Index Management › Connecting Records to Indexed Sets › Connecting Members to Unsorted Indexed Sets

Connecting Members to Unsorted Indexed Sets

To connect new members to indexed sets with FIRST, LAST, NEXT, and PRIOR set order, CA IDMS/DB inserts a new index entry between existing index entries. When one SR8 record fills, CA IDMS/DB creates a new SR8 record; there is only one level of SR8 records in an unsorted index.

Once a request has been made to connect a member occurrence to an indexed set, CA IDMS/DB first checks whether other entries exist. If no other entries exist, CA IDMS/DB creates and stores the first SR8 record (containing the first entry) and connects it to the owner occurrence with next, prior, and owner pointers. The target page for the first SR8 record is the page of the owner of the indexed set occurrence (plus displacement, if any).

CA IDMS/DB Actions

If other entries do exist, CA IDMS/DB takes the following actions:

Step 1

Identifies the appropriate SR8 record and insertion point based on the set order, as follows:

• NEXT—The insertion point is physically after the index entry for the current SET occurrence.
• FIRST—The insertion point is physically the first index entry in the first SR8 record.
• PRIOR—The insertion point is physically before the index entry for the current SET occurrence.
• LAST—The insertion point is physically the last index entry in the last SR8 record.

  Note: SQL-defined unsorted indexed constraints have an internal order of LAST.

Step 2

Inserts the new entry into the index, as follows:

• If there is enough space in the target SR8 record for the new entry (that is, the insertion of this entry would not exceed the maximum allowable entries, and the target SR8's page has sufficient available space), CA IDMS/DB inserts the new entry into the target SR8 record.
• If there is not enough space in the target SR8 for the new entry, CA IDMS/DB inserts the new entry based on the location of the identified insertion point, as follows:
  • If the identified insertion point is physically first in the target SR8 record, CA IDMS/DB checks whether there is enough space in the prior SR8 record:
    • If there is enough space in the prior SR8 record, CA IDMS/DB inserts the new entry as the physically last entry in the prior SR8 record.
    • If there is not enough space in the prior SR8 record, CA IDMS/DB splits the target SR8 record.
  • If the insertion point is physically last in the target SR8 record, CA IDMS/DB checks whether there is enough space in the next SR8 record:
    • If there is enough space in the next SR8 record, CA IDMS/DB inserts the new entry in the next SR8 record.
    • If there is not enough space in the next SR8 record, CA IDMS/DB splits the target SR8 record.
  • If the insertion point is neither the physically first nor last in the target SR8 record, CA IDMS/DB checks whether there is enough space in the next SR8 record:
    • If there is enough space in the next SR8 record, CA IDMS/DB moves the last entry to the SR8 record
    • If there is not enough space in the next SR8 record, CA IDMS/DB splits the target SR8 record.

      Index Pointers for Split SR8s

When CA IDMS/DB splits an SR8 record (Record A) into two SR8 records (Records A and B), the entries relocated to Record B point to member occurrences that still contain index pointers pointing to Record A if index pointers are maintained for the set (index pointers are optional for system-owned indexes). If index pointers are maintained, splitting Record A causes CA IDMS/DB to set the orphan count in Record A equal to the number of entries moved to Record B.

Splitting an SR8 Record

The following diagram shows splitting an SR8 record to add a member occurrence to an indexed set with a set order of NEXT. (Note that, for simplicity, prior and owner pointers are not included in this figure.)