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From Apache Wiki <wikidi...@apache.org>
Subject [Hadoop Wiki] Update of "Hbase/Troubleshooting" by AndrewPurtell
Date Tue, 08 Dec 2009 22:56:45 GMT
Dear Wiki user,

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The "Hbase/Troubleshooting" page has been changed by AndrewPurtell.


   1. [[#13|Problem: Long client pauses under high load; or deadlock if using THBase]]
   1. [[#14|Problem: Zookeeper does not seem to work on Amazon EC2]]
   1. [[#15|Problem: General operating environment issues -- zookeeper session timeouts, regionservers
shutting down, etc.]]
+  1. [[#16|Problem: Scanner performance is low]]
  == 1. Problem: Master initializes, but Region Servers do not ==
@@ -229, +230 @@

  == Resolution ==
   * See the [[http://wiki.apache.org/hadoop/ZooKeeper/Troubleshooting ZooKeeper Operating
Environment Troubleshooting]] page.  It has suggestions and tools for checking disk and networking
performance; i.e. the operating environment your zookeeper and hbase are running in.  ZooKeeper
is the cluster's "canary".  It'll be the first to notice issues if any so making sure its
happy is the short-cut to a humming cluster.
+ <<Anchor(16)>>
+ == 16. Problem: Scanner performance is low ==
+ == Causes ==
+ Default scanner caching (prefetching) is set to 1. The default is low because if a job takes
too long processing, a scanner can time out, which causes unhappy jobs/people/emails. See
item #10 above.
+ == Resolution ==
+  * Increase the amount of prefetching on the scanner, to 10, or 100, or 1000, as appropriate
for your workload:
+ [[http://hadoop.apache.org/hbase/docs/r0.20.2/api/org/apache/hadoop/hbase/client/HTable.html#scannerCaching
+  * This change can be accomplished globally by setting the hbase.client.scanner.caching
property in hbase-site.xml to the desired value.

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