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HBASE-4735 book.xml, schema design keysize code example 

git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1196860 13f79535-47bb-0310-9956-ffa450edef68
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Doug Meil 2011-11-02 23:26:30 +00:00
parent 88643f7220
commit c61f0f296f
1 changed files with 26 additions and 5 deletions
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31
src/docbkx/book.xml
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@ -567,8 +567,8 @@ admin.enableTable(table);
</para>
<section xml:id="number.of.cfs.card"><title>Cardinality of ColumnFamilies</title>
<para>Where multiple ColumnFamilies exist in a single table, be aware of the cardinality (i.e., number of rows).
If ColumnFamily-A has 1000,000 rows and ColumnFamily-B has 1 billion rows, ColumnFamily-A's data will likely be spread
across many, many regions (and RegionServers). This makes mass scans for ColumnFamily-A less efficient.
If ColumnFamilyA has 1000,000 rows and ColumnFamilyB has 1 billion rows, ColumnFamilyA's data will likely be spread
across many, many regions (and RegionServers). This makes mass scans for ColumnFamilyA less efficient.
</para>
</section>
</section>
@ -631,11 +631,32 @@ admin.enableTable(table);
when designing rowkeys.
</para>
</section>
<section xml:id="keysize.example"><title>Numeric Example</title>
<section xml:id="keysize.patterns"><title>Byte Patterns</title>
<para>A long is 8 bytes. You can store an unsigned number up to 18,446,744,073,709,551,615 in those eight bytes.
If you stored this number as a String -- presuming a byte per character -- you need nearly 3x the bytes.
This is a perfect example of a small inefficiency that may not seem like much, but can add up in HBase when
used as rowkeys.
</para>
<para>Not convinced? Below is some sample code that you can run on your own.
<programlisting>
// long
//
long l = 1234567890L;
byte[] lb = Bytes.toBytes(l);
System.out.println("long bytes length: " + lb.length); // returns 8
String s = "" + l;
byte[] sb = Bytes.toBytes(s);
System.out.println("long as string length: " + sb.length); // returns 10
// hash
//
MessageDigest md = MessageDigest.getInstance("MD5");
byte[] digest = md.digest(Bytes.toBytes(s));
System.out.println("md5 digest bytes length: " + digest.length); // returns 16
String sDigest = new String(digest);
byte[] sbDigest = Bytes.toBytes(sDigest);
System.out.println("md5 digest as string length: " + sbDigest.length); // returns 26
</programlisting>
</para>
</section>
</section>