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CS403 - Database Management Systems - Lecture Handout 45

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Overview of Lecture:

  • Deadlock Handling
  • Two Phase Locking
  • Levels of Locking
  • Timestamping

This is the last lecture of our course; we had started with transaction management. We were discussing the problems in transaction in which we discussed the locking mechanism. A transaction may be thought of as an interaction with the system, resulting in a change to the system state. While the interaction is in the process of changing system state, any number of events can interrupt the interaction, leaving the state change incomplete and the system state in an inconsistent, undesirable form. Any change to system state within a transaction boundary, therefore, has to ensure that the change leaves the system in a stable and consistent state.

Locking Idea

Traditionally, transaction isolation levels are achieved by taking locks on the data that they access until the transaction completes. There are two primary modes for taking locks: optimistic and pessimistic. These two modes are necessitated by the fact that when a transaction accesses data, its intention to change (or not change) the data may not be readily apparent.

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CS605 - Software Engineering II - Lecture Handout 39

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Environment Assessment

The legacy system also needs to be assessed from an environment’s perspective. This involves looking at the supplier, failure rate, age, performance, support requirements, maintenance cost, and interoperability.

These angles are elaborated in the following paragraph:

Supplier stability: Is the supplier still in existence? Is the supplier financially stable and likely to continue in existence? If the supplier is no longer in business, is the system maintained by someone else?

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