="#references-2"
         ><span aria-hidden="true" class="octicon octicon-link"></span></a
-      >Performance
+      >References
-    </h2>
+    </h3>
-    <h2>
+    <ul>
-      <a
+      <li>
-        id="user-content-security"
+        <a href="https://apenwarr.ca/log/20201227" rel="nofollow"
-        class="anchor"
+          >Systems design explains the world: volume 1</a
-        aria-hidden="true"
+        >
-        tabindex="-1"
+      </li>
-        href="#security"
+      <li>
-        ><span aria-hidden="true" class="octicon octicon-link"></span></a
+        <a href="https://apenwarr.ca/log/20230415" rel="nofollow"
-      >Security
+          >Systems design 2: What we hope we know</a
-    </h2>
+        >
+      </li>
+      <li>
+        <a
+          href="https://martin.kleppmann.com/2016/02/08/how-to-do-distributed-locking.html"
+          rel="nofollow"
+          >How to do distributed locking</a
+        >
+      </li>
+      <li>
+        <a href="http://antirez.com/news/101" rel="nofollow"
+          >Is Redlock safe?</a
+        >
+      </li>
+      <li>
+        <a
+          href="https://danielw.cn/cache-consistency-with-database#cache-patterns"
+          rel="nofollow"
+          >Cache Consistency with Database</a
+        >
+      </li>
+    </ul>
     <h2>
       <a
         id="user-content-damage-control"
@@ -491,7 +556,6 @@
         ><span aria-hidden="true" class="octicon octicon-link"></span></a
       >Damage control
     </h2>
-    <p>TODO: Take care incident</p>
     <h2>
       <a
         id="user-content-bonus"

posts/2024-01-20-backend-thinking.md

@@ -207,16 +207,66 @@ Some tips:
 - [Imaginary Problems Are the Root of Bad Software](https://cerebralab.com/Imaginary_Problems_Are_the_Root_of_Bad_Software)
 - [Speed up writing Go test ASAP](https://haunt98.github.io/posts-go/2022-12-25-go-test-asap.html)
 
-## System Design
+## System Design Concept
 
-## Performance
+Start with basic: getting data from database.
 
-## Security
+```mermaid
+sequenceDiagram
+    participant service
+    participant database
+    
+    service ->> database: get (100ms)
+```
+
+Getting data from cache first, then database later.
+
+```mermaid
+sequenceDiagram
+    participant service
+    participant cache
+    participant database
+    
+    service ->> cache: get (5ms)
+    alt not exist in cache
+        service ->> database: get (100ms)
+    end
+```
+
+If data is already in cache, we can get it so fast (5ms), nearly instant. But if
+not, we hit penalty, must get database after then re-update cache if need
+(>105ms). The best case is worth even if hitting penalty sometimes.
+
+Basic cache strategy: combine Write Through and Read Through
+
+```mermaid
+sequenceDiagram
+    participant service
+    participant cache
+    participant database
+    
+    note over service,database: Read Through
+    service ->> cache: get
+    alt not exist in cache
+        service ->> database: get
+        service ->> cache: set
+    end
+
+    note over service,database: Write Through
+    service ->> database: set
+    service ->> cache: set
+```
+
+### References
+
+- [Systems design explains the world: volume 1](https://apenwarr.ca/log/20201227)
+- [Systems design 2: What we hope we know](https://apenwarr.ca/log/20230415)
+- [How to do distributed locking](https://martin.kleppmann.com/2016/02/08/how-to-do-distributed-locking.html)
+- [Is Redlock safe?](http://antirez.com/news/101)
+- [Cache Consistency with Database](https://danielw.cn/cache-consistency-with-database#cache-patterns)
 
 ## Damage control
 
-TODO: Take care incident
-
 ## Bonus
 
 - [IntelliJ IDEA Ultimate](https://www.jetbrains.com/idea/download/): Java