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Concurrent Access Problems

Concurrent Access Problems. On Transaction Processing. Concurrent Access Problems. 3 Problems: Lost Updates Uncommitted Data Inconsistent Retrieval. Lost Updates. Assume Transaction 1 : Update Inventory set PROD_QOH=PROD_QOH+100; Transaction 2 : Update Inventory

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Concurrent Access Problems

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  1. Concurrent Access Problems On Transaction Processing

  2. Concurrent Access Problems • 3 Problems: • Lost Updates • Uncommitted Data • Inconsistent Retrieval

  3. Lost Updates Assume Transaction 1: Update Inventory set PROD_QOH=PROD_QOH+100; Transaction 2: Update Inventory set PROD_QOH=PROD_QOH-30;

  4. Lost Updates • Transaction 1: 3 processes • Read PROD_QOH • PROD_QOH=PROD_QOH+100 • WRITE PROD_QOH

  5. Lost Updates Table 9.2 Table 9.3

  6. Uncommitted Data Assume Transaction 1: Update Inventory set PROD_QOH=PROD_QOH+100; Rollback; Transaction 2: Update Inventory set PROD_QOH=PROD_QOH-30;

  7. Uncommitted Data Table 9.4 Table 9.5

  8. Inconsistent Retrievals Table 9.6 Table 9.7

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