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From Apache Wiki <wikidi...@apache.org>
Subject [Hadoop Wiki] Update of "Hbase/Troubleshooting" by AndrewPurtell
Date Fri, 18 Dec 2009 18:58:08 GMT
Dear Wiki user,

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

The "Hbase/Troubleshooting" page has been changed by AndrewPurtell.
http://wiki.apache.org/hadoop/Hbase/Troubleshooting?action=diff&rev1=34&rev2=35

--------------------------------------------------

   1. [[#16|Problem: Scanner performance is low]]
   1. [[#17|Problem: My shell or client application throws lots of scary exceptions during
normal operation]]
  
+ 
  <<Anchor(1)>>
  == 1. Problem: Master initializes, but Region Servers do not ==
   * Master's log contains repeated instances of the following block:
@@ -50, +51 @@

  127.0.0.1		localhost.localdomain localhost
  ::1		localhost6.localdomain6 localhost6
  }}}
+ 
+ 
  <<Anchor(2)>> 
  == 2. Problem: Created Root Directory for HBase through Hadoop DFS ==
   * On Startup, Master says that you need to run the hbase migrations script. Upon running
that, the hbase migrations script says no files in root directory.
@@ -57, +60 @@

   * HBase expects the root directory to either not exist, or to have already been initialized
by hbase running a previous time. If you create a new directory for HBase using Hadoop DFS,
this error will occur.
  === Resolution ===
   * Make sure the HBase root directory does not currently exist or has been initialized by
a previous run of HBase. Sure fire solution is to just use Hadoop dfs to delete the HBase
root and let HBase create and initialize the directory itself.
+ 
  
  <<Anchor(3)>>
  == 3. Problem: Replay of hlog required, forcing regionserver restart ==
@@ -77, +81 @@

  === Causes ===
   * RPC timeouts may happen because of a IO contention which blocks processes during file
swapping.
  === Resolution ===
+  * Configure your system to avoid swapping. Set vm.swappiness to 0. (http://kerneltrap.org/node/1044)
+ 
  
  <<Anchor(4)>>
  == 4. Problem: On migration, no files in root directory ==
@@ -86, +92 @@

  === Resolution ===
   * Make sure the HBase root directory does not currently exist or has been initialized by
a previous run of HBase. Sure fire solution is to just use Hadoop dfs to delete the HBase
root and let HBase create and initialize the directory itself.
  
- == Problem: lots of DFS error regarding can not find block from live nodes ==
-  * Under heavy read load, you may see lots of DFSClient complains about no live nodes hold
a particular block. And, hadoop DataNode logs show xceiverCount exceed the limit (256)
- 
- === Causes ===
-  * not enough xceiver thread on DataNode to serve the traffic
- 
- === Resolution ===
-  * Either reduce the load or set dfs.datanode.max.xcievers (hadoop-site.xml) to a larger
value than the default (256). Note that in order to change the tunable, you need 0.17.2 or
0.18.0 (HADOOP-3859).
  
  <<Anchor(5)>>
  == 5. Problem: "xceiverCount 258 exceeds the limit of concurrent xcievers 256" ==
@@ -101, +99 @@

  === Causes ===
   * An upper bound on connections was added in Hadoop (HADOOP-3633/HADOOP-3859).
  === Resolution ===
-  * Up the maximum by setting '''dfs.datanode.max.xcievers''' (sic).  See [[http://mail-archives.apache.org/mod_mbox/hadoop-hbase-user/200810.mbox/%3C20126171.post@talk.nabble.com%3E|message
from jean-adrien]] for some background.
+  * Up the maximum by setting '''dfs.datanode.max.xcievers''' (sic).  See [[http://mail-archives.apache.org/mod_mbox/hadoop-hbase-user/200810.mbox/%3C20126171.post@talk.nabble.com%3E|message
from jean-adrien]] for some background. Values of 2048 or 4096 are common. 
  
  
  <<Anchor(6)>>
@@ -133, +131 @@

  2009-02-24 10:01:36,472 WARN org.apache.hadoop.hbase.regionserver.HRegionServer: unable
to report to master for xxx milliseconds - retrying
  }}}
  === Causes ===
-  * Excessive connection establishment latency (HRPC sets up connections on demand)
   * Slow host name resolution
+  * Very long garbage collector task for the RegionServer JVM: The ''default garbage collector''
of the HotspotTM JavaTM Virtual Machine runs a ''full gc'' on the ''old space'' when the memory
space is full, which can represent about 90% of the allocated heap space. During this task,
the running program is stopped, the timers as well. If the heap space is mostly in the swap
partition, and moreover if it is larger than the physical memory, the subsequent swap can
yield to I/O overload and takes several minutes.
   * Network bandwidth overcommitment
-  * Very long garbage collector task for the RegionServer JVM: The ''default garbage collector''
of the HotspotTM JavaTM Virtual Machine runs a ''full gc'' on the ''old space'' when the memory
space is full, which can represent about 90% of the allocated heap space. During this task,
the running program is stopped, the timers as well. If the heap space is mostly in the swap
partition, and moreover if it is larger than the physical memory, the subsequent swap can
yield to I/O overload and takes several minutes.
  === Resolution ===
   * Insure that host name resolution latency is low, or use static entries in /etc/hosts
   * Monitor the network and insure that adequate bandwidth is available for HRPC transactions
@@ -146, +143 @@

   * For Java SE 6, some users have had success with {{{ -XX:+UseConcMarkSweepGC -XX:+CMSIncrementalMode
-XX:ParallelGCThreads=8 }}}.
   * See HBase [[PerformanceTuning|Performance Tuning]] for more on JVM GC tuning.
  
+ 
  <<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. 
@@ -158, +156 @@

   * Use X-Large (c1.xlarge) instances
   * Consider splitting storage and computational function over disjoint instance sets. 
  
+ 
  <<Anchor(9)>>
  == 9. Problem: ZooKeeper SessionExpired events ==
   * Master or RegionServers reinitialize their ZooKeeper wrappers after receiving SessionExpired
events.
@@ -174, +173 @@

  }}}
   * For Java SE 6, some users have had success with {{{ -XX:+UseConcMarkSweepGC -XX:+CMSIncrementalMode
-XX:ParallelGCThreads=8 }}}.  See HBase [[PerformanceTuning|Performance Tuning]] for more
on JVM GC tuning.
  
+ 
  <<Anchor(10)>>
  == 10. Problem: Scanners keep getting timeouts ==
   * Client receives org.apache.hadoop.hbase.UnknownScannerException or timeouts even if the
region server lease is really high. Fixed in HBase 0.20.0
@@ -182, +182 @@

  === Resolution ===
   * Set hbase.client.scanner.caching in hbase-site.xml at a very low value like 1 or use
HTable.setScannerCaching(1).
  
+ 
  <<Anchor(11)>>
  == 11. Problem: Client says no such table but it exists ==
   * Client can't find region in table, says no such table.
@@ -199, +200 @@

  === Resolution ===
   * Use the hostname presented in the error message instead of the value you used. If you
have a DNS server, you can set '''hbase.zookeeper.dns.interface''' and '''hbase.zookeeper.dns.nameserver'''
in hbase-site.xml to make sure it resolves to the correct FQDN.
  
+ 
  <<Anchor(13)>>
- == 13. Problem: Long client pauses under high load; or deadlock if using THBase ==
+ == 13. Problem: Long client pauses under high load; or deadlock if using transactional HBase
(THBase)==
   * Under high load, some client operations take a long time; waiting appears uneven
-  * If using transactional HBase (THBase), apparent deadlocks: for example, in thread dumps
IPC Server handlers are blocked in org.apache.hadoop.hbase.regionserver.tableindexed.IndexedRegion.updateIndex()
+  * If using THBase, apparent deadlocks: for example, in thread dumps IPC Server handlers
are blocked in org.apache.hadoop.hbase.regionserver.tableindexed.IndexedRegion.updateIndex()
  == Causes ==
   * The default number of regionserver RPC handlers is insufficient.
  == Resolution ==
   * Increase the value of "hbase.regionserver.handler.count" in hbase-site.xml. The default
is 10. Try 100.
+ 
  
  <<Anchor(14)>>
  == 14. Problem: Zookeeper does not seem to work on Amazon EC2 ==
@@ -224, +227 @@

  == Resolution ==
   * Use the internal EC2 host names when configuring the Zookeeper quorum peer list. 
  
+ 
  <<Anchor(15)>>
  == 15. Problem: General operating environment issues -- zookeeper session timeouts, regionservers
shutting down, etc ==
  == Causes ==
@@ -231, +235 @@

  == 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 ==
@@ -239, +244 @@

   * 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/current/api/org/apache/hadoop/hbase/client/HTable.html#scannerCaching|HTable.scannerCaching]]
   * This change can be accomplished globally by setting the hbase.client.scanner.caching
property in hbase-site.xml to the desired value.
  
+ 
  <<Anchor(17)>>
  == 17. Problem: My shell or client application throws lots of scary exceptions during normal
operation ==
  == Causes ==

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