# Scaling Model Evaluation at Pinterest with Ray Pinterest optimizes machine learning evaluation by fusing inference and metric computation using Ray. - **Source:** [Pinterest Engineering](https://medium.com/pinterest-engineering) - **Published:** 2026-11-04 - **Topic:** [technology](https://brifing.si/c/technology) - **Original article:** - **On Brifing:** https://brifing.si/s/67ddf894-de51-4ddc-a198-c54586c22c84 ## The Evaluation Bottleneck Pinterest engineers identified that traditional machine learning evaluation pipelines often suffer from significant overhead. By separating inference and metric computation into distinct stacks, systems incur costs from cluster startup times and redundant data movement. Writing predictions to S3 and reading them back for evaluation creates a performance gap that hinders scaling experiments. ## Fusing Inference and Metrics The team implemented a fused architecture where metrics are computed directly within the Ray inference job. By utilizing a shared object store, they eliminate the need for cross-stack serialization and deserialization. This approach allows the system to overlap metric computation with inference, effectively utilizing CPU resources that would otherwise remain idle. ## Metric Contract Definition To standardize evaluation, Pinterest defined a common metric contract using an Abstract Base Class. This interface requires three methods: dataset preprocessing, partial result computation, and reduction. This design ensures that metrics can be calculated across distributed batches, providing a consistent interface regardless of the underlying execution framework used for the specific experiment. ## Decomposable Metric Strategy Decomposable metrics, such as Mean Absolute Error, allow for independent batch processing because they do not require row colocation. The system calculates partial sums and row counts for each batch, which are then aggregated globally. This method avoids the need for a global dataset view, making it highly efficient for large-scale production workflows. ## Handling Holistic Metrics Holistic metrics like ROC-AUC traditionally require a global sort, which is computationally expensive. Pinterest approximates this by using a threshold-based confusion matrix approach. By calculating confusion matrices per batch and summing them, the system achieves accurate results without the performance penalty of a full global sort across all inference experiments. ## Group-wise Metric Constraints Precision@K requires grouping data by segments, such as specific user requests. To handle this, the team introduced buckets, which are group-preserving batches. This ensures that no segment spans across different buckets, allowing the system to maintain semantic integrity while still enabling efficient parallel computation across the distributed Ray worker nodes. ## Optimizing Resource Utilization The fused pipeline design significantly improves hardware efficiency. Since GPU-intensive inference tasks often leave CPU workers underutilized, interleaving metric computation allows the system to perform both tasks concurrently. This architectural shift minimizes idle time and ensures that the compute resources are saturated throughout the entire duration of the model evaluation process. ## Scaling Feature Importance Feature importance systems, which run numerous perturbation-based experiments, benefit greatly from this architecture. By quantifying how input features contribute to predictions, the system must aggregate metrics over massive volumes of data. The fused approach allows these experiments to scale linearly, maintaining performance even as the number of model heads and experiments increases. ## Performance Benchmarking Results The implementation of this fused evaluation platform resulted in a substantial performance improvement. By amortizing the metrics compute step and overlapping it with inference, the team successfully reduced end-to-end evaluation time by up to 32 percent. This efficiency gain is critical for maintaining rapid iteration cycles in large-scale machine learning production environments. ## Infrastructure Challenges As machine learning workflows grow, evaluation transforms from a simple task into a complex infrastructure challenge. Systems must manage large volumes of inference data while maintaining low latency. Pinterest's solution demonstrates that treating decomposability as a first principle is essential for building robust, scalable platforms that can handle diverse metric requirements. ## Ray as a Framework Ray serves as the last-mile data processing framework for Pinterest's ML stack. Beyond batch inference, its ability to handle complex task dependencies and shared memory makes it ideal for metric aggregation. The integration into existing training infrastructure highlights Ray's versatility in solving bottlenecks that arise when scaling deep learning models in production. ## Future Evaluation Outlook The successful fusion of inference and evaluation sets a new standard for Pinterest's ML platform. By prioritizing efficient data layouts and minimizing serialization, the team has created a flexible system capable of supporting future growth. This architecture provides a blueprint for other organizations facing similar challenges in scaling complex model evaluation pipelines. ## Sources covering this story - https://medium.com/pinterest-engineering/scaling-model-evaluation-at-pinterest-with-ray-part-4-4a96cd12cc11?source=rss----4c5a5f6279b6---4 — --- _Summary written by Brifing from the original reporting. Copyright in the original article belongs to its publisher; read the full piece at the link above._