This question is in regards to distributed databases: Many thanks in advance and

Question

This question is in regards to distributed databases:

Many thanks in advance and have a good day.

We study a distributed database of 3 sites that stores a single table T. Our workload is that site 1 issues 30 queries to T per hour, site 2 issues 25, and site 3 issues 10. Similarly, site 1 issues 2 updates to T per hour, site 2 28, and site 3 90. Executing a query locally at a site costs 1, executing remotely if there is no local copy costs 10. Similarly, the cost of locally updating is 5, and 50 for each remote site. Which sites should replicate T? Describe how you arrived at this conclusion. Now, generalize this problem as follows: we study a distributed database of n sites that stores a single table T. Our workload is that each of the sites i issues qi queries and ui updates to T per hour Executing a query locally at a site costs c, executing remotely if there is no local copy costs 10c. Similarly, the cost of locally updating is d, and 10d for each remote site. Describe how to choose the sites at which to replicate T with respect to c and d. a. b.

Explanation / Answer

Solution:

Let's calculate the costs of each site first for every operation

site 1:

Locally: 30 * 1 + 2 * 5 = 40

Globally: 30 * 10 + 2 * 50 = 400

Time save(if stored locally)= 360

sire 2:

Locally: 25 * 1 + 28 * 5 = 165

Globally: 25 * 10 + 28 * 50 = 1650

TIme saved (if stored locally)= 1650-165 = 1485

site 3:

Locally: 10 * 1 + 90 * 5 = 460

Globally: 10 * 10 + 90 * 50 = 4600

TIme saved (if stored locally)= 1650-165 = 4140

a)

SIte 3 since it will save most of the time.

b)

As shown above, in the calculations whichever site is saving the most time should be calculated first and then the decision should be taken to replicate the site.

I hope this helps if you find any problem. Please comment below. Don't forget to give a thumbs up if you liked it. :)

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