2.1.6. Device Data Item: Memory Usage Options

The Device tab in the Data Item dialog box provides Just-In-Time as an additional memory usage option.

Memory options for instantiated points perform as follows

  • Delay load
  • Just-In-Time
  • Standard Memory Load

Delay Load

Delay loadis available in point configuration to help conserve memory.

The point is not loaded into memory in the Point Manager or Devcom at project startup. Rather, the point is loaded into memory only when it is demanded by an application. When the point ceases to be demanded it will be unloaded from memory in the Point Manager and Devcom.

Class: Data item configuration
Instantiation: Point properties result.
Benefits and disadvantages: Delay Load
  1. Class: Data item Configuration

When Delay Load is checked in a Data Item dialog box

  • Just-In-Time is disabled.
  • A scan rate is required.
  1. Instantiation: Point Properties Result

Delay Load is read/write in the object's Point Properties dialog box, whether or not it is checked in the Data Item dialog box.

  1. Benefits and Disadvantages: Delay Load

Delay Load benefits and disadvantages are the same whether the point is included in an instantiated object or is created in the project's Workbench. They are as follows.

Benefits Disadvantages Non-Supported Functions
  • Loaded when needed
  • No memory usage until point is loaded
  • Written to point database
  • Available in point list
  • Definition can be modified
  • Slower access
  • Configuration updates can be lengthy on larger systems
  • Trigger settings and Alarm options are not available
  • Trend buffering
  • Alarming
  • Cannot be used within another point's configuration, e.g. Safety point, Trigger, Availability Trigger point, etc.
  • Cannot be used in a calculation point equation

Just-In-Time

When Just-In-Time (JIT) is checked, data item instantiated point configuration is created by the Point Manager when an application requests it.

When the application is done, the data item is removed from the Point Manager. It is not written to the point database.

JIT Data Items can be used in:

  • CimView,
  • Point Control Panel,
  • Trending, and
  • Scripting.
Important: Change approvalis not supported with Just-In-Time points.
A Class: Data item configuration
B Instantiation: Point properties result.
C Benefits and disadvantages: Just-In-Time
  1. Class: Data Item Configuration

When Just-In-Time is checked:

  • Delay Load is disabled.
  • A scan rate is required.
  1. Instantiation: Point Manager Result

An instantiated object does not list a point for the Just-In-Time data item in the Workbench.

Example

The data item VLVBP in a class TANKR was configured to be a Just-In-Time point. It is not included in the instantiated point list when an object is created from the class.

  1. Benefits and Disadvantages: Just-in-Time

Just-In-Time benefits and disadvantages are as follows.

Benefits Disadvantages Non-supported Functions
  • Created on demand when needed
  • No memory usage until point is created
  • Project uses less disk space
  • Point database is reduced
  • Not available in point lists
  • Slowest access
  • Device points only
  • Does not reside in point database
  • Definition cannot be modified
  • Exclusive to classes
  • Trigger settings and Alarm options are not available
Note: Are not recommended for points that are accessed often.
  • Trend buffering
  • Alarming
  • Attribute set
  • Analog deadband
  • Cannot be used within another point's configuration, e.g. Safety point, Trigger, Availability Trigger point, etc.
  • Cannot be used in a calculation point equation
  • Cannot use another point within its configuration, e.g. Safety point, Trigger, Availability Trigger point, etc.
  • Cannot be marked as an enterprise point.

Standard Memory Load

When Delay Load and Just-In-Time check boxes are clear in a Data Item dialog box, an instantiated point has standard memory usage.

Standard memory load benefits and disadvantages are the same whether the point is included in an instantiated object or is created in the project's Workbench. They are as follows.

Benefits Disadvantages Non-supported Functions
  • Accessible any time
  • Quick access
  • Written to point database
  • Available in point list
  • Definition can be modified
  • Uses memory in point database
  • Project uses more memory
  • Configuration updates can be lengthy on larger systems
None—all functions supported