Delete rules summary
The following list provides a summary of the delete rules.
- The DLET Call
- A DLET call issued against a concatenated segment (SOURCE=DATA/DATA,
DATA/KEY, KEY/DATA) is a DLET call against the logical child only.
A DLET call against a logical child that has been accessed from its logical parent is a request that the logical child be logically deleted.
In all other cases, a DLET call issued against a segment is a request for that segment to be physically deleted.
- Physical Deletion
- A physically deleted segment cannot be accessed from its physical path, however, one exception exists: If one of the physical parents of the physically deleted segment is a logical child that can be accessed from its logical parent, then the physically deleted segment is accessible from that logical child. The physically deleted segments is accessible because the physical dependents of the logical child are variable intersection data.
- Logical Deletion
- By definition, a logically deleted logical child cannot be accessed
from its logical parent. Unidirectional logical child segments are
assumed to be logically deleted.
By definition, a logical parent is considered logically deleted when all its logical children are physically deleted and all its physical children that are part of a physically paired set are physically deleted.
- Access Paths
- Neither physical nor logical deletion of a segment prevents access to the segment from its physical or logical children, or from the segment to its physical or logical parents. A physically deleted root segment can be accessed only from its physical or logical children.
- Propagation of Delete
- In bidirectional physical pairing, physical deletion of one of
the pair of logical children causes logical deletion of its paired
segment. Likewise, logical deletion of one causes physical deletion
of the other.
Physical deletion of a segment propagates logical deletion requests to its bidirectional logical children. Physical deletion of a segment propagates physical deletion requests to its physical children and to any index pointer segments for which it is the source segment.
- Delete Rules
- Further delete operations are governed by the following delete
rules:
- Logical Parent
- When RULES=P is specified, if the segment is not already logically
deleted, a DLET call against the segment or any of its physical parents
results in a DX status code. No segments are deleted. If a request
is made against the segment as a result of propagation across a logical
relationship, then the P rule works like the L rule.
When RULES=L is specified, either physical or logical deletion can occur first, and neither causes the other to occur.
When RULES=V is specified, either physical or logical deletion can occur first. If the segment is logically deleted as the result of a DLET call, then it is physically deleted also.
- Physical Parent of a Virtually Paired Logical Child
- RULES=P, L, or V is meaningless.
When RULES=B is specified and all physical children that are virtually paired logical children are logically deleted, the physical parent segment is physically deleted.
- Logical Child
- When RULES=P is specified, if the segment is not already logically
deleted, then a DLET call requesting physical deletion of the segment
or any of its physical parents results in a DX status code. No segments
are deleted. If a delete request is made against the segment as a
result of propagation across a logical relationship or if the segment
is one of a physically paired set, then the rule works like the L
rule.
When RULES=L is specified, either physical or logical deletion can occur first, and neither causes the other to occur.
When RULES=V is specified, either physical or logical deletion can occur first and either causes the other to occur. If this rule is used on only one segment of a physically paired set, it works like the L rule.
- Space Release
- Depending on the database organization, DASD space can or cannot
be reused when it is released. DASD space for a segment is released
when the following conditions are met:
- Space has been released for all physical dependents of the segment.
- The segment is physically deleted.
- If the segment is a logical child or a logical parent, then it is physically and logically deleted.
- If the segment is a dependent of a logical child (variable intersection data) and the DLET call was issued against a physical parent of the logical child, then the logical child is both physically and logically deleted.
- If the segment is a primary index pointer segment, the space is released for its target segment.