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From Apache Wiki <wikidi...@apache.org>
Subject [Hadoop Wiki] Trivial Update of "Hbase/HowToMigrate" by stack
Date Tue, 21 Jul 2009 17:46:41 GMT
Dear Wiki user,

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

------------------------------------------------------------------------------
- == Migration in General ==
+ = Migration in General =
  
  In general, performing a HBase migration will consist of the following steps:
  
@@ -12, +12 @@

   * Start the new instance of HBase.
  
  If you would like to learn more about the HBase Migration design, see [http://wiki.apache.org/hadoop/Hbase/Migration
HBase Migration]
+ 
+ Below are general migration notes followed by specifics on how to migrate between particular
versions, newest to oldest.
+ 
+ == Other Migration-Related Concerns ==
+ 
+ Migration is only supported between the file system version of the previous release and
the file system version of the current release. If the existing HBase installation has an
older file system version, it will be necessary to install a HBase release which can perform
the upgrade, run the migration tool and then install the desired release and run its migration
script. (Note that if the existing installation is several versions old, it may be necessary
to repeat this process).
+ 
+ === Redo Logs ===
+ 
+ (Below does not apply if migrating from hbase 0.19 to hbase 0.20)
+ 
+ It is possible that, when running the HBase migration command, the migration will fail because
of "unrecovered redo logs."  Redo logs are generated every time HBase is started, and under
normal circumstances they are removed when HBase is stopped cleanly.  However, if you have
ever stopped HBase in some atypical way (for example, using {{{kill -9}}}), these redo logs
will persist in Hadoop DFS.  To see if you have any unrecovered redo logs, stop any currently-running
instances of HBase and enter: {{{{$HADOOP_HOME}/bin/hadoop dfs -ls /hbase}}}.  All existing
redo logs will be in this directory.  Redo log directories can be removed using dfs {{{-rm}}}
option.  WARNING: redo logs are the only way to recover any data entered before HBase was
improperly stopped.  Removing redo logs with file size greater than zero may result in irreversible
data loss.
  
  == Version-Specific Migration Notes ==
  
@@ -75, +87 @@

  
  Read the new 'Getting Started' carefully before starting up your cluster.  Basic configuration
properties have changed.  For example {{{hbase.master}}}/{{{hbase.master.hostname}}} is no
longer used.  They are replaced by {{{hbase.cluster.distributed}}}.  See the 'Getting Started'
for detail on how to set the new properties.  While your cluster will likely come up on the
old configuration settings, you should move to the new configuration.
  
- === From 0.1.x to 0.2.x or 0.18.x ===
+ == From 0.1.x to 0.2.x or 0.18.x ==
  
  The following are step-by-step instructions for migrating from HBase 0.1 to 0.2 or 0.18.
 Migration from 0.1 to 0.2 requires an upgrade from Hadoop 0.16 to 0.17, and migration from
0.1 to 0.18 requires an upgrade from Hadoop 0.16 to 0.18. The [http://wiki.apache.org/hadoop/Hadoop%20Upgrade
Hadoop Upgrade Instructions] are slightly out-of-date (as of this writing, September 2008).
 As such, the below instructions also clarify the necessary steps for upgrading Hadoop.
  
@@ -93, +105 @@

  
  The API in 0.2 is not backward-compatible with hbase 0.1 versions.  See [http://wiki.apache.org/hadoop/Hbase/Plan-0.2/APIChanges
API Changes] for discussion of the main differences.
  
- == Other Migration-Related Concerns ==
- 
- Migration is only supported between the file system version of the previous release and
the file system version of the current release. If the existing HBase installation has an
older file system version, it will be necessary to install a HBase release which can perform
the upgrade, run the migration tool and then install the desired release and run its migration
script. (Note that if the existing installation is several versions old, it may be necessary
to repeat this process).
- 
- === Redo Logs ===
- 
- It is possible that, when running the HBase migration command, the migration will fail because
of "unrecovered redo logs."  Redo logs are generated every time HBase is started, and under
normal circumstances they are removed when HBase is stopped cleanly.  However, if you have
ever stopped HBase in some atypical way (for example, using {{{kill -9}}}), these redo logs
will persist in Hadoop DFS.  To see if you have any unrecovered redo logs, stop any currently-running
instances of HBase and enter: {{{{$HADOOP_HOME}/bin/hadoop dfs -ls /hbase}}}.  All existing
redo logs will be in this directory.  Redo log directories can be removed using dfs {{{-rm}}}
option.  WARNING: redo logs are the only way to recover any data entered before HBase was
improperly stopped.  Removing redo logs with file size greater than zero may result in irreversible
data loss.
- 

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