Explain planning in Amazon Athena.
💡 Model Answer
Amazon Athena is a serverless, interactive query service that uses Presto under the hood to run SQL queries against data stored in Amazon S3. When you submit a query, Athena’s query planner performs several steps:
- Parsing – The SQL is parsed into a syntax tree.
- Semantic Analysis – The planner checks for schema validity, resolves table and column names, and infers data types.
- Logical Plan Creation – A logical representation of the query is built, showing operations like scans, joins, filters, and aggregations.
- Optimization – The planner applies rule‑based and cost‑based optimizations such as predicate pushdown, column pruning, and partition pruning to reduce the amount of data read from S3.
- Physical Plan Generation – The logical plan is translated into a physical execution plan that Presto can run, selecting specific execution engines and data formats.
Athena’s planner is designed to be lightweight because it operates on immutable data in S3. It relies heavily on metadata from the Glue Data Catalog and statistics about partitions to make efficient decisions. The result is a query that reads only the necessary data, minimizing cost and latency.
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