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The Ultimate Cheat Sheet On Hadoop

Top 20 frequently asked questions to test your Hadoop knowledge given in the below Hadoop cheat sheet. Try finding your own answers and match the answers given here.




Question #1 

You have written a MapReduce job that will process 500 million input records and generate 500 million key-value pairs. The data is not uniformly distributed. Your MapReduce job will create a significant amount of intermediate data that it needs to transfer between mappers and reducers which is a potential bottleneck. A custom implementation of which of the following interfaces is most likely to reduce the amount of intermediate data transferred across the network?



A. Writable
B. WritableComparable
C. InputFormat
D. OutputFormat
E. Combiner
F. Partitioner
Ans: e




Question #2 

Where is Hive metastore stored by default ?


A. In HDFS
B. In client machine in the form of a flat file.
C. In client machine in a derby database
D. In lib directory of HADOOP_HOME, and requires HADOOP_CLASSPATH to be modified.
Ans: c




Question…

PL SQL: How to Fix Errors

PL/SQL is procedural language, and the PL/SQL procedures you can call from any high-level language. This is depending on your project requirement.
PL SQL Errors tips to avoid
PL SQL 
How to prevent some common errors or exceptions while writing PL/SQL procedures in your project.
  • The number one and primary one is assigning variables non-numeric to numeric. This is one kind of area where you need to look in while writing PL/SQL procedure.
  • PL/SQL is nothing but an invitation for trouble. They are all centered on data types and implicit conversion.

What's implicit conversion?

Let's say you have number held in a varchar2 data type variable, v_value. You try assigning n_value, a number data type variable, that value with the following line of code:n_value := v_value;

That should work, right?

Yes, it should, but when it doesn't, because you don't actually have a numeric literal stored in variable v_value, the implicit data type conversion will raise an "unexpected" exception in your program unit.
Another most common issue is assigning DATE field to numeric field while writing PL/SQL procedure. Usually, it will not work, and it will through a conversion error.

You want to pass a date value to a function that will return the time in seconds since midnight, January 1, 1980. The function requires the date be passed as a varchar2 parameter in the form DD-MON-YY.
```sql
d_value date := sysdate;
n_value number;
```     
```sql

BEGIN
n_value := date_to_long(d_value);

```      

Sample PL/SQL

  1. Oracle's default date format is DD-MON-YY, so it will work fine, right?
  2. Not exactly. If the current NLS_DATE_FORMAT for the session is DD-MON-YY (the default), it will work, but not if it is YYYYMMDD HH24MISS, as I set mine every time I log in to SQL*Plus.
  3. The above two kinds of errors you can avoid as a preventive measure while writing your PL/SQL procedure.

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