1 Topics in Database Administration u What is database administration? u What are the tasks involved in establishing, creating, implementing and maintaining.

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Topics in Database Administration

What is database administration?

What are the tasks involved in establishing, creating, implementing and maintaining a database?

How is the quality of data addressed?

What are the tasks involved in: Database transaction integrity? Database backup/recovery? Database security? DBMS efficiency?

What is database administration?

Category Data Administration Database Administration

Definition Function responsible for the overall management of data resources.

Function responsible for the technical viability of the database and database management system.

Scope Broad: organization-wide. Long term orientation.

Narrow: technical application. Daily operations.

Major Tasks

Sets policies and standards. Coordinates and manages database design.

Enforces policies and procedures. Chooses and maintains technology.

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Tasks in “data” administration

Planning. Assist in the development of the IS architecture. Develop enterprise data model. Assist in database design for application development.

Policies and procedures. Establish metadata. Assesses and controls the quality of the data. Establish policies towards data ownership.

Internal marketing. Explain the concept of data as a shared resource. Resolve conflicts between organizational areas.

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More detail: Data Resource Management Tasks

Assess organizational data strategy.

Evaluate data level of data integration.

Evaluate quality of data.

Create and maintain metadata.

Create and maintain data models.

Identify stakeholders and ensure ongoing participation in data management.

Evaluate privacy of data. Determine ethical use of data collection and access.

Make effective use of data resources through business intelligence capabilities.

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Tasks in “database” administration

Planning. Guide the selection of hardware and DBMS software. Choose appropriate tool set for database administration,

development and maintenance.

Procedures and policies. Establish security policies.

Access. Update.

Establish application development policies. Use of views. Use of indexes.

Establish backup and recovery policies. Enforce policies.

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More detail: Technical Management Tasks

Install and update the DBMS.

Create the database(s). Establish tablespace.

Create users.

Manage data dictionary.

Populate the database(s).

Ensure data integrity. Triggers and stored procedures.

Referential integrity.

Additional data constructs implemented through SQL.

Perform data backup and recovery.

Monitor and tune performance.

Data Administrator Database Administrator

Education

Experience

Skills

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Three of the critical technical tasks of a DBA

Database backup and recovery. Anticipating the event of a database failure. Establishing & enforcing database backup & recovery

procedures.

Database security and integrity. Defining security requirements based on data and

application needs. Establishing and enforcing security procedures. Establishing and enforcing data integrity procedures.

DBMS optimization. Tracking current response time. Modifying DBMS parameters to improve response time.

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Database backup and recovery

What is backup and recovery? Backup: A method of storing data from a database in a

format that can be used to rebuild the database if necessary.

Recovery: Mechanisms for restoring a database quickly and accurately after loss or damage.

Why have backup and recovery? Human error. Hardware failure. Incorrect or invalid data. Program errors. Viruses. Natural catastrophes.

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Backup and recovery are based on transactions

A transaction is one or more database actions (SQL statements) that are treated as a single unit of work. If the transaction is successful, then the transaction is committed. If the transaction is not successful, then the transaction is rolled

back or aborted.

Order_tbl

PK OrderID

OrderDateFK1 CustomerID BillingCode

OrderLine_tbl

PK,FK1 OrderIDPK,FK2 ProductID

Quantity Price

Product_tbl

PK ProductID

Name Description QOH Cost

Customer_tbl

PK CustomerID

Name Address Zip Phone

contains

is placed

by

is for

Imagine a database with this structure

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Accepting an order for a product

INSERT INTO orderline_tbl VALUES (123,6812,10, 34.99);

UPDATE product_tblSET qoh = qoh - 10WHERE prod_no = 6812;

INSERT INTO order_tbl VALUES (123,’27-apr-06’, 765, ‘net30’);

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DBMS’s have methods to control transactions

Databases that support transactions provide specific commands for starting, committing, and rolling back transactions. Begin transaction.

End transaction.

Commit.

Rollback.

Autocommit.

Transaction throughput: The number of transactions processed per time interval. This is a measure of transaction processing performance.

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Transactions have properties

Atomicity: A transaction is an indivisible unit of work. Almost all languages that interface with a DBMS have a way to

signify the start and end of a transaction. Within the start and end are one or more SQL commands.

Consistency: The transaction moves a database from one state of consistency, through inconsistency to another state of consistency.

Isolation: A transaction executes in isolation from other transactions. This is also referred to as the “serializability” of transactions. A transaction can affect another transaction, so the transaction

must complete as though it is isolated in order to be accurate.

Durability: Once a transaction is committed, its effects on the database are durable, or permanent. No subsequent actions or failures to the database can cause that transaction to be lost.

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Transaction boundary decision

Division of work into transactions.

Objectives: Minimize transaction duration. Ensure transaction isolation.

Constraint: enforcement of important integrity constraints.

Transaction example

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Transaction boundary choices.

One transaction for the entire form?

One transaction for the main form and one transaction for all subform records?

One transaction for the main form and separate transactions for each subform record?

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Backup is conducted in 3 processes

Backup: A DBMS software utility provides a way to do a complete, full or incremental backup of the database in a consistent state. Complete: entire database. Full: all rows of specified tables. Incremental: rows that have changed since the last full backup.

Journalize: A DBMS software utility provides an audit trail of changes to the database. Transaction log: contains all data used to process changes against the

database. Database change log: contains a before-image and an after-image of

each row modified by a database transaction.

Checkpoint: A DBMS software utility that periodically suspends all transaction processing and synchronizes files within the database. Some databases, such as Oracle, do not actually halt processing. They

simply write checkpoint information to files.

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Recovery methods

A DBMS has a utility to recover the database. Usually referred to as the Recovery Manager.

The method of recovery depends on the type of failure.

Recovery Manager usually has the following options: Switch: Switches to a replica of the database on a different

storage device. Requires that a mirror image of the database is stored. Can be expensive. Assumption is a storage failure, not a failure in

transaction integrity, occurred. Restore/Rerun: Reprocesses the transactions for a given

time period against a correct version of the database. Assumption is that a failure in transaction integrity has

occurred. Can be very time-consuming.

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Two common methods of restore/rerun

Backward recovery. Also called “rollback” recovery. Used to undo unwanted changes to the database. Imagine that the current database is inaccurate. Before-images are applied to the current database to

return it to a prior state of consistency. Used to back out changes that are unwanted.

Forward recovery. Also called “rollforward” recovery. Used to recover accurate transactions and apply them to the database. Imagine that the current database is inaccurate. This

database must be replaced with a prior, consistent version of the database before forward recovery can begin.

After-images are applied to a past version of the database. Does not require that all transactions are applied - just takes the most recent after-images.

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Issues in database backup and recovery

Cost. Media. Computer overhead (processor, memory, disk) to create

journalizing files, control files, checkpoint files, etc. Personnel to supervise and tune.

Time. Can result in regularly scheduled downtime. Can make the system slower.

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Potential problems with shared databases

Concurrency control is the process of managing concurrent operations against a database in order to maintain data integrity.

Potential problems with shared databases are: Lost Update. Uncommitted Dependency. “Dirty Read” Incorrect Summary.

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Lost update

Transaction A Time Transaction B

Read SR (10) T1 T2 Read SR (10) If SR > 0 then SR = SR -1

T3

T4 If SR > 0 then SR = SR -1

Write SR (9) T5 T6 Write SR (9)

SR: Seats Remaining

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Uncommitted dependency or “dirty read”

Transaction A Time Transaction B

Read SR (10) T1 SR = SR - 1 T2 Write SR (9) T3 T4 Read SR (9) Rollback T5

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Incorrect summary

Transaction A Time Transaction B Read SR1 (10) T1 SR1 = SR1 - 1 T2 Write SR1 (9) T3 T4 Read SR1 (9) T5 Sum = Sum + SR1 T6 Read SR2 (5) T7 Sum = Sum + SR2 Read SR2 (5) T8 SR2 = SR2 - 1 T9 Write SR2 (4) T10

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Methods of concurrency control

Scheduler. The scheduler establishes the order in which the operations within concurrent transactions are executed. The scheduler interleaves the execution of database

operations to ensure serializability. Some schedulers have the ability to analyze transaction

content.

Locking: Fundamental tool of concurrency control.

Obtain lock before accessing an item.

Wait if a conflicting lock is held. Shared lock: conflicts with exclusive locks Exclusive lock: conflicts with all other kinds of locks

Concurrency control manager maintains the lock table

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More about locking

Locking. A lock guarantees exclusive use of a data item to a current transaction. Locking can be performed programmatically or left to the

DBMS. Granularity of locking depends on the DBMS.

Database level. Table level. Page level. Row level. Column level.

Can have shared or exclusive locks.

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Problem in locking

Deadlock: An impasse that occurs when two or more transactions have locked a common resource and each is waiting for the other to finish.

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Database security

Database Security: Protection of the data against accidental or intentional loss, destruction, or misuse. Threats to database security include the list below.

Accidental losses attributable to: Human error. Software failure. Hardware failure.

Theft and fraud.

Improper data access: Loss of privacy (personal data). Loss of confidentiality (corporate data).

Loss of data integrity.

Loss of availability.

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DBMS security features

Views (frequently referred to as subschemas).

Authorization rules. Controls incorporated in the DBMS. Restrict access to specific data. Restrict actions that can be taken.

User-defined procedures. Trigger an authorization procedure which asks additional

identification questions. Written in a standard programming language or proprietary

language.

Encryption.

Authentication schemes. Biometric devices.

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Oracle’s approach to security

Multi-user database systems, such as Oracle, include security features that control how a database is accessed and used. For example, security mechanisms: Prevent unauthorized database access. Prevent unauthorized access to schema objects. Control system resource usage (such as CPU time or disk

usage). Audit user actions.

Associated with each database user is a schema. A schema is a logical collection of database objects

(tables, views, sequences, synonyms, indexes, clusters, procedures, functions, packages, and database links).

By default, each database user creates and has access to all objects in the corresponding schema.

Oracle’s security mechanisms The Oracle server provides discretionary access control, which is

a means of restricting access to information based on privileges. The appropriate privilege must be assigned to a user in order for that user to

access a schema object. Appropriately privileged users can grant other users privileges at their discretion;

for this reason, this type of security is called "discretionary".

SQL statements used for security

SQL Statement Action

CREATE USER Allows the DBA to create a new user.

GRANT Allows the user to give other users privilegesto access the user's objects.

CREATE ROLE Allows the DBA to create a collection ofprivileges that can be assigned as a group.

ALTER USER Allows users to change their passwords. Canalso be used to change other attributes of auser.

REVOKE Removes privileges on an object from a user,users, or role.

SQL Statements Used for Data Integrity

SQL Statement Description

Create Domain Create custom data types with predefined CHECK constraints.

Create Assertion Create constraints involving multiple tables and calculations. Similar to CHECK constraints, but allows access to multiple tables through a SELECT statement.

Triggers and Stored Procedures

Discussed previously. Programmer can create customized integrity check through proprietary procedural language. PL/SQL for Oracle.

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DBMS query optimization

DBMS’s are differentiated by their query optimizers.

A query optimizer is a component of a DBMS.

You do not have the choice of how queries are implemented on the physical database, the query optimizer assumes this responsibility.

You can sometimes “help” and thus possibly improve the optimization process.

Query translation process

Syntax and semanticanalysis

Query transformation

Access planevaluation

Access planinterpretation

Code generation

Parsed query

Relational algebra query

AccessPlan

AccessPlan

Query

Query results Machine code

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Query optimizer methods

Rule based. Looks at syntax. Parses query and executes in the order written according to the

rules pre-established by the person who wrote the query optimizer.

Cost based. Looks at syntax. Looks at statistical data about the database. Parses query and executes based on the written and the

information about the current and historical data of the database.

Choose. Uses the rule based method for tables which have not been

used/analyzed in the past. Uses the cost based method for tables which have been

previously analyzed.

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Helping the query optimizer

Know which type of optimizer is used by the DBMS.

Order the query in a way that eliminates more rows with the first “where” condition.

Provide comments or suggestions.

Use joins instead of nested or correlated sub-queries.

Use single table conditions instead of joins.

Use queries that perform grouping with aggregate calculations only when really necessary.

Avoid using the “<>” or not equal condition.

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Becoming a DBA

Experience. Application programming with a database. Some DBA tasks. Systems programming with a database.

Education. Training classes with a specific DBMS. For example, Oracle offers a ten-class sequence for

DBA’s. Master’s degree?

Certification. Specific to DBMS. Offered by DBMS vendor. Formal programs offered for Oracle and SQL Server;

informal programs for other DBMS types.