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hbase-8182. book.xml. Updating refGuide to use byte-array constants (setting good example). 

git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1459939 13f79535-47bb-0310-9956-ffa450edef68
This commit is contained in:
Doug Meil 2013-03-22 19:23:15 +00:00
parent 423f0742e3
commit c36d3069e4
1 changed files with 28 additions and 8 deletions
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36
src/docbkx/book.xml
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@ -261,10 +261,14 @@
and then another set of rows with the keys "abc1", "abc2", and "abc3". The following example shows how startRow and stopRow and then another set of rows with the keys "abc1", "abc2", and "abc3". The following example shows how startRow and stopRow
can be applied to a Scan instance to return the rows beginning with "row". can be applied to a Scan instance to return the rows beginning with "row".
<programlisting> <programlisting>
public static final byte[] CF = "cf".getBytes();
public static final byte[] ATTR = "attr".getBytes();
...
HTable htable = ... // instantiate HTable HTable htable = ... // instantiate HTable
Scan scan = new Scan(); Scan scan = new Scan();
scan.addColumn(Bytes.toBytes("cf"),Bytes.toBytes("attr")); scan.addColumn(CF, ATTR);
scan.setStartRow( Bytes.toBytes("row")); // start key is inclusive scan.setStartRow( Bytes.toBytes("row")); // start key is inclusive
scan.setStopRow( Bytes.toBytes("row" + (char)0)); // stop key is exclusive scan.setStopRow( Bytes.toBytes("row" + (char)0)); // stop key is exclusive
ResultScanner rs = htable.getScanner(scan); ResultScanner rs = htable.getScanner(scan);
@ -389,9 +393,12 @@ try {
<title>Default Get Example</title> <title>Default Get Example</title>
<para>The following Get will only retrieve the current version of the row <para>The following Get will only retrieve the current version of the row
<programlisting> <programlisting>
public static final byte[] CF = "cf".getBytes();
public static final byte[] ATTR = "attr".getBytes();
...
Get get = new Get(Bytes.toBytes("row1")); Get get = new Get(Bytes.toBytes("row1"));
Result r = htable.get(get); Result r = htable.get(get);
byte[] b = r.getValue(Bytes.toBytes("cf"), Bytes.toBytes("attr")); // returns current version of value byte[] b = r.getValue(CF, ATTR); // returns current version of value
</programlisting> </programlisting>
</para> </para>
</section> </section>
@ -399,11 +406,14 @@ byte[] b = r.getValue(Bytes.toBytes("cf"), Bytes.toBytes("attr")); // returns c
<title>Versioned Get Example</title> <title>Versioned Get Example</title>
<para>The following Get will return the last 3 versions of the row. <para>The following Get will return the last 3 versions of the row.
<programlisting> <programlisting>
public static final byte[] CF = "cf".getBytes();
public static final byte[] ATTR = "attr".getBytes();
...
Get get = new Get(Bytes.toBytes("row1")); Get get = new Get(Bytes.toBytes("row1"));
get.setMaxVersions(3); // will return last 3 versions of row get.setMaxVersions(3); // will return last 3 versions of row
Result r = htable.get(get); Result r = htable.get(get);
byte[] b = r.getValue(Bytes.toBytes("cf"), Bytes.toBytes("attr")); // returns current version of value byte[] b = r.getValue(CF, ATTR); // returns current version of value
List&lt;KeyValue&gt; kv = r.getColumn(Bytes.toBytes("cf"), Bytes.toBytes("attr")); // returns all versions of this column List&lt;KeyValue&gt; kv = r.getColumn(CF, ATTR); // returns all versions of this column
</programlisting> </programlisting>
</para> </para>
</section> </section>
@ -425,8 +435,11 @@ List&lt;KeyValue&gt; kv = r.getColumn(Bytes.toBytes("cf"), Bytes.toBytes("attr")
<title>Implicit Version Example</title> <title>Implicit Version Example</title>
<para>The following Put will be implicitly versioned by HBase with the current time. <para>The following Put will be implicitly versioned by HBase with the current time.
<programlisting> <programlisting>
public static final byte[] CF = "cf".getBytes();
public static final byte[] ATTR = "attr".getBytes();
...
Put put = new Put(Bytes.toBytes(row)); Put put = new Put(Bytes.toBytes(row));
put.add(Bytes.toBytes("cf"), Bytes.toBytes("attr1"), Bytes.toBytes( data)); put.add(CF, ATTR, Bytes.toBytes( data));
htable.put(put); htable.put(put);
</programlisting> </programlisting>
</para> </para>
@ -435,9 +448,12 @@ htable.put(put);
<title>Explicit Version Example</title> <title>Explicit Version Example</title>
<para>The following Put has the version timestamp explicitly set. <para>The following Put has the version timestamp explicitly set.
<programlisting> <programlisting>
public static final byte[] CF = "cf".getBytes();
public static final byte[] ATTR = "attr".getBytes();
...
Put put = new Put( Bytes.toBytes(row)); Put put = new Put( Bytes.toBytes(row));
long explicitTimeInMs = 555; // just an example long explicitTimeInMs = 555; // just an example
put.add(Bytes.toBytes("cf"), Bytes.toBytes("attr1"), explicitTimeInMs, Bytes.toBytes(data)); put.add(CF, ATTR, explicitTimeInMs, Bytes.toBytes(data));
htable.put(put); htable.put(put);
</programlisting> </programlisting>
Caution: the version timestamp is internally by HBase for things like time-to-live calculations. Caution: the version timestamp is internally by HBase for things like time-to-live calculations.
@ -1179,12 +1195,14 @@ if (!b) {
This value is used as the key to emit from the mapper, and an <classname>IntWritable</classname> represents an instance counter. This value is used as the key to emit from the mapper, and an <classname>IntWritable</classname> represents an instance counter.
<programlisting> <programlisting>
public static class MyMapper extends TableMapper&lt;Text, IntWritable&gt; { public static class MyMapper extends TableMapper&lt;Text, IntWritable&gt; {
public static final byte[] CF = "cf".getBytes();
public static final byte[] ATTR1 = "attr1".getBytes();
private final IntWritable ONE = new IntWritable(1); private final IntWritable ONE = new IntWritable(1);
private Text text = new Text(); private Text text = new Text();
public void map(ImmutableBytesWritable row, Result value, Context context) throws IOException, InterruptedException { public void map(ImmutableBytesWritable row, Result value, Context context) throws IOException, InterruptedException {
String val = new String(value.getValue(Bytes.toBytes("cf"), Bytes.toBytes("attr1"))); String val = new String(value.getValue(CF, ATTR1));
text.set(val); // we can only emit Writables... text.set(val); // we can only emit Writables...
context.write(text, ONE); context.write(text, ONE);
@ -1194,6 +1212,8 @@ public static class MyMapper extends TableMapper&lt;Text, IntWritable&gt; {
In the reducer, the "ones" are counted (just like any other MR example that does this), and then emits a <classname>Put</classname>. In the reducer, the "ones" are counted (just like any other MR example that does this), and then emits a <classname>Put</classname>.
<programlisting> <programlisting>
public static class MyTableReducer extends TableReducer&lt;Text, IntWritable, ImmutableBytesWritable&gt; { public static class MyTableReducer extends TableReducer&lt;Text, IntWritable, ImmutableBytesWritable&gt; {
public static final byte[] CF = "cf".getBytes();
public static final byte[] COUNT = "count".getBytes();
public void reduce(Text key, Iterable&lt;IntWritable&gt; values, Context context) throws IOException, InterruptedException { public void reduce(Text key, Iterable&lt;IntWritable&gt; values, Context context) throws IOException, InterruptedException {
int i = 0; int i = 0;
@ -1201,7 +1221,7 @@ public static class MyTableReducer extends TableReducer&lt;Text, IntWritable, Im
i += val.get(); i += val.get();
} }
Put put = new Put(Bytes.toBytes(key.toString())); Put put = new Put(Bytes.toBytes(key.toString()));
put.add(Bytes.toBytes("cf"), Bytes.toBytes("count"), Bytes.toBytes(i)); put.add(CF, COUNT, Bytes.toBytes(i));
context.write(null, put); context.write(null, put);
} }