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Both sides previous revision Previous revision 2012/01/31 16:25 dusek 2012/01/31 16:24 dusek 2012/01/31 12:16 straka 2012/01/31 12:13 straka 2012/01/31 11:48 straka 2012/01/31 11:47 straka 2012/01/31 11:43 straka 2012/01/31 11:42 straka 2012/01/31 11:39 straka 2012/01/31 11:29 straka 2012/01/31 11:28 straka 2012/01/31 11:27 straka 2012/01/31 09:52 straka Change Java commandline syntax.2012/01/30 15:38 majlis 2012/01/30 15:04 majlis 2012/01/28 17:55 straka 2012/01/27 23:57 straka 2012/01/27 23:48 straka 2012/01/27 23:47 straka 2012/01/27 23:46 straka 2012/01/27 22:20 straka 2012/01/27 22:17 straka 2012/01/27 22:17 straka 2012/01/27 22:16 straka 2012/01/27 22:16 straka 2012/01/27 22:08 straka 2012/01/27 22:08 straka 2012/01/27 22:01 straka 2012/01/27 21:56 straka 2012/01/27 21:52 straka 2012/01/27 21:47 straka 2012/01/27 21:41 straka 2012/01/27 21:32 straka 2012/01/27 21:28 straka 2012/01/27 21:28 straka 2012/01/27 21:27 straka 2012/01/27 21:27 straka 2012/01/27 21:02 straka 2012/01/27 21:01 straka 2012/01/27 20:56 straka 2012/01/27 20:40 straka 2012/01/27 20:11 straka vytvořeno Go Next revision		Previous revision 2012/01/31 16:25 dusek 2012/01/31 16:24 dusek 2012/01/31 12:16 straka 2012/01/31 12:13 straka 2012/01/31 11:48 straka 2012/01/31 11:47 straka 2012/01/31 11:43 straka 2012/01/31 11:42 straka 2012/01/31 11:39 straka 2012/01/31 11:29 straka 2012/01/31 11:28 straka 2012/01/31 11:27 straka 2012/01/31 09:52 straka Change Java commandline syntax.2012/01/30 15:38 majlis 2012/01/30 15:04 majlis 2012/01/28 17:55 straka 2012/01/27 23:57 straka 2012/01/27 23:48 straka 2012/01/27 23:47 straka 2012/01/27 23:46 straka 2012/01/27 22:20 straka 2012/01/27 22:17 straka 2012/01/27 22:17 straka 2012/01/27 22:16 straka 2012/01/27 22:16 straka 2012/01/27 22:08 straka 2012/01/27 22:08 straka 2012/01/27 22:01 straka 2012/01/27 21:56 straka 2012/01/27 21:52 straka 2012/01/27 21:47 straka 2012/01/27 21:41 straka 2012/01/27 21:32 straka 2012/01/27 21:28 straka 2012/01/27 21:28 straka 2012/01/27 21:27 straka 2012/01/27 21:27 straka 2012/01/27 21:02 straka 2012/01/27 21:01 straka 2012/01/27 20:56 straka 2012/01/27 20:40 straka 2012/01/27 20:11 straka vytvořeno Go Next revision Both sides next revision
courses:mapreduce-tutorial:step-24 [2012/01/27 22:08] straka		courses:mapreduce-tutorial:step-24 [2012/01/27 23:47] straka
Line 80:		Line 80:
	</file>		</file>
-	Remarks:	+	=== Remarks ===
	* The filename //must// be the same as the name of the class -- this is enforced by Java compiler.		* The filename //must// be the same as the name of the class -- this is enforced by Java compiler.
	* In one class multiple jobs can be submitted, either in sequence or in parallel.		* In one class multiple jobs can be submitted, either in sequence or in parallel.
	* A mismatch of types is usually detected by the compiler, but sometimes it is detected only at runtime. If that happens, an exception is raised and the program crashes. For example, default key output class it ''LongWritable'' -- if ''Text'' was not specified, the program would crash.		* A mismatch of types is usually detected by the compiler, but sometimes it is detected only at runtime. If that happens, an exception is raised and the program crashes. For example, default key output class it ''LongWritable'' -- if ''Text'' was not specified, the program would crash.
		+	* **VIM users**: The code completion plugin does not complete the ''context'' variable. That is because it does not understand that ''Context'' is used as an abbreviation for ''MapContext<Text, Text, Text, Text>''. If the type ''MapContext<Text, Text, Text, Text>'' is used instead of ''Context'', the code compiles and code completion on ''context'' works.
	===== Running the job =====		===== Running the job =====
Line 93:		Line 94:
	===== Exercise =====		===== Exercise =====
	Download the ''MapperOnlyHadoopJob.java'', compile it and run it using		Download the ''MapperOnlyHadoopJob.java'', compile it and run it using
-	/net/projects/hadoop/bin/hadoop -r 0 MapperOnlyHadoopJob	+	/net/projects/hadoop/bin/hadoop -r 0 MapperOnlyHadoopJob.jar /home/straka/wiki/cs-text-small outdir
		+
		+	Mind the ''-r 0'' switch -- specifying ''-r 0'' disable the reducer. If the switch ''-r 0'' was not given, one reducer of default type ''IdentityReducer'' would be used. The ''IdentityReducer'' outputs every (key, value) pair it is given.
		+	* When using ''-r 0'', the job runs faster, as the mappers write the output directly to disk. Buth there are as many output files as mappers and the (key, value) pairs are stored in no special order.
		+	* When not specifying ''-r 0'' (i.e., using ''-r 1'' with ''IdentityReducer''), the job produces the same (key, value) pairs. But this time they are in one output file, sorted according to the key. Of course, the job runs slower in this case.

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