How DAC Determines the Order of Task Execution within an Execution Plan

How DAC Determines the Order of Task Execution within an Execution

Plan

An execution plan is a collection of subject areas and a unique collection of tasks.

 A task can have prerequisite tasks that need to be executed before its own execution.

DAC determines the order of tasks based on the following considerations:

 A task's source and target table

The dependency algorithm first looks at a task's source and target table.

For example, suppose table A is populated by task T1 by reading from table B, and table B is populated by task T2 by reading from table C. The algorithm would determine task T2 should be executed before T1.

The dependency algorithm next considers the following:

Task phase

An ETL process typically goes through several phases. An example of a typical

order in which phases are executed is as follows:

1. Extract Dimension

2. Extract Fact

3. Load Dimension

4. Load Fact and Load Hierarchy (executed in parallel)

5. Load Aggregate tables

6. Update Dimensions

A table's Truncate Always properties

The order of execution based on Truncate Always properties is as follows:

1. Insert

2. Upsert

3. Physical data source

4. Priority

DAC randomly organizes tasks that have the same property values. If some tasks

need to be executed in a particular order, you can create a task group that allows

you to specify an execution order.