For each of the following statements, decide whether it is true or false. Please

Question

For each of the following statements, decide whether it is true or false. Please use a sentence or two to explain why. Answer and explanation needed.

--Given the parameters for the following disks, disk 2 is the best.

Disk 1: seek time 5 milliseconds, 5400 rpm

Disk 2: seek time 4 milliseconds, 10000 rpm

Disk 3: seek time 4 milliseconds, 7200 rpm

---To check whether an index is used to answer a SQL query, you can simply run the same query twice, the first time before the creation of the index and the second time after creation of the index and check whether the second execution is faster than the first one.

---Query optimization is done manually by DBA because DBA knows how to execute a SQL statement efficiently.

Explanation / Answer

1. True. Because total access time is less in the second Disk.

Disk 1: 5400 RPM= 60 Revolution/Sec = 11 ms/ revolution

Disk 2: 10000 RPM = 166.67 Revolution/sec = 6ms/revolution

Disk 3: 7200 RPM = 120 revoloution/sec = 8.33ms/revolution

2. True, Index is used to answer the queries. Because index will increase the performance in terms of response time/access time. #Index is creating by already visiting and scanned pages.

3. False, Nowdays Query optimization are already coming inbuilt in various RDBMS. Because today is very difficult to done manually by DBA due to bigger database and complex SQL queries.

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