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Unformatted text preview: Advanced Database Systems - CSCI-GA.2434-001 - Fall 2011 Professor: Dennis Shasha Homework 1 - Due: Tuesday, October 11, 2011 Please send to [email protected] Each question is worth 10 points. You may work with one partner and sign both of your names to your paper. 1. For each of the following example executions, determine if it is serializable, assuming each active transaction ultimately commits. (a) Read 1 ( x ); Write 2 ( x ); Write 2 ( y ); Read 3 ( y ); Read 3 ( z ) (b) Read 1 ( x ); Write 2 ( x ); Write 2 ( y ); Read 3 ( y ); Read 3 ( z ); Write 1 ( z ) (c) Read 1 ( x ); Write 2 ( x ); Write 2 ( y ); Read 3 ( y ); Write 1 ( z ); Read 3 ( z ) (d) Read 1 ( x ); Write 2 ( y ); Read 1 ( y ); Write 2 ( z ); Read 3 ( z ); Write 3 ( z ); Read 1 ( z ) 2. Try to complete the proof of the serialization graph theorem by showing the final write portion. 3. Consider the two phase locking protocol with reads and writes. (a) Is two phase locking deadlock-free? If so, prove it. If not, illustrate a deadlock situation. That is, you must illustrate a situation in which there is a cycle in the waits-for graph. (b) I stated in class that most deadlocks will involve few transactions. Assuming the prob- ability of conflict is small and conflicts on different variables are mutually independent (a simplifying assumption, but not bad in practice), show why this might be so. You may assume that all transactions access the same number of data items and all data items are accessed with equal probability. Equivalently, please assume that any accessitems are accessed with equal probability....
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- Spring '11
- data items, Locks, release lock, phase locking