How do you partition data in Amazon S3?

S3 itself is a flat object store, but you can logically partition data by using folder prefixes in the object key. For example, store logs as s3://bucket/logs/year=2024/month=08/day=16/… .

When you query the data with services that understand partitions (Athena, Redshift Spectrum, EMR, Glue), you define a table with partition columns that map to those prefixes. The query engine then scans only the relevant partitions, improving performance and reducing cost.

Typical steps:

1. Choose a partition key (date, region, user ID, etc.).
2. Write data to S3 using the key format: s3://bucket/table/partition_key=value/…
3. Register the table in Athena/Glue with the partition columns.
4. Run a MSCK REPAIR TABLE or ALTER TABLE ADD PARTITION to load the partitions.

You can also use tools like AWS Lake Formation or Glue Crawlers to automate partition discovery. Partitioning is especially useful for large datasets where queries filter on the partition key.