Presto C++ Properties Reference

This section describes Presto C++ configuration properties.

The following is not a complete list of all configuration and session properties, and does not include any connector-specific catalog configuration properties. For information on catalog configuration properties, see Connectors.

Coordinator Properties

Set the following configuration properties for the Presto coordinator exactly as they are shown in this code block to enable the Presto coordinator’s use of Presto C++ workers.

native-execution-enabled=true
optimizer.optimize-hash-generation=false
regex-library=RE2J
use-alternative-function-signatures=true
experimental.table-writer-merge-operator-enabled=false

These Presto coordinator configuration properties are described here, in alphabetical order.

experimental.table-writer-merge-operator-enabled

• Type: boolean

• Default value: true

  Merge TableWriter output before sending to TableFinishOperator. This property must be set to false.

native-execution-enabled

• Type: boolean

• Default value: false

  This property is required when running Presto C++ workers because of underlying differences in behavior from Java workers.

optimizer.optimize-hash-generation

• Type: boolean

• Default value: true

  Set this property to false when running Presto C++ workers. Velox does not support optimized hash generation, instead using a HashTable with adaptive runtime optimizations that does not use extra hash fields.

regex-library

• Type: type

• Allowed values: RE2J

• Default value: JONI

  Only RE2J is currently supported by Velox.

use-alternative-function-signatures

• Type: boolean

• Default value: false

  Some aggregation functions use generic intermediate types which are not compatible with Velox aggregation function intermediate types. One example function is approx_distinct, whose intermediate type is VARBINARY. This property provides function signatures for built-in aggregation functions which are compatible with Velox.

Worker Properties

The configuration properties of Presto C++ workers are described here, in alphabetical order.

async-data-cache-enabled

• Type: boolean

• Default value: true

  In-memory cache.

query.max-memory-per-node

• Type: integer

• Default value: 4GB

  Max memory usage for each query.

query-memory-gb

• Type: integer

• Default value: 38

  Specifies the total amount of memory in GB that can be used for all queries on a worker node. Memory for system usage such as disk spilling and cache prefetch are not counted in it.

query-reserved-memory-gb

• Type: integer

• Default value: 4

  Specifies the total amount of memory in GB reserved for the queries on a worker node. A query can only allocate from this reserved space if 1) the non-reserved space in query-memory-gb is used up; and 2) the amount it tries to get is less than memory-pool-reserved-capacity.

runtime-metrics-collection-enabled

• Type: boolean

• Default value: false

  Enables collection of worker level metrics.

system-memory-gb

• Type: integer

• Default value: 40

  Memory allocation limit enforced via internal memory allocator. It consists of two parts: 1) Memory used by the queries as specified in query-memory-gb; 2) Memory used by the system, such as disk spilling and cache prefetch.

  Set system-memory-gb to the available machine memory of the deployment.

task.max-drivers-per-task

• Type: integer

• Default value: number of hardware CPUs

  Number of drivers to use per task. Defaults to hardware CPUs.