Presto QUERY_EXCEEDED_MEMORY_LIMIT

What is Presto QUERY_EXCEEDED_MEMORY_LIMIT

Understanding Presto: A High-Performance SQL Query Engine

Presto is an open-source distributed SQL query engine designed for running interactive analytic queries against data sources of all sizes. It is optimized for low-latency and high-throughput, making it ideal for big data analytics. Presto can query data where it lives, including Hive, Cassandra, relational databases, or even proprietary data stores.

Identifying the Symptom: QUERY_EXCEEDED_MEMORY_LIMIT

When using Presto, you might encounter the error code QUERY_EXCEEDED_MEMORY_LIMIT. This error typically manifests when a query consumes more memory than the allocated limit, causing the query to fail. Users will see this error message in the query logs or the Presto UI.

Exploring the Issue: Memory Limit Exceeded

The QUERY_EXCEEDED_MEMORY_LIMIT error indicates that the query has surpassed the memory threshold set for execution. Presto allocates a specific amount of memory for each query to ensure efficient resource utilization and prevent any single query from monopolizing system resources. When this limit is breached, Presto aborts the query to maintain system stability.

Why Does This Happen?

This issue can occur due to several reasons, such as inefficient query design, large data sets, or insufficient memory allocation. Complex queries with multiple joins or aggregations are more likely to hit this limit.

Steps to Resolve the QUERY_EXCEEDED_MEMORY_LIMIT Issue

1. Optimize Your Query

Review your query for any inefficiencies. Simplifying the query, reducing the number of joins, or breaking down complex queries into smaller parts can help. Consider using Presto's SQL functions to optimize query performance.

2. Increase Memory Allocation

If query optimization is not sufficient, consider increasing the memory limit. This can be done by adjusting the query.max-memory and query.max-memory-per-node settings in the config.properties file of your Presto installation. For example:

query.max-memory=50GBquery.max-memory-per-node=5GB

After making changes, restart the Presto server to apply the new settings.

3. Monitor and Adjust Resource Usage

Use Presto's resource groups to manage and monitor resource usage effectively. This can help in identifying queries that frequently exceed memory limits and adjusting their resource allocations accordingly.

Conclusion

Encountering the QUERY_EXCEEDED_MEMORY_LIMIT error in Presto can be challenging, but with the right approach, it can be resolved. By optimizing queries and adjusting memory settings, you can ensure efficient query execution and maintain system stability. For more detailed guidance, refer to the Presto Memory Management Documentation.