Assume a quad-core computer system can process database queries at a steady stat

Question

Assume a quad-core computer system can process database queries at a steady state rate of requests per second. Also assume that each transaction takes, on average, a fixed amount of time to process. The following table shows pairs of transaction latency and processing rate. For each of the pairs in the table, answer the following questions:

6.20.1 [10] On average, how many requests are being processed at any given instant?

6.20.2 [10] If move to an 8-core system, ideally, what will happen to the system throughput (i.e., how many queries/second will the computer process)?

6.20.3 [10] Discuss why we rarely obtain this kind of speedup by simply increasing the number of cores.

Explanation / Answer

Answer:

Given in the problem that to assume a quad-core computer system.

So, let the number of cores be

6.20.1)

So, the average number of requests can be given as,

Now, apply the formula for the tabulated data as shown in the question and find the average number of request for each maximum transaction and tabulate them as shown below:

      Average transaction latency

Maximum transaction     processing rate

Average number of requests

1 ms

5000/sec

1.25

2 ms

5000/sec

2.5

1 ms

10,000/sec

2.5

2 ms

10,000/sec

5

6.20.2)

If the computer system is moved from 4-core system to an 8-core system then it will doubles the maximum transaction rate by doubling the number of cores.

6.20.3)

This kind of speedup is rarely obtained by simply increasing the number of cores in the computer system because of the memory contention on the shared memory system.

      Average transaction latency

Maximum transaction     processing rate

Average number of requests

1 ms

5000/sec

1.25

2 ms

5000/sec

2.5

1 ms

10,000/sec

2.5

2 ms

10,000/sec

5

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