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Mapreduce Basics Hadoop Counters Hadoop Log Info(slf4j) Unit Test(JUnit, MRUnit) Guava(Google Core Libraries for Java
1.6+) Others References
Overview
Hadoop job submit flow
Mapreduce Basics
Hadoop Web GUI
Mapreduce Basics
Hadoop job submit flow
Mapreduce Basics
1. Invisible to details2. None step-through Debug
If errors?
Not just pray!
Command Errors, Grammar Errors Check, and check, and check again…
Logic Errors That is the point that we need to deal
with.
Errors
First, We need to check our mapreduce outputs.
Hadoop Standard Counters Map output records Reduce output records
Custom Counters
Hadoop Counters
How to custom a mapreduce counter?
context.getCounter(counterName);context.getCounter(groupName, counterName);
输入文件
How to custom a mapreduce counter?
Second, We need
more output information to check
our programs.
Stdout does not work. System.out.println() X
Use Logger. Eg: log4j, slf4j
Hadoop Log Info
SLF4j – Simple Logging Façade for Java.
Simple, easy to use.
Hadoop Log Info – Slf4j
Hadoop Log Info – Slf4j
But, we still want to assume the
correctness before we run the programs.
TDD, Test-Driven Development,
Unit Test
TDD encourages simple designs and inspires
confidence.
JUnit(Unit Test for Java) #Unit(for C#) XUnit
Unit Test – JUnit
小孩分油问题：两个小孩去打油，一人带了一个一斤的空瓶，另一个带了一个七两、一个三两的空瓶。原计划各打一斤油，可是由于所带的钱不够，只好两人合打了一斤 (10两 )油，在回家的路上，二人想平分这一斤油，可是又没有其它工具。试仅用三个瓶子 (一斤、七两、三两 )精确地分出两个半斤油来。
How to write unit tests using JUnit?
Define a state: Each represents the 10 ounces,
7ounces, and 3 ounces bottle. Define the Operation：
multiAndPlus(X, b) Eg: pour 10 ounces from the first(10o)
bottle to the third one.
How to write unit tests using JUnit?
How to write unit tests using JUnit?
MatTest.java
Mat.java
@Test @Before, @After Assert*
And last, RUN in Java Normal Application.
How to write unit tests using JUnit?
MRUnit, Unit Test for Hadoop Mapreduce
Unit Test - MRUnit
MapDriver ReduceDriver MapReduceDriver
withInput(key, value) withOutput(key, value) runTest()
And last, RUN in Java Normal Application.
How to write unit test using MRUnit?
And then, we also want to
assume the correctness
in our programs.
The Art of Assertion in CH5 of Programming Pearls, Second Edition.
Assert in Java assert <boolean expression> assert <boolean expression> : <error
message>
But, you must run the application with enabling assertions implicitly.(java -ea <className>)
Precondition in Guava
Assertions
Guava, Google Core Libraries for Java 1.6+
Preconditions
Preconditions in Guava
checkArgument(i >= 0, "Argument was %s but expected nonnegative", i);checkArgument(i < j, "Expected i < j, but %s > %s", i, j);
Other useful libraries.
Guava
http://code.google.com/p/guava-libraries/
How to custom a partitioner in hadoop?
自定义数据类型 CustomType
自定义 Partitioner
How to custom a partitioner in hadoop?
How to custom a partitioner in hadoop?
Partitioner: return Key % 3
When change to: (return key / 3), and change the number of reduce tasks to 4
Totally ordering.
Maven Auto endependency management
Hadoop Remote Debug JDWP, Java Debug Wire Protocol
HPROF Analysis tools in JDK
Others
Hadoop, the Definitive Guide, Second Edition.
http://www.junit.org/ http://incubator.apache.org/mrunit/ http://code.google.com/p/guava-
libraries/ http
://insightfullogic.com/blog/2011/oct/21/5-reasons-use-guava/
References
Thank you for your time!
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