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HBASE-11154 Document how to use Reverse Scan API (Misty Stanley-Jones) 

git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1594371 13f79535-47bb-0310-9956-ffa450edef68
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Michael Stack 2014-05-13 20:30:00 +00:00
parent 76322859a4
commit 5102668714
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src/main/docbkx/schema_design.xml
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@ -199,6 +199,13 @@ COLUMN CELL
</section> </section>
<section xml:id="reverse.timestamp"><title>Reverse Timestamps</title> <section xml:id="reverse.timestamp"><title>Reverse Timestamps</title>
<note>
<title>Reverse Scan API</title>
<para>
<link xlink:href="https://issues.apache.org/jira/browse/HBASE-4811">HBASE-4811</link> implements an API to scan a table or a range within a table in reverse, reducing the need to optimize your schema for forward or reverse scanning. This feature is available in HBase 0.98 and later. See <link xlink:href="https://hbase.apache.org/apidocs/org/apache/hadoop/hbase/client/Scan.html#setReversed%28boolean" /> for more information.
</para>
</note>
<para>A common problem in database processing is quickly finding the most recent version of a value. A technique using reverse timestamps <para>A common problem in database processing is quickly finding the most recent version of a value. A technique using reverse timestamps
as a part of the key can help greatly with a special case of this problem. Also found in the HBase chapter of Tom White's book Hadoop: The Definitive Guide (O'Reilly), as a part of the key can help greatly with a special case of this problem. Also found in the HBase chapter of Tom White's book Hadoop: The Definitive Guide (O'Reilly),
the technique involves appending (<code>Long.MAX_VALUE - timestamp</code>) to the end of any key, e.g., [key][reverse_timestamp]. the technique involves appending (<code>Long.MAX_VALUE - timestamp</code>) to the end of any key, e.g., [key][reverse_timestamp].
@ -224,7 +231,7 @@ COLUMN CELL
<section xml:id="rowkey.regionsplits"><title>Relationship Between RowKeys and Region Splits</title> <section xml:id="rowkey.regionsplits"><title>Relationship Between RowKeys and Region Splits</title>
<para>If you pre-split your table, it is <emphasis>critical</emphasis> to understand how your rowkey will be distributed across <para>If you pre-split your table, it is <emphasis>critical</emphasis> to understand how your rowkey will be distributed across
the region boundaries. As an example of why this is important, consider the example of using displayable hex characters as the the region boundaries. As an example of why this is important, consider the example of using displayable hex characters as the
lead position of the key (e.g., ""0000000000000000" to "ffffffffffffffff"). Running those key ranges through <code>Bytes.split</code> lead position of the key (e.g., &quot;0000000000000000&quot; to &quot;ffffffffffffffff&quot;). Running those key ranges through <code>Bytes.split</code>
(which is the split strategy used when creating regions in <code>HBaseAdmin.createTable(byte[] startKey, byte[] endKey, numRegions)</code> (which is the split strategy used when creating regions in <code>HBaseAdmin.createTable(byte[] startKey, byte[] endKey, numRegions)</code>
for 10 regions will generate the following splits... for 10 regions will generate the following splits...
</para> </para>
@ -504,6 +511,12 @@ long bucket = timestamp % numBuckets;
</para> </para>
<para>Neither approach is wrong, it just depends on what is most appropriate for the situation. <para>Neither approach is wrong, it just depends on what is most appropriate for the situation.
</para> </para>
<note>
<title>Reverse Scan API</title>
<para>
<link xlink:href="https://issues.apache.org/jira/browse/HBASE-4811">HBASE-4811</link> implements an API to scan a table or a range within a table in reverse, reducing the need to optimize your schema for forward or reverse scanning. This feature is available in HBase 0.98 and later. See <link xlink:href="https://hbase.apache.org/apidocs/org/apache/hadoop/hbase/client/Scan.html#setReversed%28boolean" /> for more information.
</para>
</note>
</section> <!-- revts --> </section> <!-- revts -->
<section xml:id="schema.casestudies.log-timeseries.varkeys"> <section xml:id="schema.casestudies.log-timeseries.varkeys">
<title>Variangle Length or Fixed Length Rowkeys?</title> <title>Variangle Length or Fixed Length Rowkeys?</title>