[HBASE-1918] Don't do DNS resolving in .META. scanner for each row

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 0.19.3, 0.20.1
• Fix Version/s: 0.20.2, 0.90.0
• Hadoop Flags: Reviewed
• Assignee: Jean-Daniel Cryans
• Reporter: Jean-Daniel Cryans
• Created: 19/Oct/09 18:55
• Updated: 12/Oct/12 06:13
• Resolved: 20/Oct/09 03:53

Description

While debugging a slow HBase on my new Mac, I found that my issue was that DNS resolving was taking 10 seconds. Since Java 1.5, many people complained about that and there's even a very commented issue (http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=5092063) that's closed but still "active". In fact the real issue here is that when you a bad DNS resolving (my router was acting on me, it's dead now) it waits for 10 seconds or something like that (see previous link). So I was running PE and my meta scanner was being slower and slower. In fact, everything was slow, even starting the shell. So using jps I found that we are resolving DNS for each scanned row in META in checkAssigned here:

if (sa != null && sa.length() > 0) {
  serverName = HServerInfo.getServerName(sa, sc);
} 
HServerInfo storedInfo = null;

HSI.getServerName here creates a new HServerAddress which resolves DNS in its depths and it's not even necessary, we use it just to split the server IP and port.