Author: dmeil
Date: Wed Oct 5 16:55:31 2011
New Revision: 1179314
URL: http://svn.apache.org/viewvc?rev=1179314&view=rev
Log:
HBASE-4541 clarifying versions in Schema Design
Modified:
hbase/trunk/src/docbkx/book.xml
Modified: hbase/trunk/src/docbkx/book.xml
URL:
http://svn.apache.org/viewvc/hbase/trunk/src/docbkx/book.xml?rev=1179314&r1=1179313&r2=1179314&view=diff
==============================================================================
--- hbase/trunk/src/docbkx/book.xml (original)
+++ hbase/trunk/src/docbkx/book.xml Wed Oct 5 16:55:31 2011
@@ -445,24 +445,26 @@ admin.enableTable(table);
<title>
Number of Versions
</title>
- <para>The number of row versions to store is configured per column
+ <section 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 is 3.
+ The default for max versions is 3.
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 versions may need to be increased or
decreased depending on application needs.
- </para>
- <para>It is not recommended setting the number of 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>
+ 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>
+ </section>
<section xml:id="schema.minversions">
<title>
Minimum Number of Versions
</title>
- <para>Like number of row versions, the minimum number of row versions to
keep is configured per column
+ <para>Like number of max row versions, the minimum number of row versions
to keep is configured per column
family via <link
xlink:href="http://hbase.apache.org/apidocs/org/apache/hadoop/hbase/HColumnDescriptor.html";>HColumnDescriptor</link>.
- The default is 0, which means the feature is disabled.
+ The default for min versions is 0, which means the feature is disabled.
The minimum number of row versions parameter is used together with the
time-to-live parameter and can be combined with the
number of row versions parameter to allow configurations such as
"keep the last T minutes worth of data, at most N versions,
<emphasis>but keep at least M versions around</emphasis>"
