Precedence Constraints and Error Paths in SSIS

Precedence Constraints:
The  Precedence Constraints are used only in the Control Flow level of Package and not in the Data Flow level.
Some Constraints are :

• Solid
• Dashed
• Fx

Solid Lines are represents logical AND Precedence,  meaning that task will run only when all are the constraints conditions are met.
Dashed Lines are Logical OR statements between tasks.
Fx is the functional Symbol shows that an SSIS expression has been embedded in the constraint for evaluation.

We can edit the Precedence Constraints by double clicking the constraints or by right clicking the constraint.

Error Paths: Two types of Error paths in the Data Flow Task.

• Data Paths
• Error Paths 

Data Paths:
It indicates the green connector that go from one component to another.
The Rows that have gone successfully through a component are output if the error output set to Ignore Failure.

Error Paths:
The Red connection between data flow component.
They  contain data row that fail in a component when the error rows set to be Redirected.

All the component does not use Error Paths in the Data Flow Task. For example Multicast Component only copies the data. It does not perform any operations on the data itself.

To use Error Paths you need to configure the error output . There are three options for handling errors.

• Setting the error Output to Fail, Transformation causes the data flow to fail if an error is encountered.
• Setting error output to Ignore Failure Option causes let the row continues out the normal green data paths, but the value that resulted in the error is changed to Null in the Out put.
• Setting the error output to row out the Red error path. This is only one way to handle the errors with separate component.