Writer scaling properties#

Writer scaling allows Trino to dynamically scale out the number of writer tasks rather than allocating a fixed number of tasks. Additional tasks are added when the average amount of physical data per writer is above a minimum threshold, but only if the query is bottlenecked on writing.

Writer scaling is useful with connectors like Hive that produce one or more files per writer – reducing the number of writers results in a larger average file size. However, writer scaling can have a small impact on query wall time due to the decreased writer parallelism while the writer count ramps up to match the needs of the query.

All properties described in this page are defined as follows, depending on the deployment type:

  • Kubernetes: In the additionalProperties section of the the top-level coordinator and worker nodes in the values.yaml file.

  • Starburst Admin: In the files/coordinator/config.properties.j2 and files/worker/config.properties.j2 files.


  • Type: boolean

  • Default value: true

  • Session property: scale_writers

Enable writer scaling by dynamically increasing the number of writer tasks on the cluster.


  • Type: boolean

  • Default value: true

  • Session property: task_scale_writers_enabled

Enable scaling the number of concurrent writers within a task. The maximum writer count per task for scaling is task.scale-writers.max-writer-count. Additional writers are added only when the average amount of uncompressed data processed per writer is above the minimum threshold of writer-scaling-min-data-processed and query is bottlenecked on writing.


  • Type: integer

  • Default value: The number of physical CPUs of the node with a maximum of 32

Maximum number of concurrent writers per task up to which the task can be scaled when task.scale-writers.enabled is set. Increasing this value may improve the performance of writes when the query is bottlenecked on writing. Setting this too high may cause the cluster to become overloaded due to excessive resource utilization.


Deprecated and replaced by writer-scaling-min-data-processed.


  • Type: data size

  • Default value: 100MB

  • Session property: writer_scaling_min_data_processed

The minimum amount of uncompressed data that must be processed by a writer before another writer can be added.