Introduction to Data Management

Managing Records With ENSCRIBE
15873 Tandem Computers Incorporated 4-3
Figure 4-1. Using Key Values to Locate Records
S8020-015
In a key-sequenced file, only one record
can have the primary-key value JONES, J. A.
in the NAME field.
JONES, J. A. DAYTON, OHIO CENTRAL
MOORE, Q. A. LOS ANGELES, CA WESTERN
SMITH, S. A. CHICAGO, IL CENTRAL
Two or more records, however, can have
the value CENTRAL in their REGION
alternate-key fields.
Partitioning allows you to increase concurrent access to records, because the records
can be accessed in an overlapped way. Partitioning also enhances the management of
locks that apply to your data, because the maximum number of locks allowed applies
to individual partitions, not to whole files.
File partitioning, however, remains transparent to your application programs; your
programs request access to the files by file name, not by partition. ENSCRIBE and the
GUARDIAN 90 operating system handle the physical partition access implicitly.
Audited Files In systems with the Transaction Monitoring Facility (TMF), any file can be designated
as an audited file. To help maintain database consistency, the DP2 disk process (on
behalf of TMF) audits all transactions involving such files. That is, TMF maintains
audit-trail images of the database changes imposed by those transactions. If
necessary, TMF can use the audit trails later to back out failed transactions or to
restore audited files that a system failure has rendered inconsistent.
TMF also uses a record locking mechanism to control concurrent access of audited
files. This feature ensures that none of a given transaction’s changes are visible to
other concurrent transactions until all the given transaction’s changes are either
committed or are aborted and backed out.