COSI 127b Lecture Notes - Lecture 8: Network Delay, Query Plan, Query Optimization
27 Apr 2020
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Document Summary
In a b+ tree, there must be the same distance from the root to any leaf. Also, the nodes must be at least half full. A cost model is a collection of formulas used to predict the cost of a query optimization plan. Query plan execution time is influenced by disk i/o time, cpu time, and the network latency. Usually, the main cost that influences the query plan execution time is disk i/o time. Typically, the cpu time is the least concerning factor for query plan execution time. Network latency is often an issue for distributed systems. I/o cost is dependent on the storage order of the relations, the sizes of the indexes and their availability, and the size of the relations in terms of blocks and tuples. Sorted merge joins are only applicable for joins on an equality conditional. Bnlj joins are ideal when a relation fits in memory.
