Chapter 25: Problem 11

Discuss the different techniques for executing an equijoin of two files located at different sites. What main factors affect the cost of data transfer?

Short Answer

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Equijoin execution techniques include Nested-Loop Join, Sort-Merge Join, and Hash Join. Factors affecting data transfer cost include bandwidth, latency, data size, and network congestion.

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Definition of Equijoin

An equijoin is a type of join that combines tables based on an equality between the values in the columns of these tables.

Different Techniques for Executing an Equijoin

Three common methods used for executing an equijoin include: \n1. Nested-Loop Join: This technique uses a nested loop where for each tuple in the first table, the system scans the entire second table. This method is simple but can be very inefficient if the tables are large.\n2. Sort-Merge Join: Here, the tuples from both tables are sorted on the join attributes, and the sorted lists are merged. This method can be efficient if the tables are already sorted or nearly sorted.\n3. Hash Join: In a hash join, a hash table is built using the smaller table, and then the larger table is scanned and matched with the hash table. This can be very efficient if the hash table fits in memory.

Factors Affecting the Cost of Data Transfer

1. Bandwidth: The greater the bandwidth of the network, the more data can be transferred in a given time, reducing the cost.\n2. Latency: The delay to begin transferring data across the network can add to the cost.\n3. Data Size: Larger data sizes may require more resources to transmit, increasing the cost.\n4. Network Congestion: The more congested the network is, the slower the data transfer, increasing the cost of the transfer.

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Discuss the different techniques for executing an equijoin of two files located at different sites. What main factors affect the cost of data transfer?

Short Answer

Step by step solution

Definition of Equijoin

Different Techniques for Executing an Equijoin

Factors Affecting the Cost of Data Transfer

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