Federated queries

Federated queries allow you to query data stored in external systems without first loading it (ETL) into YDB. The most popular use case is working with data in S3-compatible object storage.

How it works

You can create an external table in YDB that references data in S3. When you execute a SELECT query against such a table, YDB initiates a parallel read from all compute nodes. Each node reads and processes only the portion of data it needs.

• Supported formats: Parquet, CSV, JSON with various compression algorithms.
• Read optimization: YDB uses S3 data read optimization mechanisms (partition pruning) for Hive-style partitioning and for more complex partitioning schemes.