Database chapter 10 questions
- 1. Justin Andrews ACSG 552 Chapter 10 Questions 2. The three most common concurrent transaction execution problems are lost updates, uncommitted data, and inconsistent retrievals. Concurrency control can help avoid these problems through its ability to coordinate simultaneous executions of transactions in a multiprocessing database system. This is accomplished with various methods, including the use of a scheduler and locks. 3. The DBMS component responsible for concurrency control is a scheduler, which is a process that establishes the order in which the many operations during each transaction are executed. 5. Database recovery takes place through the use of data in a given transaction log to recover a database from an inconsistent to a consistent state. A write-ahead-log protocol ensures that transaction logs are always written before any database data are actually updated, ensuring that the database can later be recovered to a consistent state. Redundant transaction logs ensure a physical disk failure will not impair the DBMS’s ability to recover data. Database buffers are used to store copies of data from physical disks, which are themselves updated when a transaction updates data, to help speed up operations. The updated copies of data in the buffers are eventually used to update the data on the physical disks. Checkpoints are the process in which a DBMS writes updated buffers onto a disk, with no other requests being executed during it. Deferred-write techniques delay the update of a physical database, only allowing the transaction log to update. The database itself will only update after a given transaction reaches a commit point, which uses information from the transaction log. If the transaction aborts, no changes will be made, preventing a need to undo the changes. Write-through techniques differ from deferred-write techniques as they proceed to have the database updated immediately. When a transaction aborts in this instance, the changes need to be undone through a ROLLBACK operation. 6. a. BEGIN TRANSACTION UPDATE CUSTOMER SET CUS_BALANCE = CUS_BALANCE + ((110 * 0.08) + 110) WHERE CUS_CODE = ‘10010’ UPDATE CUSTOMER SET CUS_DATELSTPUR = ‘05/11/10’ WHERE CUS_CODE = ‘10010’ UPDATE INVOICE
- 2. SET INV_NUMBER = ‘10983’ WHERE CUS_CODE = ‘10010’ UPDATE INVOICE SET INV_TERMS = ‘30’ WHERE CUS_CODE = ‘10010’ UPDATE INVOICE SET INV_DATE = ‘05/11/10’ WHERE CUS_CODE = ‘10010’ UPDATE INVOICE SET INV_TOTAL = (110 * 0.08) + 110 WHERE CUS_CODE = ‘10010’ UPDATE INVOICE SET INV_STATUS = ‘OPEN’ WHERE CUS_CODE = ‘10010’ COMMIT; 6. b. BEGIN TRANSACTION UPDATE CUSTOMER SET CUS_BALANCE = CUS_BALANCE – 100 WHERE CUS_CODE = ‘10983’ UPDATE CUSTOMER SET CUS_DATELSTPMT = ‘06/03/10’ WHERE CUS_CODE = ‘10983’ UPDATE PAYMENT SET PMT_ID = ‘3428’ WHERE CUS_CODE = ‘10983’ UPDATE PAYMENT SET PMT_DATE = ‘06/03/10’ WHERE CUS_CODE = ‘10983’ UPDATE PAYMENT SET PMT_AMT = 100 WHERE CUS_CODE = ‘10983’ UPDATE PAYMENT SET PMT_TYPE = ‘CASH’ WHERE CUS_CODE = ‘10983’
- 3. COMMIT; 7. TRANSACTION TRANSACTION WAIT/DIE WOUND/WAIT REQUESTING OWNING LOCK SCHEME SCHEME LOCK T1 (11194185) T2 (13582019) T1 waits until T2 is T1 rolls back T2. completed and T2 is rescheduled releases its locks. while using the same time stamp. T2 (13582019) T1 (11194185) T2 rolls back. T2 waits until T1 is T2 is rescheduled completed and using the same time releases its locks. stamp. 8. 1. Table-level lock – Necessary as both the CUSTOMER and INVOICE tables are accessed. 2. Data manipulation – Regarding two instances of editing in the CUSTOMER table. 3. Data manipulation – Regarding five instances of editing in the INVOICE table. 4. Table-level unlock – For when the data manipulation is finished. 9. 1. Row-level lock – Necessary for modifying information of a single customer in the CUSTOMER table. 2. Row-level lock – Necessary for modifying information of a single invoice in the INVOICE table. 3. Data manipulation – Regarding two instances of editing in the CUSTOMER table. 4. Data manipulation – Regarding five instances of editing in the INVOICE table. 5. Row-level unlock – For when one is finished modifying the information in the CUSTOMER table. 6. Row-level unlock – For when one is finished modifying the information in the INVOICE table. 10. 1. Table-level lock – Necessary as both the CUSTOMER and PAYMENT tables are accessed. 2. Data manipulation – Regarding two instances of editing in the CUSTOMER table. 3. Data manipulation – Regarding four instances of editing in the PAYMENT table. 4. Table-level unlock – For when the data manipulation is finished. 11. 1. Row-level lock – Necessary for modifying information of a single customer in the CUSTOMER table.
- 4. 2. Row-level lock – Necessary for modifying information of a single invoice in the PAYMENT table. 3. Data manipulation – Regarding two instances of editing in the CUSTOMER table. 4. Data manipulation – Regarding four instances of editing in the PAYMENT table. 5. Row-level unlock – For when one is finished modifying the information in the CUSTOMER table. 6. Row-level unlock – For when one is finished modifying the information in the PAYMENT table.