SQL/MX 2.x Installation and Management Guide (G06.24+, H06.03+)

Understanding and Planning SQL/MX Tables
HP NonStop SQL/MX Installation and Management Guide—523723-004
4-3
Avoid Putting Same-Named Catalogs on Multiple
Distributed Nodes
Avoid Putting Same-Named Catalogs on Multiple Distributed
Nodes
If you create catalogs with the same name on two or more nodes, each node can
access only the objects in the local catalog. You cannot join the tables or indexes in the
same-named catalogs on different nodes.
Understanding SQL/MX Table and File
Structures
A relational database consists of two structural levels, the logical and the physical:
•
The logical level includes the tables and views you access directly through SQL
statements. When you request an operation on the database or a display of its
contents, you work with the database at the logical level.
•
The physical level underlies the logical level and is composed of physical files on
disks.
Each SQL/MX table and index, and each partition of a table or index, is implemented
as a pair of Guardian physical files representing:
•
A data fork, where the user data resides
•
A resource fork, where the runtime metadata resides
If a table or index is not partitioned, then it has just one data fork and one resource
fork.
Table and index files are managed by the SQL/MX file system and are accessed
implicitly through the DP2 disk process. When a table or index is dropped, both its data
fork and resource fork are also dropped.
The data you insert into tables and views is stored in these underlying files. Tables and
indexes are associated with their corresponding physical files through entries in the
system metadata. Views are associated with physical files through their underlying
tables.
When you create a table, you establish the characteristics of the underlying file by
specifying them as parameters in the CREATE TABLE statement. That is, you create
the file implicitly through this statement rather than directly through an explicit
file-creation statement.
Data transfers to and from the files are done in terms of logical records and key fields
within those records. Each file has a unique clustering key associated with it, which
contains a unique value used to order and identify records in the file.
SQL/MX tables use the key-sequenced file structure. Other table and file structure
types are not supported for NonStop SQL/MX.
Types of Keys Used in SQL/MX Tables and Indexes on page 4-4 describes the key
types used with SQL/MX tables and indexes. The Key-Sequenced File Structure on