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Concurrent Access Problems

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Concurrent Access Problems On Transaction Processing Concurrent Access Problems 3 Problems: Lost Updates Uncommitted Data Inconsistent Retrieval Lost Updates Assume ... – PowerPoint PPT presentation

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Title: Concurrent Access Problems


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_QOHPROD_QOH100
  • Transaction 2
  • Update Inventory
  • set PROD_QOHPROD_QOH-30

4
Lost Updates
  • Transaction 1 3 processes
  • Read PROD_QOH
  • PROD_QOHPROD_QOH100
  • WRITE PROD_QOH

5
Lost Updates
Table 9.2
Table 9.3
6
Uncommitted Data
  • Assume
  • Transaction 1
  • Update Inventory
  • set PROD_QOHPROD_QOH100
  • Rollback
  • Transaction 2
  • Update Inventory
  • set PROD_QOHPROD_QOH-30

7
Uncommitted Data
Table 9.4
Table 9.5
8
Inconsistent Retrievals
Table 9.6
Table 9.7
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