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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
can be applied to a Scan instance to return the rows beginning with "row".
<programlisting>
public static final byte[] CF = "cf".getBytes();
public static final byte[] ATTR = "attr".getBytes();
...
HTable htable = ... // instantiate HTable
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.setStopRow( Bytes.toBytes("row" + (char)0)); // stop key is exclusive
ResultScanner rs = htable.getScanner(scan);
@ -389,9 +393,12 @@ try {
<title>Default Get Example</title>
<para>The following Get will only retrieve the current version of the row
<programlisting>
public static final byte[] CF = "cf".getBytes();
public static final byte[] ATTR = "attr".getBytes();
...
Get get = new Get(Bytes.toBytes("row1"));
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>
</para>
</section>
@ -399,11 +406,14 @@ byte[] b = r.getValue(Bytes.toBytes("cf"), Bytes.toBytes("attr")); // returns c
<title>Versioned Get Example</title>
<para>The following Get will return the last 3 versions of the row.
<programlisting>
public static final byte[] CF = "cf".getBytes();
public static final byte[] ATTR = "attr".getBytes();
...
Get get = new Get(Bytes.toBytes("row1"));
get.setMaxVersions(3); // will return last 3 versions of row
Result r = htable.get(get);
byte[] b = r.getValue(Bytes.toBytes("cf"), Bytes.toBytes("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
byte[] b = r.getValue(CF, ATTR); // returns current version of value
List&lt;KeyValue&gt; kv = r.getColumn(CF, ATTR); // returns all versions of this column
</programlisting>
</para>
</section>
@ -425,8 +435,11 @@ List&lt;KeyValue&gt; kv = r.getColumn(Bytes.toBytes("cf"), Bytes.toBytes("attr")
<title>Implicit Version Example</title>
<para>The following Put will be implicitly versioned by HBase with the current time.
<programlisting>
public static final byte[] CF = "cf".getBytes();
public static final byte[] ATTR = "attr".getBytes();
...
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);
</programlisting>
</para>
@ -435,9 +448,12 @@ htable.put(put);
<title>Explicit Version Example</title>
<para>The following Put has the version timestamp explicitly set.
<programlisting>
public static final byte[] CF = "cf".getBytes();
public static final byte[] ATTR = "attr".getBytes();
...
Put put = new Put( Bytes.toBytes(row));
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);
</programlisting>
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.
<programlisting>
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 Text text = new Text();
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...
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>.
<programlisting>
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 {
int i = 0;
@ -1201,7 +1221,7 @@ public static class MyTableReducer extends TableReducer&lt;Text, IntWritable, Im
i += val.get();
}
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);
}