CS4482tut6a - CS4482/6492 Advanced Database Systems...

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CS4482/6492 Advanced Database Systems Tutorial 6 1. One benefit: If there are few tuples in the queried range, then each query can be processed quickly on a single disk. This allows parallel execution of queries with reduced overhead of initiating queries on multiple disks. One drawback: If there are many tuples in the queried range, each query takes a long time to execute as there is no parallelism within its execution. Another drawback: If the queried range is a hot-spot, many queries have to be processed on the same disk and response time will be increased as there is no parallelism to distribute the workload. 2. [21, 31, 51, 76] 3. When there are many small queries, inter-query parallelism gives good throughput. Parallelizing each of these small queries would increase the initiation overhead, without any significant reduction in response time. 4. o In this case, we must first redistribute all the tuples of the two input relations according to a single hash function that involves all the attributes. o
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CS4482tut6a - CS4482/6492 Advanced Database Systems...

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