Transaction Management and Concurrency Control

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  1. A logical unit of work that must be entirely completed or entirely aborted.
  2. A successful transaction changes the database from one ______ to another.
    consistent state
  3. One in which all data integrity constraints are satisfied.
    consistent database state
  4. Any action that reads from and/or writes to a database
  5. To ensure consistency of the database, every transaction must begin with the database in a _______.
    known consistent state
  6. The equivalent of a single SQL statement in an application program or transaction.
    database request
  7. (T/F) Not all transactions update the database.
  8. (T/F) A transaction may consist of a single SQL statement or a collection of related SQL statements.
  9. (T/F) Improper or incomplete transactions can have a devastating effect on database integrity.
  10. Transaction Properties
    • Atomicity
    • Consistency
    • Isolation
    • Durability
    • Serializability
  11. All operations of a transaction must be completed; if not, the transaction is aborted.
  12. Indicates the permanence of the database’s consistent state.
  13. Data used during the execution of a transaction cannot be used by a second transaction until the first one is completed.
  14. Once transactions are done, they cannot be undone or lost.
  15. Ensures that the schedule for the concurrent execution of the transactions yields consistent results.
  16. Defined standards that govern SQL database transactions.
    American National Standards Institute (ANSI)
  17. Transaction support is provided by two SQL statements:
    • COMMIT
  18. Transaction sequence must continue until
    • A COMMIT statement is reached
    • A ROLLBACK statement is reached
    • The end of a program is reached
    • The program is abnormally terminated
  19. Keeps track of all transactions that update the database.
    Transaction Log
  20. The coordination of the simultaneous execution of transactions in a multiuser database system.
    concurrency control
  21. Objective of concurrency control
    Ensure the serializability of transactions in amultiuser database environment
  22. The three main problems of concurrency control:
    • Lost updates
    • Uncommitted data
    • Inconsistent retrievals
  23. Occurs when two concurrent transactions are updating the same data element and one of the updates is lost (overwritten by the other transaction).
    Lost update
  24. Occurs when two transactions are executed concurrently and the first transaction is rolled back after the second transaction has already accessed the uncommitted data.
    Uncommitted data
  25. Occur when a transaction accesses data before and after another transaction finish working with such data.
    Inconsistent retrievals
  26. A special DBMS process that establishes the order in which the operations within concurrent transactions are executed and interleaves the execution of database operations to ensure serializability and isolation of transactions
  27. Schedule of a transaction’s operations in which the interleaved execution of the transactions yields the same results as if the transactions were executed in serial order.
    Serializable schedule
  28. Guarantees exclusive use of a data item to a current transaction.
  29. The use of locks based on the assumption that conflict between transactions is likely to occur.
    Pessimistic locking.
  30. All lock information is managed by a _______, which is responsible for assigning and policing the locks used by the transactions
    lock manager
  31. Indicates the level of lock use.
    Lock granularity
  32. Locking can take place at the following levels:
    • database
    • table
    • page
    • row
    • field (attribute)
  33. The entire database is locked.
    database-level lock
  34. The entire table is locked.
    table-level lock
  35. The DBMS will lock an entire diskpage.
    page-level lock
  36. The equivalent of a diskblock,which can be described as a directly addressable section of a disk.
    diskpage, or page
  37. Allows concurrent transactions to access different rows of the same table even when the rows are located on the same page.
    row-level lock
  38. Allows concurrent transactions to access the same row as long as they require the use of different fields (attributes) within that row.
    field-level lock
  39. Has only two states: locked (1) or unlocked (0).
    binary lock
  40. Exists when access is reservedspecifically for the transaction that locked the object
    exclusive lock
  41. Exists when concurrent transactions are granted read accesson the basis of a common lock
    shared lock
  42. Only one transaction at a time can own an exclusive lock on the same object.
    mutual exclusive rule
  43. Occurs when two transactions wait indefinitely for each other to unlock data
  44. Using the shared/exclusive locking concept, a lock can have three states:
    • unlocked
    • shared (read)
    • exclusive (write)
  45. Defines how transactions acquire and relinquish locks.
    Two-phase locking
  46. The two phases of locking are:
    • growing phase
    • shrinking phase
  47. Transaction acquires all required locks without unlocking any data.
    growing phase
  48. Transaction releases all locks and cannot obtain any new lock.
    shrinking phase
  49. If T1 has not unlocked data item Y, T2 cannot begin; if T2 has not unlocked data item X, T1 cannot continue.Consequently, T1 and T2 each wait for the other to unlock the required data item. Such a deadlock is also known as
    deadly embrace
  50. The three basic techniques to control deadlocks are:
    • Prevention
    • Detection
    • Avoidance
  51. A transaction requesting a new lock is aborted when there is the possibility that a deadlock can occur.
    Deadlock prevention
  52. The DBMS periodically tests the database for deadlocks.
    Deadlock detection
  53. The transaction must obtain all of the locks it needs before it can be executed.
    Deadlock avoidance
  54. The ________ approach to scheduling concurrent transactions assigns a global, unique time stamp to each transaction.
    time stamping
  55. Ensures that no equal time stamp values can exist.
  56. Ensures that time stamp values always increase.
  57. The older transaction rolls back the younger transaction and reschedules it.
  58. The older transaction waits for the younger to complete and release its locks.
  59. Based on the assumption that the majority of the database operations do not conflict and requires neither locking nor time stamping techniques. Instead, a transaction is executed without restrictions until it is committed.
    optimistic approach
  60. Optimistic approach three phases:
    • read
    • validation
    • write
  61. The transaction reads the database, executes the needed computations, and makes the updates to a private copy of the database values.
    read phase
  62. The transaction is validated to ensure that the changes made will not affect theintegrity and consistency of the database
    validation phase
  63. The changes are permanently applied to the database.
    write phase
  64. Restores a database from a given state (usually inconsistent) to a previously consistent state.
    Database recovery
  65. All portions of the transaction must be treated as a single, logical unit of work in which all operations are applied and completed to produce a consistent database
    atomic transaction property
  66. Ensures that transaction logs are always written before any database data are actually updated.
    write-ahead-log protocol
  67. Ensure that a physical disk failure will not impair the DBMS’s ability to recover data.
    Redundant transaction logs
  68. Temporary storage areas in primary memory used to speed up disk operations.
  69. Operations in which the DBMS writes all of its updated buffers to disk.
  70. The transaction operations do not immediately update the physical database. Instead, only the transaction log is updated.
    deferred-write technique
Card Set:
Transaction Management and Concurrency Control
2016-01-13 11:21:13

Chapter 10
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