Databases Reference
In-Depth Information
database and users begin to access the data. When using a new DBMS, users
will discover new methods of using data to facilitate their work tasks in ways
the DBA did not anticipate. The DBA may find it necessary to modify the
physical database design. In order to keep the DBMS working at near-optimal
performance, the DBA needs to add and remove search keys, change index
structures, and evolve the database. The DBA should monitor the DBMS
activity to detect inefficiencies and take corrective action by modifying the
physical data structures to reflect the new and unanticipated uses.
In many enterprises, DBMSs are accessed differently during different
phases of their business cycle. For example, the DBMS maintaining student
registration and grade information is accessed quite differently at the
beginning of a term, in the middle of a term, and at the end of a term. The
DBA should anticipate the changes in access during different processing
phases and may adjust physical access structures accordingly.
Most major DBMS vendors provide a variety of performance-monitoring
tools to assist the DBA in understanding how the DBMS is being used. Some
of these tools and utilities are able to suggest changes to the physical data-
base design and, with approval from the DBA, automatically implement
those changes. However, the self-organizing DBMS is still in the distant
future. Until then, the DBA will play a critical role in providing high perfor-
mance for modern DBMSs.
CONCLUSION
In order to develop a good initial physical database design, the DBA must
understand the anticipated workload of the DBMS, which includes the rela-
tive frequencies of queries and updates, as well as the properties of the var-
ious access methods and index structures available within the DBMS.
The DBA can use the four-phase procedure outlined in this article for
designing an initial physical database. However, the method should be
modified and extended appropriately to include any special data struc-
tures supported by the DBMS being used by the enterprise.
However, the DBA still is not finished after completing the initial physi-
cal database design. The DBA should monitor DBMS activity and modify
the physical design when new queries and transactions adversely affect
the DBMS performance.
Notes
1. Elmasri, R. and Navathe, S.
2nd ed., Reading, MA: Ad-
dison-Wesley, 1994. Contains chapters on record storage and primary file organizations,
index structures for files, and a short section on physical database design guidelines.
2. Ramakrishnan, R.
Fundamentals of Database Systems,
New York: WCB/McGraw-Hill, 1998. Con-
tains chapters on files, file organizations and indexes, tree-structured indexing, hash-
based indexing, and physical database design and tuning.
Database Management Systems,
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