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HBASE-11784 Document global configuration for maxVersion

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Misty Stanley-Jones 2014-09-16 13:04:28 +10:00
parent 1f1a2c514e
commit d93b5ce04f
2 changed files with 39 additions and 3 deletions
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31
src/main/docbkx/book.xml
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@ -652,6 +652,37 @@ try {
<emphasis>Overwriting values at existing timestamps</emphasis> mentioned in the
article no longer holds in HBase. This section is basically a synopsis of this article
by Bruno Dumon.</para>
<section xml:id="specify.number.of.versions">
<title>Specifying the Number of Versions to Store</title>
<para>The maximum number of versions to store for a given column is part of the column
schema and is specified at table creation, or via an <command>alter</command> command, via
<code>HColumnDescriptor.DEFAULT_VERSIONS</code>. Prior to HBase 0.96, the default number
of versions kept was <literal>3</literal>, but in 0.96 and newer has been changed to
<literal>1</literal>.</para>
<example>
<title>Modify the Maximum Number of Versions for a Column</title>
<para>This example uses HBase Shell to keep a maximum of 5 versions of column
<code>f1</code>. You could also use <link
xlink:href="http://hbase.apache.org/apidocs/org/apache/hadoop/hbase/HColumnDescriptor.html"
>HColumnDescriptor</link>.</para>
<screen><![CDATA[hbase> alter ‘t1′, NAME => ‘f1′, VERSIONS => 5]]></screen>
</example>
<example>
<title>Modify the Minimum Number of Versions for a Column</title>
<para>You can also specify the minimum number of versions to store. By default, this is
set to 0, which means the feature is disabled. The following example sets the minimum
number of versions on field <code>f1</code> to <literal>2</literal>, via HBase Shell.
You could also use <link
xlink:href="http://hbase.apache.org/apidocs/org/apache/hadoop/hbase/HColumnDescriptor.html"
>HColumnDescriptor</link>.</para>
<screen><![CDATA[hbase> alter ‘t1′, NAME => ‘f1′, MIN_VERSIONS => 2]]></screen>
</example>
<para>Starting with HBase 0.98.2, you can specify a global default for the maximum number of
versions kept for all newly-created columns, by setting
<option>hbase.column.max.version</option> in <filename>hbase-site.xml</filename>. See
<xref linkend="hbase.column.max.version"/>.</para>
</section>
<section
xml:id="versions.ops">

11
src/main/docbkx/schema_design.xml
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@ -439,15 +439,18 @@ public static byte[][] getHexSplits(String startKey, String endKey, int numRegio
xml:id="schema.versions.max">
<title>Maximum Number of Versions</title>
<para>The maximum number of row versions to store is configured per column family via <link
xlink:href="http://hbase.apache.org/apidocs/org/apache/hadoop/hbase/HColumnDescriptor.html">HColumnDescriptor</link>.
The default for max versions is 1. This is an important parameter because as described in <xref
linkend="datamodel" /> section HBase does <emphasis>not</emphasis> overwrite row values,
xlink:href="http://hbase.apache.org/apidocs/org/apache/hadoop/hbase/HColumnDescriptor.html"
>HColumnDescriptor</link>. The default for max versions is 3 prior to HBase 0.96.x, and 1
in newer versions. This is an important parameter because as described in <xref
linkend="datamodel"/> section HBase does <emphasis>not</emphasis> overwrite row values,
but rather stores different values per row by time (and qualifier). Excess versions are
removed during major compactions. The number of max versions may need to be increased or
decreased depending on application needs. </para>
<para>It is not recommended setting the number of max versions to an exceedingly high level
(e.g., hundreds or more) unless those old values are very dear to you because this will
greatly increase StoreFile size. </para>
<para>See <xref linkend="specify.number.of.versions"/> for examples for setting the maximum
number of versions on a given column or globally.</para>
</section>
<section
xml:id="schema.minversions">
@ -462,6 +465,8 @@ public static byte[][] getHexSplits(String startKey, String endKey, int numRegio
around</emphasis>" (where M is the value for minimum number of row versions, M&lt;N). This
parameter should only be set when time-to-live is enabled for a column family and must be
less than the number of row versions. </para>
<para>See <xref linkend="specify.number.of.versions"/> for examples for setting the minimum
number of versions on a given column.</para>
</section>
</section>
<section