IBM InfoSphere DataStage Interview Questions - Sequential File Stage

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IBM InfoSphere DataStage Interview Questions

Sequential File Stage



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DataStage Interview Questions



Question 1:

What is a Sequential File Stage in DataStage?
Answer:
Sequential File Stage is used to read data from or write data to flat files (like CSV, TXT). It acts as a source or target in DataStage jobs and supports both sequential and parallel processing.

Question 2:

What are the main purposes of Sequential File Stage?
Answer:

  • Reading input files
  • Writing output files
  • Data exchange between systems
  • Handling structured text data

Question 3:

What types of files can Sequential File Stage handle?
Answer:

  • CSV files
  • Fixed-width files
  • Delimited files
  • Text files

Question 4:

What are the modes available in Sequential File Stage?
Answer:

  • Read Mode
  • Write Mode

Question 5:

What is the difference between Read and Write mode?
Answer:

  • Read Mode: Reads data from file into DataStage
  • Write Mode: Writes processed data into file

Question 6:

What is the “File” property in Sequential File Stage?
Answer:
It specifies the path and name of the file to read or write.

Question 7:

What are update options in Sequential File Stage?
Answer:

  • Create (Error if exists)
  • Overwrite
  • Append
  • Use Existing

Question 8:

Explain “Create (Error if exists)”.
Answer:
Creates a new file. If file already exists, job fails.

Question 9:

Explain “Overwrite”.
Answer:
Deletes existing file and creates a new one with fresh data.

Question 10:

Explain “Append”.
Answer:
Adds new data at the end of existing file without deleting previous data.

Question 11:

Explain “Use Existing”.
Answer:
Uses existing file without modifying structure; may discard schema or records.

Question 12:

What is “First Row is Column Names”?
Answer:
Indicates that first row contains column headers instead of data.

Question 13:

What is a delimiter?
Answer:
A character used to separate columns (e.g., comma, tab, pipe).

Question 14:

What is default delimiter in Sequential File Stage?
Answer:
Comma (,) for CSV files.

Question 15:

What is a fixed-width file?
Answer:
File where each column has predefined width instead of delimiters.

Question 16:

What is “Quote Character”?
Answer:
Used to enclose string values, typically double quotes (" ").

Question 17:

What is “Null Field Value”?
Answer:
Defines how null values are represented in file (e.g., NULL or empty).

Question 18:

What is “Record Level”?
Answer:
Defines how records are structured in file (line-by-line storage).

Question 19:

What is “Header” in Sequential File?
Answer:
Lines at beginning of file containing metadata or column names.

Question 20:

What is “Footer”?
Answer:
Lines at end of file (e.g., record count summary).

Question 21:

How to skip header rows in Sequential File Stage?
Answer:
Use property “Header Rows to Skip”.

Question 22:

How to read only specific rows?
Answer:
Using constraints or external commands (like sed).

Question 23:

What is “Encoding”?
Answer:
Defines character set (UTF-8, ASCII, etc.).

Question 24:

What happens if file encoding is wrong?
Answer:
Data corruption or unreadable characters may occur.

Question 25:

What is “Format” option?
Answer:
Defines file format (Delimited, Fixed Width).

Question 26:

What is “Schema”?
Answer:
Structure of data (columns, data types).

Question 27:

What is “Reject Link”?
Answer:
Captures rejected records during processing.

Question 28:

What is “Sequential Processing”?
Answer:
Data processed row-by-row in order.

Question 29:

Can Sequential File Stage work in parallel jobs?
Answer:
Yes, it supports parallel processing.

Question 30:

What is partitioning in Sequential File Stage?
Answer:
Distributes data across nodes for parallel processing.

Question 31:

Types of partitioning supported?
Answer:

  • Auto
  • Hash
  • Round Robin
  • Entire
  • Same
  • Random
  • Range
  • Modulus

Question 32:

What is “Auto Partition”?
Answer:
System automatically decides partitioning method.

Question 33:

What is “Hash Partition”?
Answer:
Data distributed based on hash of key column.

Question 34:

What is “Round Robin”?
Answer:
Data evenly distributed across nodes sequentially.

Question 35:

What is “Entire Partition”?
Answer:
All data goes to a single node.

Question 36:

What is “Same Partition”?
Answer:
Maintains same partitioning as previous stage.

Question 37:

What is “Random Partition”?
Answer:
Data distributed randomly.

Question 38:

What is “Range Partition”?
Answer:
Data divided based on value ranges.

Question 39:

What is “Modulus Partition”?
Answer:
Data distributed using modulus function.

Question 40:

What is data skew?
Answer:
Uneven data distribution across nodes.

Question 41:

How to handle data skew?
Answer:

  • Use proper partitioning
  • Choose correct key
  • Rebalance data

Question 42:

What is “File Pattern”?
Answer:
Used to read multiple files using wildcard (e.g., *.csv).

Question 43:

What is “File Set”?
Answer:
Collection of multiple files treated as one dataset.

Question 44:

What is “Sequential File Stage vs Dataset Stage”?
Answer:

  • Sequential: External flat file
  • Dataset: Internal high-performance storage

Question 45:

Can we compress files in Sequential File Stage?
Answer:
Yes, using gzip or external tools.

Question 46:

What is “Buffering”?
Answer:
Temporary storage to improve I/O performance.

Question 47:

What is “APT_CONFIG_FILE”?
Answer:
Defines node configuration for parallel jobs.

Question 48:

What is “Node”?
Answer:
Processing unit in parallel job.

Question 49:

How to improve performance of Sequential File Stage?
Answer:

  • Use partitioning
  • Avoid unnecessary columns
  • Use buffering
  • Optimize file format

Question 50:

What are real-time use cases of Sequential File Stage?
Answer:

  • Loading CSV into database
  • Exporting reports
  • Data migration
  • File-based integration

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