VSAM Control Area

What is VSAM Control Area?

A group of control intervals makes up a control area. Since the control intervals are grouped to form control area the way of filling the control area is similar to the way of filling records in control interval as discussed in detail in our previous paragraph. The number of control intervals per control area depends on how much space is reserved when the dataset is created. This is shown diagrammatically below:

Attributes in the index component

The index component has the following attributes as given below:

• index set
• sequence set

The index set lists the largest index within each control area and the sequence set lists the largest index within each control interval.

The records get allocated in Control Interval and Control area in the following manner:

• Check for enough free space within a control interval is made and if such a space is present then the new records gets added in that position.

• If the Check for enough free space within a control interval returns no enough free space within a control interval then a check for the presence of empty control interval within the same control area is made and if such a empty control interval within the same control area occurs the control interval split is made with the record from the control interval which is filled with records being moved to the empty control interval space.

• If in case of Check for enough free space within a control interval returns no enough free space within a control interval and also there is no empty control interval within the same control area then control area split is made and records gets moved to the new control area.

First Page: VSAM Control Interval and Control Area