Query Processing and Query Optimisation
代做project | assignment | 代写sql – 本题是一个database基础理论进行练习的代做, 对sql的编写优化进行训练解析, 涵盖了database原理等方面, 这个项目是assignment代写的代写题目
assignment 3 Query Processing and Query Optimisation
Question 1 (5 marks)
Consider two relations called Parts and Supply. Imagine that relation Parts has 60 ,000 tuples and Supply has 150 , 0 00 tuples. Both relations store 50 tuples per page. Consider the following sql statement:
SELECT *
FROM Parts INNER JOIN Supply
ON Parts.PartID = Supply.PID;
We wish to evaluate an equijoin between Supply and Parts, with an equality condition Parts.PartID = Supply.PID. There are 20 2 buffer pages available in memory for this operation. Both relations are stored as (unsorted) heap files. Neither relation has any indexes built on it.
Consider the alternative join strategies described below and calculate the cost of each alternative. Evaluate the algorithms using the number of disk I/O’s (i.e. pages) as the cost. For each strategy, provide the formulae you use to calculate your cost estimates.
a) Page-oriented Nested Loops Join. Consider Parts as the outer relation. (1 mark)
b) Block-oriented Nested Loops Join. Consider Parts as the outer relation. (1 mark)
c) Sort-Merge Join. Assume that Sort-Merge Join can be done in 2 passes. (1 mark)
d) Hash Join. (1 mark)
e) What would be the lowest possible cost to perform this query, assuming that no
indexes are built on any of the two relations, and assuming that sufficient buffer space
is available? What would be the minimum buffer size required to achieve this cost?
Explain briefly. (1 mark)
Question 2 (5 marks)
Consider a relation with the following schema:
Employee (EmpID, firstname, lastname, department, salary)
The Employee relation has 1200 pages and each page stores 12 0 tuples. The department attribute can take one of six values (Marketing, Human Resource, Finance, Public Relations, Sales and Distribution, Operation Management) and salary can have values between 10 0,000 and 500,000 ([ 10 0,000, 500,000]).
Suppose that the following SQL query is executed frequently using the given relation:
SELECT *
FROM Employee
WHERE salary > 300 ,000 AND department = Marketing;
Your job is to analyse the query plans and estimate the cost of the best plan utilizing the information given about different indexes in each part.
a) Compute the estimated result size for the query, and the reduction factor of each filter.
(1 mark)
b) Compute the estimated cost of the best plan assuming that a clustered B+ tree index
on (department, salary) is the only index available. Suppose there are 300 index
pages. Discuss and calculate alternative plans. (1 mark)
c) Compute the estimated cost of the best plan assuming that an unclustered B+ tree
index on (salary) is the only index available. Suppose there are 200 index pages.
Discuss and calculate alternative plans. (1 mark)
d) Compute the estimated cost of the best plan assuming that an unclustered Hash index
on (department) is the only index available. Discuss and calculate alternative plans.
(1 mark)
e) Compute the estimated cost of the best plan assuming that an unclustered Hash index
on (salary) is the only index available. Discuss and calculate alternative plans.
(1 mark)
Question 3 (10 marks)
Consider the following relational schema and SQL query. The schema captures information about employees, their departments and the projects they are involved in.
Employee (eid: integer, salary: integer, name: char(30))
project (projid: integer, code: char(20), start: date, end: date, eid: integer)
Department (did: integer, projid: integer, budget: real, floor: integer)
Consider the following query:
SELECT e.name, d.projid
FROM Employee e, Project p, Department d
WHERE e.eid = p.eid AND p.projid = d.projid
AND e.salary < 300,000 AND p.code = alpha 340;
The systems statistics indicate that there are 1000 different project code values, and salary of the employees range from 100,000 to 500,000 ([100,000, 500,000]). There is a total of 60,000 projects, 5,000 employees and 20,000 departments in the database. Each relation fits 100 tuples in a page. Assume eid is a candidate key for Employee, projid is a candidate key for Project, and did is a candidate key for the Department table. Suppose there exists a clustered B+ tree index on (Project.projid) of size 200 pages and suppose there is a clustered B+ tree index on (employee.salary) of size 10 pages.
a) Compute the estimated result size and the reduction factors (selectivity) of this query.
(2 marks)
b) Compute the cost of the plans shown below. Assume that sorting of any relation (if
required) can be done in 2 passes. NLJ is a Page-oriented Nested Loops Join.
Assume that 100 tuples of a resulting join between Employee and Project fit in a page.
Similarly, 100 tuples of a resulting join between Project and Department fit in a page.
If selection over filtering predicates is not marked in the plan, assume it will happen
on-the-fly after all joins are performed, as the last operation in the plan.
(8 marks, 2 marks per plan)
Formatting Requirements:
For each question, present an answer in the following format:
- Show the question number before each question. You do not need to include the text of the question itself.
- Show your answer in blue text (please type your answers on a computer).
- Start Question 2 and Question 3 on a new page.
For each of the calculations, provide all the formulae you used to calculate your cost estimates, and show your working, not only the result.
Employee
(Heap scan)
Project
(Heap scan)
Department
(Heap scan)
Project
(Heap scan)
Department
(Heap scan)
Employee
(Heap scan)
NLJ
NLJ
HJ
SMJ
[1] [2]
[3] [4]
Project
Employee (Heap scan)^
(Index scan (salary))
Department
(Heap scan)
NLJ
HJ
(salary <300,000)
Department
(Heap scan)
Project
(Index scan (projid))
Employee
(Heap scan)
SMJ
SMJ
Submission Process:
Submit a single PDF showing your answers to all questions to the Assessment page on LMS by 6pm on the due date of Friday 18 October. Name your file STUDENT_ID.pdf, where STUDENT_ID corresponds to YOUR student id.
Requesting a Submission Deadline Extension
If you need an extension due to a valid (medical) reason, you will need to provide evidence to support your request by 9pm, Thursday 1 7 th of October. Medical certificates need to be at least two days in length. To request an extension:
- Email Farah Khan ([email protected]) from your university email address, supplying your student ID, the extension request and supporting evidence.
- If your submission deadline extension is granted you will receive an email reply granting the new submission date. Do not lose this email! Replies may take up to 12 hours, so please be patient.
Reminder: INFO20003 Hurdle Requirements
To pass INFO20003 you must pass two hurdles:
- Hurdle 1: Obtain at least 50% (15/30) or higher for the three assignments (each worth 10%)
- Hurdle 2: Obtain a grade of 50% (35/70) or higher for the End of Semester Exam
Therefore, it is our recommendation to students that you attempt every assignment and every question in the exam.