Changes Involving Multiple Blocks in the Sequence Set (Cont.)
Deletions.
A deletion from Block 2 causes underflow and consequent merging of Blocks 2 and 3.
After the merging, Block 3 is no longer needed in the sequence set.
The separator, CAM, that once distinguished between Blocks 2 and 3 must be removed from the index set, which causes an underflow.
The underflow forces a merging of index set nodes, bringing BO back down into a node with the AY separator.
Summary.
These two kinds of changes affect the tree's two structures:
The sequence set:
Record insertion and deletion always take place in the sequence set as if there are no index set at all.
The index set:
Index set operations are performed according to the rules for B-trees.
Perform the following changes in the index set after the following tasks happen in the sequence set:
Split.
A new separator must be inserted.
Merging.
A separator must be removed.
Redistribution.
The value of a separator must be changed.
