Databricks Data Engineer Professional Question 119
Select 3A data engineering team is running a Spark job on a Delta table containing billions of records, but they observe high query latency and suboptimal performance. Upon investigation, they find that the table has a large number of small files due to frequent updates and overpartitioning. Which of the following issues are likely caused by the presence of these small files?
- A
Increased job execution time due to higher metadata overhead during query planning.
- B
Higher memory consumption on Spark executors due to the need to load multiple small files.
- C
Improved query performance because small files distribute the workload across more Spark tasks.
- D
Increased I/O operations and network overhead due to processing a large number of small files.
- E
Reduced shuffle spill as small files reduce the size of partitions involved in shuffles.
Show answer and explanation
Correct answers: A, B, D
Explanation
The presence of small files in a Spark job leads to inefficiencies such as increased metadata overhead during query planning, higher memory consumption on executors, and additional I/O and network overhead. These factors degrade query performance, making it essential to optimize data layout using techniques like file compaction or partition pruning.
- A. Correct.
Correct: A large number of small files increases metadata overhead for the Spark driver, as it must scan and plan for each file, leading to higher job execution time.
- B. Correct.
Correct: Small files require Spark executors to open and process many files, increasing memory consumption as more file handles and associated data structures are loaded.
- C. Incorrect.
Incorrect: Small files do not inherently improve performance. Instead, they cause inefficiencies by creating unnecessary overhead, contrary to distributing the workload effectively.
- D. Correct.
Correct: Processing a large number of small files results in higher I/O operations and network overhead, as Spark must read scattered data from disk and shuffle it across nodes.
- E. Incorrect.
Incorrect: Small files do not reduce shuffle spill. The size of partitions during shuffles depends on the data distribution, not the size of the files themselves.