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Concurrent Access Problems

This article discusses three major concurrent access problems in transaction processing: Lost Updates, Uncommitted Data, and Inconsistent Retrieval. It explains how lost updates occur when multiple transactions attempt to update the same data simultaneously, leading to the loss of one transaction's result. Uncommitted data refers to the scenario where one transaction reads data modified by another uncommitted transaction. Inconsistent retrieval occurs when a transaction retrieves data that is being modified by other transactions. Examples and tables are provided for better understanding.

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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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