[Hadoop Wiki] Trivial Update of "Hbase/Troubleshooting" by JeanDanielCryans

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The "Hbase/Troubleshooting" page has been changed by JeanDanielCryans.
http://wiki.apache.org/hadoop/Hbase/Troubleshooting?action=diff&rev1=39&rev2=40

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  <<Anchor(9)>>
  == 9. Problem: ZooKeeper SessionExpired events ==
+  * Master or Region Servers shutting down with messages like those in the logs:
-  * Master or RegionServers reinitialize their ZooKeeper wrappers after receiving SessionExpired events.
-  * Master or RegionServer ephemeral nodes disappear while the node is still otherwise functional.
-  * Messages those in the logs:
  {{{
  WARN org.apache.zookeeper.ClientCnxn: Exception 
  closing session 0x278bd16a96000f to sun.nio.ch.SelectionKeyImpl@355811ec
@@ -186, +184 @@

  === Causes ===
   * The JVM is doing a long running garbage collecting which is pausing every threads (aka "stop the world").
   * Since the region server's local zookeeper client cannot send heartbeats, the session times out.
+  * By design, we shut down any node that isn't able to contact the Zookeeper ensemble after getting a timeout so that it stops serving data that may already be assigned elsewhere.
  === Resolution ===
   * Make sure you give plenty of RAM (in hbase-env.sh), the default of 1GB won't be able to sustain long running imports.
   * Make sure you don't swap, the JVM never behaves well under swapping.