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ETL Interview Questions and Answers

1
What is ETL process? How many steps ETL contains? Explain with example.
  • ETL stands for Extraction, Transforming and Loading.
  • Data is extracted from the source(database servers), and applied for generating business role on it.

The following are the steps involved :

  • Define the source [ define the odbc connection to the database source ]
  • Define the target [ create the odbc connection to the target database ]
  • Create the mapping [ Apply business role here by adding transformations and define the data flow from source to target ]
  • Create the session [ Mapping instructions ]
  • Create the work flow [ Instructions that run on the sessions ]
2
Explain what are the ETL testing operations includes?

ETL testing includes

  • Verify whether the data is transforming correctly according to business requirements
  • Verify that the projected data is loaded into the data warehouse without any truncation and data loss
  • Make sure that ETL application reports invalid data and replaces with default values
  • Make sure that data loads at expected time frame to improve scalability and performance
3
What are the out put files that the informatica server creates during the session running?
  • Informatica server log: A log is created for all status and error messages. It also creates error log for error messages and are created in Informatica home directory.
  • Session log file: Every session is assigned to a session log file. It persists information about sessions into log files.
  • Session detail file: It has the statistics of loading for every target in mapping. The session details include information about table name, no. of rows writer or rejected.
  • Performance detail file: The information about session performance details that helps to improve the performance. Select ‘ Performance Details’ option in the session property sheet.
  • Reject file: Reject file contains the data of rows which the writer does not write to targets.
4
In case you have non-OLEDB (Object Linking and Embedding Database) source for the lookup what would you do?

In case if you have non-OLEBD source for the lookup then you have to use Cache to load data and use it as source

5
What is Full load & Incremental or Refresh load?
  • Initial Load : It is the process of populating all the data warehousing tables for the very first time
  • Full Load : While loading the data for the first time, all the set records are loaded at a stretch depending on the volume. It erases all the contents of tables and reloads with fresh data
  • Incremental Load : Applying the dynamic changes as and when necessary in a specific period. The schedule is predefined each period
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