title: Shared hit cache in postgreSQL
body: <p>I'm experimenting with the EXPLAIN command and trying to find out what the <code>shared hit</code> is.</p>
  
  <pre><code>Seq Scan on foo  (cost=0.00..18334.00 rows=1000000 width=37) (actual time=0.030..90.500 rows=1000000 loops=1)
    Buffers: shared hit=512 read=7822
  Total runtime: 116.080 ms
  </code></pre>
  
  <p>I've noticed that the more shared hit number we have the faster a query is being executed. But what is that? As far as I got, <code>shared read</code> is just reading from a physical storage like <code>RAID</code> or <code>SSD</code>. But why is the <code>shared hit</code> faster? Is it stored inside RAM or where? </p>