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Pre-initialized capacity

EMR Serverless provides an optional feature that keeps driver and workers pre-initialized and ready to respond in seconds. This effectively creates a warm pool of workers for an application. This feature is called pre-initialized capacity. To configure this feature, you can set the initialCapacity parameter of an application to the number of workers you want to pre-initialize. With pre-initialized worker capacity, jobs start immediately. This is ideal when you want to implement iterative applications and time-sensitive jobs.

When you submit a job, if workers from initialCapacity are available, the job uses those resources to start its run. If those workers are already in use by other jobs, or if the job needs more resources than available from initialCapacity, then the application requests and gets additional workers, up to the maximum limits on resources set for the application. When a job finishes its run, it releases the workers that it used, and the number of resources available for the application returns to initialCapacity. An application maintains the initialCapacity of resources even after jobs finish their runs. The application releases excess resources beyond initialCapacity when the jobs no longer need them to run.

Pre-initialized capacity is available and ready to use when the application has started. The pre-initialized capacity becomes inactive when the application is stopped. An application moves to the STARTED state only if the requested pre-initialized capacity has been created and is ready to use. The whole time that the application is in the STARTED state, EMR Serverless keeps the pre-initialized capacity available for use or in use by jobs or interactive workloads. The feature restores capacity for released or failed containers. This maintains the number of workers that the InitialCapacity parameter specifies. The state of an application with no pre-initialized capacity can immediately change from CREATED to STARTED.

You can configure the application to release pre-initialized capacity if it isn't used for a certain period of time, with a default of 15 minutes. A stopped application starts automatically when you submit a new job. You can set these automatic start and stop configurations when you create the application, or you can change them when the application is in a CREATED or STOPPED state.

You can change the InitialCapacity counts, and specify compute configurations such as CPU, memory, and disk, for each worker. Because you can't make partial modifications, you should specify all compute configurations when you change values. You can only change configurations when the application is in the CREATED or STOPPED state.

Customizing pre-initialized capacity for Spark and Hive

You can further customize pre-initialized capacity for workloads that run on specific big data frameworks. For example, when a workload runs on Apache Spark, you can specify how many workers start as drivers and how many start as executors. Similarly, when you use Apache Hive, you can specify how many workers start as Hive drivers, and how many should run Tez tasks.

Configuring an application running Apache Hive with pre-initialized capacity

The following API request creates an application running Apache Hive based on Amazon EMR release emr-6.6.0. The application starts with 5 pre-initialized Hive drivers, each with 2 vCPU and 4 GB of memory, and 50 pre-initialized Tez task workers, each with 4 vCPU and 8 GB of memory. When Hive queries run on this application, they first use the pre-initialized workers and start executing immediately. If all of the pre-initialized workers are busy and more Hive jobs are submitted, the application can scale to a total of 400 vCPU and 1024 GB of memory. You can optionally omit capacity for either the DRIVER or the TEZ_TASK worker.

aws emr-serverless create-application \
  --type "HIVE" \
  --name my-application-name \
  --release-label emr-6.6.0 \
  --initial-capacity '{
    "DRIVER": {
        "workerCount": 5,
        "workerConfiguration": {
            "cpu": "2vCPU",
            "memory": "4GB"
        }
    },
    "TEZ_TASK": {
        "workerCount": 50,
        "workerConfiguration": {
            "cpu": "4vCPU",
            "memory": "8GB"
        }
    }
  }' \
  --maximum-capacity '{
    "cpu": "400vCPU",
    "memory": "1024GB"
  }'

Configuring an application running Apache Spark with pre-initialized capacity

The following API request creates an application that runs Apache Spark 3.2.0 based on Amazon EMR release 6.6.0. The application starts with 5 pre-initialized Spark drivers, each with 2 vCPU and 4 GB of memory, and 50 pre-initialized executors, each with 4 vCPU and 8 GB of memory. When Spark jobs run on this application, they first use the pre-initialized workers and start to execute immediately. If all of the pre-initialized workers are busy and more Spark jobs are submitted, the application can scale to a total of 400 vCPU and 1024 GB of memory. You can optionally omit capacity for either the DRIVER or the EXECUTOR.

aws emr-serverless create-application \
  --type "SPARK" \
  --name my-application-name \
  --release-label emr-6.6.0 \
  --initial-capacity '{
    "DRIVER": {
        "workerCount": 5,
        "workerConfiguration": {
            "cpu": "2vCPU",
            "memory": "4GB"
        }
    },
    "EXECUTOR": {
        "workerCount": 50,
        "workerConfiguration": {
            "cpu": "4vCPU",
            "memory": "8GB"
        }
    }
  }' \
  --maximum-capacity '{
    "cpu": "400vCPU",
    "memory": "1024GB"
  }'