1. 4/13/2014 Query Execution Time Calculation and Query Optimization

2. OBJECTIVE The objective of this presentation is to show how to calculate the time required during the execution of a query and then optimize the query. 4/13/2014

3. 1. Query Execution Time 4/13/2014 What is Query? Query is piece of code that is send to a Database in order to get information back from database. It is used to interact with Databse. What is Query ExecutionTime? Query ExecutionTime means time required by query to get the required information from the database.

4. 4/13/2014 HowTo Calculate ??? ? Execution of any query involve CPU time and time to access data from disk. CPU speed are increasing much faster than the disk access time. CPU time as it depends on the low level details of execution code so it is harder to calculate. We have used System time in order to get Execution time. As the System time represent the computer system's notion of the passing of time. System time is measured by a system clock, which is typically implemented as a simple count of the number of ticks Implementation:- The system clock is typically implemented as a programmable interval timer that periodically interrupts the CPU, which then starts executing a timer interrupt service routine.That routine typically adds one tick to the system clock (a simple counter) and handles other periodic housekeeping tasks before returning to whatever the CPU was doing before the interruption.

5. 4/13/2014 Screen Shots:- Advantage:- If we get the execution time then we can reduce that time by using some query optimization method. It also Help in Query Scheduling, Progress Monitoring and also control to System size.

6. 2. Query Optimization 4/13/2014 Introduction Steps in Cost-based query optimization- Query Flow Transformation of Relational Expressions Optimization Algorithms Future Scope Conclusion

7. 4/13/2014 Query Optimization What is Query Optimization??? ? Query optimization is a function of many relational database management systems. The query optimizer attempts to determine the most efficient way to execute a given query by considering the possible query plans. Why ? Many different ways of executing a given query. Huge differences in Execution Time. Increase performance of the system. Uses Less Memory. Lesser Stress on the Database.

8. 4/13/2014 Query Optimization Example: select * from person where ssn = 123 Size of person = 1MB Sequential Scan: Takes 1MB / (20mb/s) = 50ms Use an index on SSN (assuming one exists): Approx 4 Random I/Os = 40ms

9. Query Optimization 4/13/2014 Introduction Steps in Time-based query optimization- Query Flow Transformation of Relational Expressions Optimization Algorithms Future Scope Conclusion

10. 4/13/2014 Steps inTime Based Query Optimization:- 1. Parsing. 2. Transformation. 3. Implementation. 4. Plan selection based onTime estimates. Query Flow:- Processor Code Generator Optimizer Parser SQL Query Language Relational Calculus Relational and Physical Algebra Record at a time calls

11. SQL Structured query Language. It is used to take or any type of data from database or to Interact with database. Query Parser Verify validity of the SQL statement.Translate query into an internal structure using relational calculus. Query Optimizer Find the best expression from various different algebraic expressions. Code Generator/Interpreter -It takes the physical and relational algebra as a input and gave it to the query processor. Query Processor Execute the calls obtained from the code generator. 4/13/2014 Steps inTime Based Query Optimization:-

12. Query Optimization 4/13/2014 Introduction Steps in Time-based query optimization- Query Flow Transformation of Relational Expressions Optimization Algorithms Future Scope Conclusion

13. 4/13/2014 Equivalence of Expressions Two relational expressions equivalent iff: Their result is identical on all legal databases Equivalence rules: Allow replacing one expression with another Examples: 1. 2. Selections are commutative ))(()( 2121 EE ))(())(( 1221 EE

14. 4/13/2014 Pictorial representation of Some more equivalence Rule :-

15. Transformation to Relational Algebra 4/13/2014 Simple Algorithm Start with the original expression Apply all possible applicable rules to get a new set of expressions Repeat with this new set of expressions Till no new expressions are generated

16. 4/13/2014 Find the names of all customers with an account at a Brooklyn branch whose account balance is over $1000. customer_name(branch_city = Brooklyn balance > 1000 (branch (account depositor))) Apply the rules one by one customer_name((branch_city = Brooklyn balance > 1000 (branch account)) depositor) customer_name(((branch_city = Brooklyn (branch)) ( balance > 1000 (account))) depositor) Example

17. Query Optimization 4/13/2014 Introduction Steps in Time-based query optimization- Query Flow Transformation of Relational Expressions Optimization Algorithms Future Scope Conclusion

18. Optimization Algorithms 4/13/2014 Two Types: Exhaustive: That attempt to find the best plan and have dynamic programming. Heuristic: That are simpler, but are not guaranteed to find the optimal plan.

19. 4/13/2014 Heuristic Optimization Dynamic programming is expensive. Use heuristics to reduce the number of choices. Typically rule-based: Perform selection early (reduces the number of tuples) Perform projection early (reduces the number of attributes) Perform most restrictive selection and join operations before other similar operations. Some systems use only heuristics, others combine heuristics with partial time-based optimization.

20. Steps inTypical Heuristic Optimization 4/13/2014 1. Deconstruct conjunctive selections into a sequence of single selection operations . 2. Move selection operations down the query tree for the earliest possible execution . 3. Execute first those selection and join operations that will produce the smallest relations. 4. Replace Cartesian product operations that are followed by a selection condition by join operations. 5. Deconstruct and move as far down the tree as possible lists of projection attributes, creating new projections where needed. 6. Identify those subtrees whose operations can be pipelined, and execute them using pipelining).

21. 4/13/2014 Advantages of Query Optimization 1. Faster Processing of Query. 2. Lesser Cost Per Query. 3. High Performance of The System. 4. Lesser Stress on Database. 5. Lesser Memory is Consumed.

22. Query Optimization 4/13/2014 Introduction. Steps in Time-based query optimization- Query Flow. Transformation of Relational Expressions. Optimization Algorithms.

23. 4/13/2014 Thanks