title: Why do NoSql databases scale better than relational databases? How should I choose between them?
body: <p>By nosql databases I mean something like mongodb or dynamodb
  I've been trying to find why NoSql dbs usually are usually better at horizontal scaling than relational dbs, and how to choose between them</p>
  <p>I have looked into many videos and posts that tell us the &quot;SQL vs NoSQL&quot;. Most of them end up talking about &quot;Normalization vs Denormalization&quot;.</p>
  <p>Here are some questions I am still confused about.</p>
  <p>1.
  Many people said that relational dbs have to follow ACID so they are bad at horizontal scaling. But ACID is about transaction, we can always choose not to use any transaction, right? I know not many people do this, but if we denormalized tables enough, would it be like NoSQL dbs where we almost don't use any transaction?. And many NoSql dbs now have transactions too.</p>
  <p>2.
  I know denormalization is probably good for horizontal scaling, because if data are
  spreaded across many nodes(machines), it'll be hard to do table joining(or transaction).
  But like transaction, we can choose not to use any table join.</p>
  <p>The only thing I can think of is NoSQL are schema-free, it is easier to add new fields(columns) than RDB.</p>
  <p>What I am trying to ask are<br>
  why is a &quot;Denormalized NoSQL db&quot; better than a &quot;Denormalized relational db&quot; ?<br>
  why is a &quot;Normalized NoSQL db&quot; worse than a &quot;Normalized relational db&quot; ?<br>
  what's the real thing that prevents relational database from denormalization?<br></p>
  <p>I've read this post<br>
  <a href="https://softwareengineering.stackexchange.com/questions/194340/why-are-nosql-databases-more-scalable-than-sql">https://softwareengineering.stackexchange.com/questions/194340/why-are-nosql-databases-more-scalable-than-sql</a><br>
  It says <br>
  &quot;&quot;The SQL API lacks a mechanism to describe queries where ACID's requirements are relaxed. This is why the BASE databases are all NoSQL.&quot;&quot;<br>
  Could anyone give me an example of this?</p>
  <hr />
  <p>Sorry for not being specific</p>
  <p>By NoSQL databases I mean something like mongodb</p>