PrestoDB Interview Questions and Answers for 2 years experience

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PrestoDB Interview Questions & Answers

  1. What is PrestoDB and what are its key features?

    • Answer: PrestoDB is a distributed SQL query engine for running interactive analytic queries against data sources of various sizes ranging from gigabytes to petabytes of data. Key features include its speed and efficiency in handling large datasets, support for various data sources (e.g., Hive, S3, Cassandra), scalability, fault tolerance, and its ability to perform complex queries with good performance.

  2. Explain the architecture of PrestoDB.

    • Answer: PrestoDB employs a distributed, master-worker architecture. A coordinator node manages the query execution plan and distributes tasks to worker nodes. Each worker node processes a portion of the query and sends results back to the coordinator. This allows for parallel processing and high throughput.

  3. How does PrestoDB handle data from different sources? (e.g., Hive, S3, Cassandra)?

    • Answer: PrestoDB uses connectors to interact with various data sources. Each connector is responsible for understanding the specifics of a particular data source and translating PrestoDB's SQL queries into the appropriate commands for that source. This allows PrestoDB to query data from multiple sources seamlessly.

  4. What are the different types of joins in PrestoDB and their performance implications?

    • Answer: PrestoDB supports various joins like INNER JOIN, LEFT JOIN, RIGHT JOIN, FULL OUTER JOIN. Performance depends on data size and distribution. For large datasets, using optimized join algorithms (e.g., broadcast joins for smaller datasets, hash joins for larger datasets) is crucial for performance. Properly choosing join type and indexing can significantly impact query speed.

  5. Explain the concept of Cost-Based Optimization in PrestoDB.

    • Answer: PrestoDB's query optimizer uses cost-based optimization to select the most efficient query execution plan. It estimates the cost of different plans based on factors like data size, available resources, and statistics gathered from the data source. This enables the optimizer to choose the plan with the lowest estimated cost, leading to improved performance.

  6. How do you handle NULL values in PrestoDB?

    • Answer: NULL values are handled according to standard SQL semantics. Functions like IS NULL, COALESCE, and NVL can be used to check for or replace NULL values. Comparisons involving NULLs typically result in UNKNOWN, impacting the outcome of boolean expressions.

  7. Describe different data types supported by PrestoDB.

    • Answer: PrestoDB supports a variety of data types including BOOLEAN, TINYINT, SMALLINT, INTEGER, BIGINT, REAL, DOUBLE, VARCHAR, CHAR, DATE, TIME, TIMESTAMP, etc. The specific data types and their precision may depend on the underlying data source connector.

  8. Explain the use of UDFs (User-Defined Functions) in PrestoDB.

    • Answer: UDFs allow you to extend PrestoDB's functionality by creating custom functions written in Java, Scala, or other supported languages. These functions can perform complex operations or transformations not readily available as built-in functions. They can be registered and used within SQL queries.

  9. How do you optimize query performance in PrestoDB?

    • Answer: Query optimization involves various strategies like using appropriate join types, indexing (where applicable), optimizing data partitioning, using appropriate data types, employing predicate pushdown, avoiding unnecessary subqueries, analyzing query execution plans, leveraging caching and efficient data structures, and writing efficient UDFs.

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