SQL/MP Installation and Management Guide

Understanding and Planning Database Tables
HP NonStop SQL/MP Installation and Management Guide—523353-004
3-8
Key-Sequenced File Structure
If you do not use an index, access occurs by primary or clustering key. Access can
begin with the first record in the file or can be requested for only a specified range of
records in the file.
Key-Sequenced Tree Structure
Key-sequenced files are physically organized as one or more bit-map blocks and a
B-tree structure of index blocks and data blocks. Bit-map blocks within a structured file
organize the file’s free space.
Figure 3-1 on page 3-8 illustrates a sample tree structure for a key-sequenced file.
Figure 3-1. Key-Sequenced B-Tree Structure
Saved
for future
insertions
First (Highest)-Level Index Block
Second-Level Index Block
Data Blocks
Second-Level Index Block
MOLLY
MOLLY NATE
Data Record
Primary Key
Legend
1
2
VST002.vsd
Variable-length
physical records
OLGA RUSTY Empty
STEVE
ULENA Empty
Empty
AMY
BETTY
Empty
CAROL CHRIS Empty
LOUISE MILLY Empty
OLGA
STEVE
0
CAROL LOUISE
0 MOLLY VINCE
NATE is alphabetically greater than MOLLY but less than VINCE.
Go to the second-level index block that begins with MOLLY.
1
NATE is alphabetically greater than MOLLY but less than OLGA.
Go to the data block that begins with MOLLY.
2