Question: Show that the lowest cost join order can be computed in
Show that the lowest-cost join order can be computed in time O(3n). Assume that you can store and look up information about a set of relations (such as the optimal join order for the set, and the cost of that join order) in constant time. (If you find this exercise difficult, at least show the looser time bound of O(22n).)
Answer to relevant QuestionsShow that, if only left-deep join trees are considered, as in the System R optimizer, the time taken to find themost efficient join order is around n2n.Assume that there is only one interesting sort order.List the ACID properties. Explain the usefulness of each. Consider the following two transactions: T1: read (A); read (B); if A = 0then B: = B + 1; write (B). T2: read (B); read (A); if B = 0 then A: = A + 1; write (A). Let the consistency requirement be A = 0 ∨ B = 0, ...Most implementations of database systems use strict two-phase locking. Suggest three reasons for the popularity of this protocol.When a transaction is rolled back under timestamp ordering, it is assigned a new timestamp. Why can it not simply keep its old timestamp?
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