title: convert pg_LSN to wAL postgresql
body: <p>I have configured the streaming replication using the replication slot. I have checked the view <code>pg_replication_slots</code> which contain </p>
  
  <pre><code>restart_lsn pg_lsn
  </code></pre>
  
  <p>The address (<code>LSN</code>) of oldest <code>WAL</code> which still might be required by the consumer of this slot and thus won't be automatically removed during checkpoints.</p>
  
  <p>I want to find the minimum <code>WAL</code> required by my standby before the master archive the same. </p>
  
  <p>I thought of converting the <code>LSN</code> to <code>WAL</code> but I am not able to find any command. Please help me with this.</p>