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Data Migration Interview
Questions

25 Questions and Answers by William Swansen

Published March 17th, 2020 | William Swansen is an author, job search strategist and career advisor who assists individuals from all over the world.
Question 1 of 25
What then is meant by an incremental load?
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How to Answer
This is a follow-up to the previous question. When an interviewer has a particular interest in a topic or wants to dig deeper into your knowledge of the subject, they will ask follow-up questions. You should be prepared for follow-up questions any time you've provided an answer to the interviewer.
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1.
What then is meant by an incremental load?
This is a follow-up to the previous question. When an interviewer has a particular interest in a topic or wants to dig deeper into your knowledge of the subject, they will ask follow-up questions. You should be prepared for follow-up questions any time you've provided an answer to the interviewer.

William's Answer #1
"Incremental load refers to applying dynamic changes after the initial or full load process. These are performed as needed or when required in a specific period or on predefined schedules."
William's Answer #2
"In incremental load refers to the process of populating the data warehouse tables after the initial load or full load has been performed. Any subsequent migration of data into the tables is considered an incremental load. These can be ad hoc or on predefined schedules."
2.
Can you explain the differences between a connected and an unconnected lookup and when you should use each of them in a data migration?
This question asks you to compare two similar but different terms and to discuss when to use them in data migration. This is a typical operational question which starts with a definition and then asks you to describe how you would apply it. As a seasoned data migration operator, you should be able to answer this question easily.

William's Answer #1
"The two types of lookups are called connected and disconnected. A connected looked up is used for mapping and will return multiple values. It is called connected because it can be tied to another transformation. On the other hand, and unconnected lookup is used when it cannot be connected to another transformation. It returns a single value, but it is reusable."
William's Answer #2
"Connected and unconnected lookups or similar but slightly different. They both query the tables and provide values as a result of the operation. The difference is that connected lookups are part of the workflow and can be tied to another transformation. Unconnected lookups only provide a single output and cannot be connected to other operations. Both types of lockups can be reused if necessary."
3.
Please define the term workflow and discuss how it is used in the context of data migration?
This is a straightforward question, which by now you should recognize as another technical question. You should be very adept that answering this type of question at this point in the interview. Keep your answer concise and to the point, and allow the interviewer to ask a follow-up question if they are more interested in this topic.

William's Answer #1
"Workflow is simply the set of instructions that determines how the tasks are executed during a data migration process. Defining an effective workflow makes the process more efficient."
William's Answer #2
"In the context of a data migration project, the term workflow refers to the progression of tasks that are executed during the data migration. Creating an efficient workflow expedites the migration process and results in a table within the data warehouse, which is more useful and has greater integrity."
4.
How do you fine-tune the mapping of the data during data migration?
By asking this question, the interviewer is indicating that this topic is important to them. Hopefully, your pre-interview research helped you to discover this, so you're prepared to address this question.

William's Answer #1
"There are several steps involved in the fine-tuning of the mapping of data during a migration process. You can use a filter to qualify the data, utilize persistence to create a cache during the lookup operation, aggregate the data, sort it by a group, and use operators' when writing the functions. Another technique is to increase the cache size and commit intervals."
William's Answer #2
"When mapping the data during a data migration, you can fine-tune it to increase the performance and reduce the retrieval time. Techniques available include filtering, qualifying, used utilizing caches, aggregating the data, sorting it into groups, and utilizing operators within your functional expressions. You can also increase the cache size and the commit intervals to optimize the mapping process."
5.
How are the tables in data migration analyzed, and when does the analysis occur?
There is another technical question that contains two parts; the first being a how which is a process question the next being a when which is it clarifying question. You're reminded to answer every part of a question which an interviewer asks, especially with a technically-oriented interview. Doing this demonstrates both your listening skills as well as your attention to detail.

William's Answer #1
"The tables in a data migration process are analyzed by reviewing the statistics generated using the analyze command. The same statistics can be used by a cost-based optimizer to create a data retrieval plan. The analyze statement also supports the creation of the object's structures, space management, and other operations within the data warehouse tables. The tables are analyzed either when the index table is created or when the cluster is complete."
William's Answer #2
"The analyst managing a data migration process use statistics to analyze the tables in the data tables. They use the analyze command to perform this function. The information generated by analyze can also help to optimize how the data is retrieved and make the process more effective. The best time to analyze the tables is when the index table is first created or after the cluster is complete."
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