# 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.

## scale-writers#

• Type: boolean

• Default value: true

Enable writer scaling by dynamically increasing the number of writer tasks on the cluster. This can be specified on a per-query basis using the scale_writers session property.

## task.scale-writers.enabled#

• Type: boolean

• Default value: true

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 physical data written per writer is above the minimum threshold of writer-min-size and query is bottlenecked on writing. This can be specified on a per-query basis using the task_scale_writers session property.

## task.scale-writers.max-writer-count#

• Type: integer

• Restrictions: Must be a power of two

• Default value: 8

Maximum number of concurrent writers per task upto 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.

## writer-min-size#

• Type: data size

• Default value: 32MB

The minimum amount of data that must be written by a writer task before another writer is eligible to be added. Each writer task may have multiple writers, controlled by task.writer-count, thus this value is effectively divided by the number of writers per task. This can be specified on a per-query basis using the writer_min_size session property.