title: What does "LANGUAGE plpgsql VOLATILE COST 100" mean in functions
body: <p>I am new to Postgres triggers. I saw an example of triggers on <a href="http://www.postgresql.org/message-id/4D8CC8D9.2000103@lpnhe.in2p3.fr/" rel="noreferrer">www.postgresql.org</a> and I didn't understand what is <code>LANGUAGE plpgsql VOLATILE COST 100;</code> at the end of the trigger-function.</p>
  
  <p>What is the use of this line?</p>
  
  <p>I saw a question related to this <a href="https://stackoverflow.com/q/12577004/2764279">what does “LANGUAGE 'plpgsql' VOLATILE” mean?</a>
  but it is only about <code>volatile</code>, what is <code>cost 100</code> and <code>language</code> in this line?</p>