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Homework 5

Homework 5. 2PL. Answer Questions 1&2 [True/False+ Explanation]. In a distributed DB, there are three sites, A, B, and C, with communication lines between A & B and B & C (but no direct line between A &C).

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Homework 5

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  1. Homework 5 2PL

  2. Answer Questions 1&2 [True/False+ Explanation] In a distributed DB, there are three sites, A, B, and C, with communication lines between A & B and B & C (but no direct line between A &C). The three sites co-operate in a distributed transaction using the 2PC protocol; A is the coordinator. • If communication is lost between A and B, A could wait indefinitely in a blocked state till communication is restored? • Say that B receives the commit instruction from A but cannot forward such instruction to C since the line between B & C is down. Then B must wait in a blocked state till the line is restored and the instruction to commit can be sent to C. … Questions 3, 4 and 5: next slide.

  3. Questions 3,4 and 5 [True/False+ Explanation] Now say that B receives the commit instruction from A, but immediately after that both the line between A & B and that between B & C fail. Also say that the line between B & C is restored well before the line between A & B. Then: 3. B remains in a blocked state until the line with A is restored, and at that point, it asks A for instructions? 4. C remains in a blocked state till its line with B is restored, and then it ask B for its decision and replicates it? 5. C remains in a blocked state until both lines are restored, and and at that point, it asks A for instructions?

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