Prepared by: Anusha Adhikar BBA Sem 3

Prepared by: Anusha Adhikar BBA Sem 3

AMITY GLOBAL BUSINESS SCHOOL

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Goal of database performance is to execute queries as fast as possible

Database performance tuningSet of activities and procedures designed to

reduce response time of database system

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Database performance-tuning activities can be divided into:Client side

Objective is to generate SQL query that returns correct answer in least amount of time, using minimum amount of resources at server end

SQL performance tuning

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Database performance-tuning activities can be divided into (continued):Server side

DBMS environment must be properly configured to respond to clients’ requests in fastest way possible, while making optimum use of existing resources

DBMS performance tuning

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All data in database are stored in data files

Data filesAutomatically expand in predefined

increments known as extendsGenerally grouped in file groups of table

spaces Table space or file group is logical

grouping of several data files that store data with similar characteristics

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DBMS retrieve data from permanent storage and place it in RAM

Data cache or buffer cache is shared, reserved memory area that stores most recently accessed data blocks in RAM

SQL cache or procedure cache is shared, reserved memory area that stores most recently executed SQL statements or PL/SQL procedures, including triggers and functions

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An input/output request is low-level (read or write) data access operation to/from computer devices

Working with data in data cache is many times faster than working with data in data files because DBMS doesn’t have to wait for hard disk to retrieve data

Majority of performance-tuning activities focus on minimizing number of I/O operations

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Listener User Scheduler Lock manager Optimizer

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Refers to number of measurements about database objects and available resourcesTables IndexesNumber of processors usedProcessor speedTemporary space available

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Make critical decisions about improving query processing efficiency

Can be gathered manually by DBA or automatically by DBMS

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DBMS processes queries in three phasesParsingExecutionFetching

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Query optimizer analyzes SQL query and finds most efficient way to access data

Access plans are DBMS-specific and translate client’s SQL query into series of complex I/O operations required to read the data from the physical data files and generate result set

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Rows of resulting query result set are returned to client

DBMS may use temporary table space to store temporary data

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IndexesCrucial in speeding up data accessFacilitate searching, sorting, and using

aggregate functions as well as join operations

Ordered set of values that contains index key and pointers

More efficient to use index to access table than to scan all rows in table sequentially

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Rule-based optimizerUses set of preset rules and points to

determine best approach to execute query Cost-based optimizer

Uses sophisticated algorithms based on statistics about objects being accessed to determine best approach to execute query

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Evaluated from client perspectiveMost current-generation relational DBMSs

perform automatic query optimization at the server end

Most SQL performance optimization techniques are DBMS-specific and are rarely portable

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Indexes are likely used when: Indexed column appears by itself in search

criteria of WHERE or HAVING clause Indexed column appears by itself in GROUP

BY or ORDER BY clauseMAX or MIN function is applied to indexed

columnData sparsity on indexed column is high

Measure of how likely an index will be used

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General guidelines for creating and using indexes:Create indexes for each attribute in WHERE,

HAVING, ORDER BY, or GROUP BY clauseDo not use in small tables or tables with low

sparsityDeclare primary and foreign keys so optimizer

can use indexes in join operationsDeclare indexes in join columns other than

PK/FK

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Normally expressed within WHERE or HAVING clauses of SQL statement

Restricts output of query to only rows matching conditional criteria

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Identify what columns and computations are required

Identify source tables Determine how to join tables Determine what selection criteria is

needed Determine in what order to display

output

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Includes global tasks such as managing DBMS processes in primary memory and structures in physical storage

Includes applying several practices examined in previous section

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DBMS performance tuning at server end focuses on setting parameters used for:Data cacheSQL cacheSort cacheOptimizer mode

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Some general recommendations for creation of databases:Use RAID (Redundant Array of Independent

Disks) to provide balance between performance and fault tolerance

Minimize disk contentionPut high-usage tables in their own table

spaces

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Some general recommendations for creation of databases (continued):Assign separate data files in separate

storage volumes for indexes, system, and high-usage tables

Partition tables based on usageUse denormalized tables where appropriateStore computed and aggregate attributes in

tables

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