Common errors n solutions

Error:
10/12/08 20:10:31 INFO hdfs.DFSClient: Could not obtain block blk_XXXXXXXXXXXXXXXXXXXXXX_YYYYYYYY from any node: java.io.IOException: No live nodes contain current block. Will get new block locations from namenode and retry... ^{[8]
Solution:}
 Make sure you have configured Hadoop's conf/hdfs-site.xml setting the xceivers value to at least the following:

      
        dfs.datanode.max.xcievers
        4096
      
      

Be sure to restart your HDFS after making the above configuration.


Error:

 2010-04-06 03:04:37,542 INFO org.apache.hadoop.hdfs.DFSClient: Exception increateBlockOutputStream java.io.EOFException
 2010-04-06 03:04:37,542 INFO org.apache.hadoop.hdfs.DFSClient: Abandoning block blk_-6935524980745310745_1391901
 

Solution:

Apache HBase is a database. It uses a lot of files all at the same time. The default ulimit -n -- i.e. user file limit -- of 1024 on most *nix systems is insufficient (On mac os x its 256). Any significant amount of loading will lead you to. You may also notice errors such as...

      2010-04-06 03:04:37,542 INFO org.apache.hadoop.hdfs.DFSClient: Exception increateBlockOutputStream java.io.EOFException
      2010-04-06 03:04:37,542 INFO org.apache.hadoop.hdfs.DFSClient: Abandoning block blk_-6935524980745310745_1391901
      

Do yourself a favor and change the upper bound on the number of file descriptors. Set it to north of 10k. The math runs roughly as follows: per ColumnFamily there is at least one StoreFile and possibly up to 5 or 6 if the region is under load. Multiply the average number of StoreFiles per ColumnFamily times the number of regions per RegionServer. For example, assuming that a schema had 3 ColumnFamilies per region with an average of 3 StoreFiles per ColumnFamily, and there are 100 regions per RegionServer, the JVM will open 3 * 3 * 100 = 900 file descriptors (not counting open jar files, config files, etc.)
You should also up the hbase users' nproc setting; under load, a low-nproc setting could manifest as OutOfMemoryError
To be clear, upping the file descriptors and nproc for the user who is running the HBase process is an operating system configuration, not an HBase configuration. Also, a common mistake is that administrators will up the file descriptors for a particular user but for whatever reason, HBase will be running as some one else. HBase prints in its logs as the first line the ulimit its seeing. Ensure its correct.

UserPriviledgedAction:Give chown rights to hduser
session 0*0 for server null :network issue
Clock sync error:set same time in master n all slaves to synchronise the clocks
Unable to read additional data from clientsessionid:Error comes when slaves are removed and data is not replicated properly.Add the slaves back to recover data.


If you are on Ubuntu you will need to make the following changes:
In the file /etc/security/limits.conf add a line like:

hadoop  -       nofile  32768

Replace hadoop with whatever user is running Hadoop and HBase. If you have separate users, you will need 2 entries, one for each user. In the same file set nproc hard and soft limits. For example:

hadoop soft/hard nproc 32000

.
In the file /etc/pam.d/common-session add as the last line in the file:

session required  pam_limits.so

Otherwise the changes in /etc/security/limits.conf won't be applied.
Don't forget to log out and back in again for the changes to take effect!



HBase will lose data unless it is running on an HDFS that has a durable sync implementation. DO NOT use Hadoop 0.20.2, Hadoop 0.20.203.0, and Hadoop 0.20.204.0 which DO NOT have this attribute. Currently only Hadoop versions 0.20.205.x or any release in excess of this version -- this includes hadoop-1.0.0 -- have a working, durable sync ^[7]. Sync has to be explicitly enabled by setting dfs.support.append equal to true on both the client side -- in hbase-site.xml -- and on the serverside in hdfs-site.xml (The sync facility HBase needs is a subset of the append code path).

  
    dfs.support.append
    true
  
        

 ^{add to hbase-site}


 
  hbase.regionserver.class
        org.apache.hadoop.hbase.ipc.IndexedRegionInterface
            This configuration is required to enable indexing on
            hbase and to be able to create secondary indexes
           

       

       
            hbase.regionserver.impl
           
            org.apache.hadoop.hbase.regionserver.tableindexed.IndexedRegionServer
           
            This configuration is required to enable indexing on
            hbase and to be able to create secondary indexes