Klenzaids Interview Questions and Answers

inferschema in pyspark is used to automatically infer the schema of a file when reading it.

• inferschema is a parameter in pyspark that can be set to true when reading a file to automatically infer the schema based on the data

• It is useful when the schema of the file is not known beforehand

• Example: df = spark.read.csv('file.csv', header=True, inferSchema=True)

SCD stands for Slowly Changing Dimension in Data Warehousing.

• SCD is a technique used in data warehousing to track changes to dimension data over time.

• There are different types of SCDs - Type 1, Type 2, and Type 3.

• Type 1 SCD overwrites old data with new data, Type 2 creates new records for changes, and Type 3 maintains both old and new values in separate columns.

• Example: In a customer dimension table, if a customer changes their address, a Type 2 SCD would create a new record ...read more

Optimizing techniques in Spark involve partitioning, caching, and tuning resources for efficient data processing.

• Use partitioning to distribute data evenly across nodes for parallel processing

• Cache frequently accessed data in memory to avoid recomputation

• Tune resources such as memory allocation and parallelism settings for optimal performance

Repartition is used to increase the number of partitions in a DataFrame, while coalesce is used to decrease the number of partitions.

• Repartition involves shuffling data across the network, which can be expensive in terms of performance and resources.

• Coalesce is a more efficient operation as it minimizes data movement by only merging existing partitions.

• Repartition is typically used when there is a need for more parallelism or to evenly distribute data for better performance.

• C...read more

Normalization in databases is the process of organizing data in a database to reduce redundancy and improve data integrity.

• Normalization is used to eliminate redundant data and ensure data integrity.

• It involves breaking down a table into smaller tables and defining relationships between them.

• There are different normal forms such as 1NF, 2NF, 3NF, and BCNF.

• Normalization helps in reducing data redundancy and improving query performance.

• Example: In a database, instead of storing...read more

Transformation involves changing the data structure, while action involves performing a computation on the data.

• Transformation changes the data structure without executing any computation

• Action performs a computation on the data and triggers the execution

• Examples of transformation include map, filter, and reduce in Spark or Pandas

• Examples of action include count, collect, and saveAsTextFile in Spark