Parallel Processing Factor (Environment setting)

Tools that honor the Parallel Processing Factor environment will divide and perform operations across multiple processes.

Many modern computers include multiple-core CPUs. Spreading a geoprocessing operation across multiple processes can speed up performance by taking advantage of more than one core. The performance benefit of parallel processing varies from tool to tool.

Usage notes

• The value of this environment determines the number of processes across which a tool spreads its operation. Those processes will be divided between hardware cores (processors) built into the machine. The number of hardware cores does not change based on this setting.
• Each tool that honors this environment has a built-in default for the number of processes given a particular machine. You can change this based on your data, operation, and available resources.
• If you specify a percent value (using the % symbol) then the number of processes used will be the specified percentage of the number of cores on the machine, rounded to the nearest integer. For example, on a 4-core machine:
  • Setting 50% means the operation will be spread over 2 processes (50% * 4 = 2).
  • Setting 66% means the operation will be spread over 3 processes (66% * 4 = 2.64 which rounds to 3).
  • Setting 100% means the operation will be spread over all 4 processes (100% * 4 = 4).

• Specifying more processes than your machine has cores may incur a performance penalty. This is because multiple processes will compete for resources on one core. To specify the Parallel Processing Factor in a way that avoids this competition you can either use a percent value less than 100% or a number of processes less than the number of cores on your machine.

  However, for cases where all your processes are I/O bound to a disk or to an enterprise database connection, you may get better performance by specifying more processes than you have cores. For example, the Add Rasters to Mosaic Dataset tool is I/O bound when the mosaic dataset is stored in an enterprise database. Also, the Build Overviews tool is primarily I/O bound to the disk. You can use more processes than your machine has cores by either specifying a percent value greater than 100% or a number of processes greater than the number of cores on your machine. For example, if you have a four-core machine, then specifying 8 or 200% will spread operations over eight processes.

Dialog syntax

Parallel Processing Factor—The number of processes across which a tool will spread its operation.

• blank (empty)—Let each tool determine how many processes to use. This is the default.
• 0—Do not spread operations across multiple processes.
• n—Use the specified number of processes.
• n%—Calculate the number of processes using the specified percentage: Number of processes = number of system cores * n / 100.

Scripting syntax

arcpy.env.parallelProcessingFactor = string

Parameters	Explanation
empty string (blank)	Let each tool determine how many processes to use. This is the default.
0	Do not spread operations across multiple processes.
n	Use the specified number of processes.
n%	Calculate the number of processes using the specified percentage: Number of processes = number of system cores * n / 100.

parallelProcessingFactor syntax

Script example

import arcpy

# Use half of the cores on the machine.
arcpy.env.parallelProcessingFactor = "50%"