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| 82 | <H2> |
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| 83 | Package org.apache.hadoop.mapred.join |
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| 84 | </H2> |
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| 85 | Given a set of sorted datasets keyed with the same class and yielding equal |
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| 86 | partitions, it is possible to effect a join of those datasets prior to the map. |
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| 87 | <P> |
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| 88 | <B>See:</B> |
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| 89 | <BR> |
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| 90 | <A HREF="#package_description"><B>Description</B></A> |
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| 91 | <P> |
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| 92 | |
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| 93 | <TABLE BORDER="1" WIDTH="100%" CELLPADDING="3" CELLSPACING="0" SUMMARY=""> |
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| 95 | <TH ALIGN="left" COLSPAN="2"><FONT SIZE="+2"> |
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| 96 | <B>Interface Summary</B></FONT></TH> |
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| 97 | </TR> |
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| 98 | <TR BGCOLOR="white" CLASS="TableRowColor"> |
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| 99 | <TD WIDTH="15%"><B><A HREF="../../../../../org/apache/hadoop/mapred/join/ComposableInputFormat.html" title="interface in org.apache.hadoop.mapred.join">ComposableInputFormat<K extends WritableComparable,V extends Writable></A></B></TD> |
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| 100 | <TD>Refinement of InputFormat requiring implementors to provide |
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| 101 | ComposableRecordReader instead of RecordReader.</TD> |
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| 102 | </TR> |
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| 103 | <TR BGCOLOR="white" CLASS="TableRowColor"> |
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| 104 | <TD WIDTH="15%"><B><A HREF="../../../../../org/apache/hadoop/mapred/join/ComposableRecordReader.html" title="interface in org.apache.hadoop.mapred.join">ComposableRecordReader<K extends WritableComparable,V extends Writable></A></B></TD> |
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| 105 | <TD>Additional operations required of a RecordReader to participate in a join.</TD> |
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| 106 | </TR> |
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| 107 | <TR BGCOLOR="white" CLASS="TableRowColor"> |
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| 108 | <TD WIDTH="15%"><B><A HREF="../../../../../org/apache/hadoop/mapred/join/ResetableIterator.html" title="interface in org.apache.hadoop.mapred.join">ResetableIterator<T extends Writable></A></B></TD> |
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| 109 | <TD>This defines an interface to a stateful Iterator that can replay elements |
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| 110 | added to it directly.</TD> |
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| 111 | </TR> |
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| 112 | </TABLE> |
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| 113 | |
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| 114 | |
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| 115 | <P> |
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| 116 | |
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| 119 | <TH ALIGN="left" COLSPAN="2"><FONT SIZE="+2"> |
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| 120 | <B>Class Summary</B></FONT></TH> |
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| 121 | </TR> |
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| 122 | <TR BGCOLOR="white" CLASS="TableRowColor"> |
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| 123 | <TD WIDTH="15%"><B><A HREF="../../../../../org/apache/hadoop/mapred/join/ArrayListBackedIterator.html" title="class in org.apache.hadoop.mapred.join">ArrayListBackedIterator<X extends Writable></A></B></TD> |
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| 124 | <TD>This class provides an implementation of ResetableIterator.</TD> |
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| 125 | </TR> |
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| 126 | <TR BGCOLOR="white" CLASS="TableRowColor"> |
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| 127 | <TD WIDTH="15%"><B><A HREF="../../../../../org/apache/hadoop/mapred/join/CompositeInputFormat.html" title="class in org.apache.hadoop.mapred.join">CompositeInputFormat<K extends WritableComparable></A></B></TD> |
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| 128 | <TD>An InputFormat capable of performing joins over a set of data sources sorted |
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| 129 | and partitioned the same way.</TD> |
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| 130 | </TR> |
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| 131 | <TR BGCOLOR="white" CLASS="TableRowColor"> |
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| 132 | <TD WIDTH="15%"><B><A HREF="../../../../../org/apache/hadoop/mapred/join/CompositeInputSplit.html" title="class in org.apache.hadoop.mapred.join">CompositeInputSplit</A></B></TD> |
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| 133 | <TD>This InputSplit contains a set of child InputSplits.</TD> |
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| 134 | </TR> |
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| 135 | <TR BGCOLOR="white" CLASS="TableRowColor"> |
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| 136 | <TD WIDTH="15%"><B><A HREF="../../../../../org/apache/hadoop/mapred/join/CompositeRecordReader.html" title="class in org.apache.hadoop.mapred.join">CompositeRecordReader<K extends WritableComparable,V extends Writable,X extends Writable></A></B></TD> |
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| 137 | <TD>A RecordReader that can effect joins of RecordReaders sharing a common key |
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| 138 | type and partitioning.</TD> |
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| 139 | </TR> |
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| 140 | <TR BGCOLOR="white" CLASS="TableRowColor"> |
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| 141 | <TD WIDTH="15%"><B><A HREF="../../../../../org/apache/hadoop/mapred/join/InnerJoinRecordReader.html" title="class in org.apache.hadoop.mapred.join">InnerJoinRecordReader<K extends WritableComparable></A></B></TD> |
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| 142 | <TD>Full inner join.</TD> |
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| 143 | </TR> |
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| 144 | <TR BGCOLOR="white" CLASS="TableRowColor"> |
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| 145 | <TD WIDTH="15%"><B><A HREF="../../../../../org/apache/hadoop/mapred/join/JoinRecordReader.html" title="class in org.apache.hadoop.mapred.join">JoinRecordReader<K extends WritableComparable></A></B></TD> |
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| 146 | <TD>Base class for Composite joins returning Tuples of arbitrary Writables.</TD> |
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| 147 | </TR> |
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| 148 | <TR BGCOLOR="white" CLASS="TableRowColor"> |
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| 149 | <TD WIDTH="15%"><B><A HREF="../../../../../org/apache/hadoop/mapred/join/MultiFilterRecordReader.html" title="class in org.apache.hadoop.mapred.join">MultiFilterRecordReader<K extends WritableComparable,V extends Writable></A></B></TD> |
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| 150 | <TD>Base class for Composite join returning values derived from multiple |
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| 151 | sources, but generally not tuples.</TD> |
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| 152 | </TR> |
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| 153 | <TR BGCOLOR="white" CLASS="TableRowColor"> |
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| 154 | <TD WIDTH="15%"><B><A HREF="../../../../../org/apache/hadoop/mapred/join/OuterJoinRecordReader.html" title="class in org.apache.hadoop.mapred.join">OuterJoinRecordReader<K extends WritableComparable></A></B></TD> |
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| 155 | <TD>Full outer join.</TD> |
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| 156 | </TR> |
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| 157 | <TR BGCOLOR="white" CLASS="TableRowColor"> |
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| 158 | <TD WIDTH="15%"><B><A HREF="../../../../../org/apache/hadoop/mapred/join/OverrideRecordReader.html" title="class in org.apache.hadoop.mapred.join">OverrideRecordReader<K extends WritableComparable,V extends Writable></A></B></TD> |
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| 159 | <TD>Prefer the "rightmost" data source for this key.</TD> |
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| 160 | </TR> |
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| 161 | <TR BGCOLOR="white" CLASS="TableRowColor"> |
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| 162 | <TD WIDTH="15%"><B><A HREF="../../../../../org/apache/hadoop/mapred/join/Parser.html" title="class in org.apache.hadoop.mapred.join">Parser</A></B></TD> |
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| 163 | <TD>Very simple shift-reduce parser for join expressions.</TD> |
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| 164 | </TR> |
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| 165 | <TR BGCOLOR="white" CLASS="TableRowColor"> |
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| 166 | <TD WIDTH="15%"><B><A HREF="../../../../../org/apache/hadoop/mapred/join/Parser.Node.html" title="class in org.apache.hadoop.mapred.join">Parser.Node</A></B></TD> |
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| 167 | <TD> </TD> |
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| 168 | </TR> |
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| 169 | <TR BGCOLOR="white" CLASS="TableRowColor"> |
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| 170 | <TD WIDTH="15%"><B><A HREF="../../../../../org/apache/hadoop/mapred/join/Parser.NodeToken.html" title="class in org.apache.hadoop.mapred.join">Parser.NodeToken</A></B></TD> |
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| 171 | <TD> </TD> |
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| 172 | </TR> |
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| 173 | <TR BGCOLOR="white" CLASS="TableRowColor"> |
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| 174 | <TD WIDTH="15%"><B><A HREF="../../../../../org/apache/hadoop/mapred/join/Parser.NumToken.html" title="class in org.apache.hadoop.mapred.join">Parser.NumToken</A></B></TD> |
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| 175 | <TD> </TD> |
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| 176 | </TR> |
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| 177 | <TR BGCOLOR="white" CLASS="TableRowColor"> |
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| 178 | <TD WIDTH="15%"><B><A HREF="../../../../../org/apache/hadoop/mapred/join/Parser.StrToken.html" title="class in org.apache.hadoop.mapred.join">Parser.StrToken</A></B></TD> |
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| 179 | <TD> </TD> |
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| 180 | </TR> |
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| 181 | <TR BGCOLOR="white" CLASS="TableRowColor"> |
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| 182 | <TD WIDTH="15%"><B><A HREF="../../../../../org/apache/hadoop/mapred/join/Parser.Token.html" title="class in org.apache.hadoop.mapred.join">Parser.Token</A></B></TD> |
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| 183 | <TD>Tagged-union type for tokens from the join expression.</TD> |
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| 184 | </TR> |
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| 185 | <TR BGCOLOR="white" CLASS="TableRowColor"> |
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| 186 | <TD WIDTH="15%"><B><A HREF="../../../../../org/apache/hadoop/mapred/join/ResetableIterator.EMPTY.html" title="class in org.apache.hadoop.mapred.join">ResetableIterator.EMPTY<U extends Writable></A></B></TD> |
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| 187 | <TD> </TD> |
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| 188 | </TR> |
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| 189 | <TR BGCOLOR="white" CLASS="TableRowColor"> |
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| 190 | <TD WIDTH="15%"><B><A HREF="../../../../../org/apache/hadoop/mapred/join/StreamBackedIterator.html" title="class in org.apache.hadoop.mapred.join">StreamBackedIterator<X extends Writable></A></B></TD> |
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| 191 | <TD>This class provides an implementation of ResetableIterator.</TD> |
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| 192 | </TR> |
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| 193 | <TR BGCOLOR="white" CLASS="TableRowColor"> |
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| 194 | <TD WIDTH="15%"><B><A HREF="../../../../../org/apache/hadoop/mapred/join/TupleWritable.html" title="class in org.apache.hadoop.mapred.join">TupleWritable</A></B></TD> |
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| 195 | <TD>Writable type storing multiple <A HREF="../../../../../org/apache/hadoop/io/Writable.html" title="interface in org.apache.hadoop.io"><CODE>Writable</CODE></A>s.</TD> |
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| 196 | </TR> |
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| 197 | <TR BGCOLOR="white" CLASS="TableRowColor"> |
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| 198 | <TD WIDTH="15%"><B><A HREF="../../../../../org/apache/hadoop/mapred/join/WrappedRecordReader.html" title="class in org.apache.hadoop.mapred.join">WrappedRecordReader<K extends WritableComparable,U extends Writable></A></B></TD> |
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| 199 | <TD>Proxy class for a RecordReader participating in the join framework.</TD> |
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| 200 | </TR> |
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| 201 | </TABLE> |
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| 202 | |
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| 203 | |
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| 204 | <P> |
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| 205 | |
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| 206 | <TABLE BORDER="1" WIDTH="100%" CELLPADDING="3" CELLSPACING="0" SUMMARY=""> |
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| 207 | <TR BGCOLOR="#CCCCFF" CLASS="TableHeadingColor"> |
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| 208 | <TH ALIGN="left" COLSPAN="2"><FONT SIZE="+2"> |
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| 209 | <B>Enum Summary</B></FONT></TH> |
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| 210 | </TR> |
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| 211 | <TR BGCOLOR="white" CLASS="TableRowColor"> |
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| 212 | <TD WIDTH="15%"><B><A HREF="../../../../../org/apache/hadoop/mapred/join/Parser.TType.html" title="enum in org.apache.hadoop.mapred.join">Parser.TType</A></B></TD> |
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| 213 | <TD> </TD> |
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| 214 | </TR> |
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| 215 | </TABLE> |
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| 216 | |
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| 217 | |
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| 218 | <P> |
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| 219 | <A NAME="package_description"><!-- --></A><H2> |
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| 220 | Package org.apache.hadoop.mapred.join Description |
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| 221 | </H2> |
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| 222 | |
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| 223 | <P> |
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| 224 | <p>Given a set of sorted datasets keyed with the same class and yielding equal |
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| 225 | partitions, it is possible to effect a join of those datasets prior to the map. |
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| 226 | This could save costs in re-partitioning, sorting, shuffling, and writing out |
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| 227 | data required in the general case.</p> |
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| 228 | |
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| 229 | <h3><a name="Interface"></a>Interface</h3> |
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| 230 | |
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| 231 | <p>The attached code offers the following interface to users of these |
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| 232 | classes.</p> |
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| 233 | |
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| 234 | <table> |
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| 235 | <tr><th>property</th><th>required</th><th>value</th></tr> |
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| 236 | <tr><td>mapred.join.expr</td><td>yes</td> |
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| 237 | <td>Join expression to effect over input data</td></tr> |
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| 238 | <tr><td>mapred.join.keycomparator</td><td>no</td> |
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| 239 | <td><tt>WritableComparator</tt> class to use for comparing keys</td></tr> |
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| 240 | <tr><td>mapred.join.define.<ident></td><td>no</td> |
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| 241 | <td>Class mapped to identifier in join expression</td></tr> |
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| 242 | </table> |
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| 243 | |
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| 244 | <p>The join expression understands the following grammar:</p> |
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| 245 | |
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| 246 | <pre>func ::= <ident>([<func>,]*<func>) |
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| 247 | func ::= tbl(<class>,"<path>"); |
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| 248 | |
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| 249 | </pre> |
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| 250 | |
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| 251 | <p>Operations included in this patch are partitioned into one of two types: |
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| 252 | join operations emitting tuples and "multi-filter" operations emitting a |
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| 253 | single value from (but not necessarily included in) a set of input values. |
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| 254 | For a given key, each operation will consider the cross product of all |
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| 255 | values for all sources at that node.</p> |
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| 256 | |
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| 257 | <p>Identifiers supported by default:</p> |
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| 258 | |
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| 259 | <table> |
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| 260 | <tr><th>identifier</th><th>type</th><th>description</th></tr> |
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| 261 | <tr><td>inner</td><td>Join</td><td>Full inner join</td></tr> |
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| 262 | <tr><td>outer</td><td>Join</td><td>Full outer join</td></tr> |
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| 263 | <tr><td>override</td><td>MultiFilter</td> |
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| 264 | <td>For a given key, prefer values from the rightmost source</td></tr> |
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| 265 | </table> |
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| 266 | |
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| 267 | <p>A user of this class must set the <tt>InputFormat</tt> for the job to |
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| 268 | <tt>CompositeInputFormat</tt> and define a join expression accepted by the |
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| 269 | preceding grammar. For example, both of the following are acceptable:</p> |
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| 270 | |
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| 271 | <pre>inner(tbl(org.apache.hadoop.mapred.SequenceFileInputFormat.class, |
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| 272 | "hdfs://host:8020/foo/bar"), |
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| 273 | tbl(org.apache.hadoop.mapred.SequenceFileInputFormat.class, |
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| 274 | "hdfs://host:8020/foo/baz")) |
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| 275 | |
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| 276 | outer(override(tbl(org.apache.hadoop.mapred.SequenceFileInputFormat.class, |
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| 277 | "hdfs://host:8020/foo/bar"), |
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| 278 | tbl(org.apache.hadoop.mapred.SequenceFileInputFormat.class, |
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| 279 | "hdfs://host:8020/foo/baz")), |
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| 280 | tbl(org.apache.hadoop.mapred/SequenceFileInputFormat.class, |
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| 281 | "hdfs://host:8020/foo/rab")) |
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| 282 | </pre> |
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| 283 | |
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| 284 | <p><tt>CompositeInputFormat</tt> includes a handful of convenience methods to |
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| 285 | aid construction of these verbose statements.</p> |
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| 286 | |
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| 287 | <p>As in the second example, joins may be nested. Users may provide a |
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| 288 | comparator class in the <tt>mapred.join.keycomparator</tt> property to specify |
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| 289 | the ordering of their keys, or accept the default comparator as returned by |
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| 290 | <tt>WritableComparator.get(keyclass)</tt>.</p> |
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| 291 | |
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| 292 | <p>Users can specify their own join operations, typically by overriding |
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| 293 | <tt>JoinRecordReader</tt> or <tt>MultiFilterRecordReader</tt> and mapping that |
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| 294 | class to an identifier in the join expression using the |
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| 295 | <tt>mapred.join.define.<em>ident</em></tt> property, where <em>ident</em> is |
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| 296 | the identifier appearing in the join expression. Users may elect to emit- or |
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| 297 | modify- values passing through their join operation. Consulting the existing |
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| 298 | operations for guidance is recommended. Adding arguments is considerably more |
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| 299 | complex (and only partially supported), as one must also add a <tt>Node</tt> |
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| 300 | type to the parse tree. One is probably better off extending |
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| 301 | <tt>RecordReader</tt> in most cases.</p> |
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| 302 | |
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| 303 | <a href="http://issues.apache.org/jira/browse/HADOOP-2085">JIRA</a> |
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| 304 | <P> |
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| 305 | |
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| 306 | <P> |
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