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Choosing the right DB instance class - Amazon Aurora
When to use EBS-only instances

Choosing the right DB instance class

The right instance class depends on how your foreign table queries use memory, storage, and CPU. For details about each of these resources, see Resource management.

  • Memory: A foreign table query holds its working data (sorts, aggregations, and hash tables for joins) in memory, bounded by the aurora_analytics.query_mem setting (query_mem for short). The default value of query_mem scales with instance size, so a larger instance gives each query more memory automatically. When a query exceeds query_mem, it spills to local storage, which is slower. For more information, see Tuning query_mem for your workload.

  • Concurrency: Each concurrent foreign table query allocates memory up to query_mem, but actual usage depends on the query, and simple queries might use far less. When you size for concurrency, budget for peak memory rather than assuming every query uses the full query_mem. For more information, see Concurrency sizing.

  • Caching and spilling: The on-disk cache for Amazon S3 data and the temporary files that queries spill both use the instance's local storage. Local NVMe (available on d-type instances such as db.r8gd) is faster than Amazon EBS for both, so choose a class with local NVMe storage for production workloads that query foreign tables.

  • Workload isolation: Foreign table queries compete with the rest of the instance's traffic for CPU and memory. For workloads that query foreign tables heavily, run them on a dedicated reader instead. For more information, see Using a dedicated reader instance for analytics.

Start with a class that fits your workload and adjust from there, using these signals.

  • Rising AuroraAnalyticsMemoryUsage means overall memory pressure is growing. Scale up to a larger instance class, or lower query_mem to leave room for concurrency.

  • Rising AuroraAnalyticsDiskSpillSize means individual queries are exceeding query_mem and spilling to local storage. Scale up, or raise query_mem to give each query more room.

  • A falling AuroraAnalyticsCacheHitRatio means more of your working data is being re-read from Amazon S3. A larger instance class caches more of it locally.

  • High CPU while querying foreign tables means queries need more vCPUs.

To handle more concurrent queries, scale up for more memory headroom, or add a reader to spread the load.

For these metrics and how to monitor them, see Monitoring and troubleshooting.

When to use EBS-only instances

Instances without local NVMe storage (such as db.r8g and db.r8i) use Amazon EBS for caching. Use them for the following.

  • Workloads that are more cost-sensitive than performance-sensitive.

  • Light or ad hoc foreign table queries.

  • Development and testing environments.