Reload Analyzer Manual

Tandem Reload Analyzer Manual Page 18 of 42
Figure 1-1. Key-Sequenced File Structure
Each data block contains a header plus one or more data records, depending on the
record size and data block size. For each data block, an index block entry contains the
value of the primary-key field for the first record in the data block and the address of
that data block.
The data blocks in Figure 1-1 have a certain percentage of empty space or slack.
When you load data into a key-sequenced file, you can specify how much slack (empty
space for future growth) is needed.
When a new record is inserted into a key-sequenced file, the position of the record is
determined by the value of its primary-key field. If the block where the new record will
be inserted is full, the block splits. This means that the disk process creates a new
data block, moves part of the data from the old block into the new block, and gives the
index block a pointer to the new data block. Block splits can be costly because they
consume CPU (central processing unit) cycles and increase the time needed to
complete the input/output (I/O) requests.