title: How to check if a database link is valid in Oracle?
body: <p>I have a main database with only setup data at the headquarter and several databases at different branches.I created a database link for each branch server.</p>
  
  <p>In some case I would like to query all the valid links (as some links could be invalid due to connection problems or anything else),so my question is How to check if the database link is valid without getting in Connection timeout problems. Is there a SQL statement to let the oracle main server do that check and return only the valid database links?</p>