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

Connecting Members to Sorted Indexed Sets

Spawning

CA IDMS/DB organizes an index for sorted records into levels. When a top or intermediate SR8 record is full, CA IDMS/DB spawns a new level through the following steps:

1. CA IDMS/DB splits the SR8 record into two SR8 records.
2. CA IDMS/DB constructs a new higher-level SR8 record. This new full-size SR8 record contains only two entries. Each entry points to one of the SR8 records created by Step 1.

   CA IDMS/DB determines the target page of a new SR8 record, as follows:

   • If displacement has been specified and if the new record is a bottom-level SR8 record, the target page is the page of the owner of the indexed set occurrence plus displacement.
   • Otherwise, the target page is the page of the owner of the indexed set occurrence.

CA IDMS/DB repeats this process as the index expands. Indexes can have any number of intermediate levels. As CA IDMS/DB adds new entries, it splits SR8 records and spawns new levels of SR8 records. An entry on one level points to an SR8 record at a lower level; the bottom-level entries point to the indexed database records themselves.

Connecting New Members

To connect new members into a sorted index, CA IDMS/DB first identifies the appropriate insertion point of the new entry based on the symbolic key or db-key. If this is the first entry (and, therefore, the first SR8 record), CA IDMS/DB creates, stores and connects a new SR8 record to the owner occurrence. CA IDMS/DB determines the target page for the new SR8 record as described above.

If this is not the first entry, CA IDMS/DB identifies the insertion point of the new entry based on the symbolic key or db-key. Once the appropriate insertion point is identified, CA IDMS/DB inserts the new entry into the index, as follows:

• If there is space in the target SR8 record (that is, if insertion of this entry would not exceed maximum allowable entries and the target SR8 record's page has sufficient available space, CA IDMS/DB inserts the new entry in the target SR8 record.
• If space in the target SR8 record is insufficient for the new entry, CA IDMS/DB attempts to move a number of entries to a prior or next SR8 record if space is available. Otherwise, a split occurs which may cause spawning depending on the available space in the higher-level SR8 records.