• Full Name Full Name Comment goes here.
    Are you sure you want to
    Your message goes here
    Be the first to comment
    Be the first to like this
No Downloads

Views

Total Views
257
On Slideshare
0
From Embeds
0
Number of Embeds
0

Actions

Shares
Downloads
2
Comments
0
Likes
0

Embeds 0

No embeds

Report content

Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
    No notes for slide

Transcript

  • 1. David M. Kroenke Database Processing Chapter 9 Managing Multi-User Databases
  • 2. Multi-User Databases
    • Serving the needs of multiple users and multiple applications adds complexity in…
      • design,
      • development, and
      • migration (future updates)
  • 3. Multi-User Database Issues
    • Interdependency
      • Changes required by one user may impact others
    • Concurrency
      • People or applications may try to update the same information at the same time
  • 4. Multi-User Database Issues
    • Record Retention
      • When information should be discarded
    • Backup/Recovery
      • How to protect yourself from losing critical information
  • 5. Role of the Database Administrator
    • Organizations typically hire a database administrator (DBA) to handle the issues and complexities associated with multi-user databases.
    • A DBA facilitates the development and use of one or more databases.
  • 6. Data Administrator versus Database Administrator
    • Data Administrator
      • Handle the database functions and responsibilities for the entire organization.
    • Database Administrator (DBA)
      • Handle the functions associated with a specific database, including those applications served by the database.
  • 7. The Characteristics of a DBA
    • Technical
      • The DBA is responsible for the performance and maintenance of one or more databases.
    • Diplomatic
      • The DBA must coordinate the efforts, requirements, and sometimes conflicting goals of various user groups to develop community-wide solutions.
  • 8. Technical Skills of the DBA
    • Managing the database structure
    • Controlling concurrent processing
    • Managing processing rights and responsibilities
    • Developing database security
    • Providing database recovery
    • Managing the database management system (DBMS)
    • Maintaining the data repository
  • 9. Managing the Database Structure
    • Managing the database structure includes configuration control and documentation regarding:
      • The allocation of space
      • Table creation
      • Indices creation
      • Storage procedures
      • Trigger creation
  • 10. Configuration Control
    • Post-implementation changes
    • Procedures & Policies
    • Address unanticipated problems
  • 11. The Need for Documentation
    • Crucial when trying to understand problems
    • Backups and Restores
    • Documentation provides the “paper” trail for changes
  • 12. Documentation
    • All structural changes must be carefully documented with the following:
      • Reason for change
      • Who made the changes
      • Specifically what was changed
      • How and when the changes were implemented
      • How were the changes tested and what were the results
  • 13. Controlling Concurrency Processing
    • Concurrency control ensures that one user’s actions do not adversely impact another user’s actions
    • At the core of concurrency is accessibility.
  • 14. Aspects of Concurrency Control
    • Rollback/Commit : Ensuring all actions are successful before posting to the database
    • Multitasking : Simultaneously serving multiple users
    • Lost Updates : When one user’s action overwrites another user’s request
  • 15. Rollback/Commit
    • Involve logical units of work (LUW) .
    • Commit when entire LUW successful.
    • Rollback if any part of LUW is unsuccessful
  • 16. Lost Update Problem
    • When two or more users are attempting to update the same piece of data at the same time.
    • Resource locking scenarios are designed to address this problem
  • 17. Resource Locking
    • A resource lock prevents a user from reading and/or writing to a piece of data
    • The size of the piece of data (e.g., database, table, row) is termed the lock granularity
  • 18. Types of Resource Locks
    • Implicit versus Explicit
    • Exclusive versus Shared
  • 19. Two-Phased Resource Locking
    • Two-phased locking , whereby locks are obtained as they are needed
      • A growing phase , whereby the transaction continues to request additional locks
      • A shrinking phase , whereby the transaction begins to release the locks
  • 20. Deadlocks
    • When two transactions are waiting on one another to release resources.
  • 21. Avoiding Deadlocks
    • Strategy 1:
      • Wait until all resources are available, then lock them all before beginning
    • Strategy 2:
      • Establish and use clear locking orders/sequences
    • Strategy 3:
      • Once detected, the DBMS will rollback one transaction
  • 22. Resource Locking Strategies
    • Optimistic Locking
      • Read data
      • Process transaction
      • Issue update
      • Look for conflict
      • If conflict occurred, rollback and repeat or else commit
    • Pessimistic Locking
      • Lock required resources
      • Read data
      • Process transaction
      • Issue update
      • Release locks
  • 23. Providing Database Recovery
    • Common causes of database failures…
      • Hardware failures
      • Programming bugs
      • Human errors/mistakes
      • Malicious actions
    • Since these issues are impossible to completely avoid, recovery procedures are essential
  • 24. Database Recovery Characteristics
    • Continuing business operations (Fall-back procedures/Continuity planning)
    • Restore from backup
    • Replay database activities since backup was originally made
  • 25. Fall-back Procedures/ Continuity Planning
    • The business will continue to operate even when the database is inaccessible
    • The fall-back procedure defines how the organization will continue operations
    • Careful attention must be paid to…
      • saving essential data
      • continuing to provide quality service
  • 26. Restoring from Backup
    • In the event that the system must be rebuilt or reloaded, the database is restored from the last full backup.
    • Since it is inevitable that activities occurred since the last full backup was made, subsequent activities must be replayed/restored.
  • 27. Recovery via Reprocessing
    • This is a brute-force technique.
    • Simply re-type all activities since the backup was performed.
      • Costly (extra time)
      • Risky (human error)
  • 28. Recovery via Rollback/Rollforward
    • Most database management systems provide a mechanism to record activities into a log file.
  • 29. Rollforward
    • Activities recorded in the log files may be replayed. In doing so, all activities are re-applied to the database.
    • Use to resynchronize restored database data.
  • 30. Rollback
    • Since log files save activities in sequence order, can undo activities in reverse order than when they were originally executed.
    • Used to correct/undo erroneous or malicious transaction(s).
  • 31. Database Security
    • Database security strives to ensure…
      • Only authorized users perform authorized activities at authorized times
  • 32. Managing Processing Rights and Responsibilities
    • Processing rights define who is permitted to do what, when
    • The individuals performing these activities have full responsibility for the implications of their actions
    • Individuals are identified by a username and a password
  • 33. Granting of Processing Rights
    • Database users are known as an individual and as a member of one or more role
    • Access and processing rights/privileges may be granted to an individual and/or a role
    • Users possess the compilation of rights granted to the individual and all the roles for which they are members
  • 34. Granting Privileges
  • 35. Managing the Database Management System (DBMS)
    • In addition to controlling and maintaining the users and the data, the DBA must also maintain and monitor the DBMS itself.
      • Performance statistics (performance tuning / optimizing)
      • System and data integrity
      • Establishing, configuring, and maintaining database features and utilities
  • 36. Maintaining the Data Repository
    • The data repository contains metadata. Metadata is data about data.
    • The data repository specifies the name, type, size, format, structure, definitions, and relationships among the data. They also contain the details about applications, users, add-on products, etc.
  • 37. Types of Data Repositories
    • Active data repository
      • The development and management tools automatically maintain and upkeep the metadata.
    • Passive data repository
      • People manually maintain and upkeep the metadata
  • 38. Consistent Transactions
    • Consistent transactions are often referred to by the acronym ACID
          • Atomic
          • Consistent
          • Isolated
          • Durable
  • 39. ACID: Atomic
    • A transaction consists of a series of steps. Each step must be successful for the transaction to be saved.
    • This ensures that the transaction completes everything it intended to do before saving the changes.
  • 40. ACID: Consistent
    • No other transactions are permitted on the records until the current statement finishes
    • This ensures that the transaction integrity has statement level consistence among all records
  • 41. ACID: Isolation
    • Within multi-user environments, different transactions may be operating on the same data. As such, the sequencing of uncommitted updates, rollbacks, and commits continuously change the data content.
    • The 1992 ANSI SQL standards define four isolation levels and specify respective issues.
  • 42. Summary of Isolation Levels
  • 43. ACID: Durable
    • Once committed, durable transactions are saved to the data permanently
  • 44. Set-at-a-Time Versus Row-at-a-Time
    • SQL statements act as filters for the entire data set.
    • A cursor may be defined within a SQL statement to point to a particular record.
    • Several types of cursors have been defined. The cursor type defines how the cursor behaves.
  • 45. Types of Cursors