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From: Apache Wiki <wikidiffs@apache.org>
To: core-commits@hadoop.apache.org
Date: Fri, 22 May 2009 05:36:20 -0000
Message-ID: <20090522053620.11869.41466@eos.apache.org>
Subject: [Hadoop Wiki] Update of "Hbase/RollingRestart" by stack

Dear Wiki user,

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

New page:
If you want to upgrade between point versions -- e.g. from 0.20.0 to 0.20.1 -- of HBase or change configurations WITHOUT bringing down your whole cluster -- i.e. you want to keep serving through the upgrade -- follow the below '''Rolling Restart''' receipe. This feature is available in 0.20.0 HBase (Unreleased as of the writing of this page).

In the below, you will take down one or more servers at a time, upgrade or change their configuration, and then bring the servers back on line afterward.  Ideally, you'd do the upgrade a server-at-a-time to minimize region churn but if your cluster large, you can upgrade a few on each iteration. Just be sure that the number of servers you drop is not of a proportion as to render your serving cluster a mortal blow.

Per regionserver, first update the pertinent jar or configuration.  Next, run the following to stop the server: {{{$ ${HBASE_HOME}/bin/hbase-daemon.sh stop regionserver}}}.  Wait until the server comes to a complete stop.  Then  restart it by doing the following: {{{$ ${HBASE_HOME}/bin/hbase-daemon.sh start regionserver}}}. 

For the master, you'll need to kill it.  If you do {{{./bin/hbase-daemon.sh stop master}}}, it'll stop the whole cluster.   Make sure the master is not in the midst of handling a regionserver crash splitting logs.  Otherwise, killing its should be safe.  Once its dead, start it up again with: {{{$ ${HBASE_HOME}/bin/hbase-daemon.sh start master}}}.

The above currently will not work for minor upgrades where data migration may be required or where RPC version numbers have changed.