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From Apache Wiki <wikidi...@apache.org>
Subject [Hadoop Wiki] Update of "Hbase/Troubleshooting" by AndrewPurtell
Date Wed, 08 Apr 2009 17:51:45 GMT
Dear Wiki user,

You have subscribed to a wiki page or wiki category on "Hadoop Wiki" for change notification.

The following page has been changed by AndrewPurtell:
http://wiki.apache.org/hadoop/Hbase/Troubleshooting

The comment on the change is:
some inital comments/recommendations about Amazon EC2 deployments 

------------------------------------------------------------------------------
   1. [#5 Problem: "xceiverCount 258 exceeds the limit of concurrent xcievers 256"]
   1. [#6 Problem: "No live nodes contain current block"]
   1. [#7 Problem: DFS instability and/or regionserver lease timeouts]
+  1. [#8 Problem: Instability on Amazon EC2]
  
  [[Anchor(1)]]
  == 1. Problem: Master initializes, but Region Servers do not ==
@@ -127, +128 @@

      * [http://java.sun.com/javase/technologies/hotspot/gc/gc_tuning_6.html Tuning garbage
collector in Java SE 6]
   * For Java SE 6, some users have had success with {{{ -XX:+UseConcMarkSweepGC -XX:+CMSIncrementalMode
}}}
  
+ [[Anchor(8)]]
+ == 8. Problem: Instability on Amazon EC2 ==
+  * Various problems suggesting overloading on Amazon EC2 deployments: Scanner timeouts,
problems locating HDFS blocks, missed heartbeats, "We slept xxx ms, ten times longer than
scheduled" messages, and so on. 
+  * These problems continue after following the other relevant advice on this page. 
+  * Or, you are trying to use Small or Medium instance types. (Do not.)
+ === Causes ===
+  * Hadoop and HBase daemons require 1GB heap, therefore RAM, per daemon. For load intensive
environments, HBase regionservers may require more heap than this. There must be enough available
RAM to comfortably hold the working sets of all Java processes running on the instance. This
includes any mapper or reducer tasks which may run co-located with system daemons. Small and
Medium instances do not have enough available RAM to contain typical Hadoop+HBase deployments.

+  * Hadoop and HBase daemons are latency sensitive. There should be enough free RAM so no
swapping occurs. Swapping during garbage collection may cause JVM threads to be suspended
for a critically long time. Also, there should be sufficient virtual cores to service the
JVM threads whenever they become runnable. Large instances have two virtual cores, so they
can run HDFS and HBase daemons concurrently, but nothing more. X-Large instances have four
virtual cores, so they can run in addition to HDFS and HBase daemons two mappers or reducers
concurrently. Configure TaskTracker concurrency limits accordingly, or separate mapreduce
computation from storage functions. 
+ === Resolution ===
+  * Use Large instances for HDFS and HBase storage tasks.
+  * Use X-Large instances if you are also running mappers and reducers co-located with system
daemons.
+  * Consider splitting storage and computational function over disjoint instance sets. 
+ 

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