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1- Chapter 14 Review Questions 1-11 located at the end of your Database Systems Chapter 11 book. Please use complete sentences and proper grammar. 

1- Chapter 15 Review Questions 1-25 located at the end of your Database Systems Chapter 13 book. Please use complete sentences and proper grammar.

Database Systems: Design,
Implementation, and

Eighth Edition

Chapter 11
Database Performance Tuning and

Query Optimization

Database Systems, 8th Edition 2

  • Objectives
  • • In this chapter, you will learn:
    – Basic database performance-tuning concepts
    – How a DBMS processes SQL queries
    – About the importance of indexes in query processing
    – About the types of decisions the query optimizer has

    to make
    – Some common practices used to write efficient SQL

    – How to formulate queries and tune the DBMS for

    optimal performance
    – Performance tuning in SQL Server 2005

    Database Systems, 8th Edition 3

  • 11.1 Database Performance-Tuning Concepts
  • • Goal of database performance is to execute
    queries as fast as possible

    • Database performance tuning
    – Set of activities and procedures designed to

    reduce response time of database system

    • All factors must operate at optimum level with
    minimal bottlenecks

    • Good database performance starts with
    good database design

    Database Systems, 8th Edition 4

    Database Systems, 8th Edition 5

  • Performance Tuning: Client and Server
  • • Client side
    – Generate SQL query that returns correct answer

    in least amount of time
    • Using minimum amount of resources at server

    – SQL performance tuning

    • Server side
    – DBMS environment configured to respond to

    clients’ requests as fast as possible
    • Optimum use of existing resources

    – DBMS performance tuning

    Database Systems, 8th Edition 6

  • DBMS Architecture
  • • All data in database are stored in data files
    • Data files

    – Automatically expand in predefined increments
    known as extends

    – Grouped in file groups or table spaces
    • Table space or file group:

    – Logical grouping of several data files that store
    data with similar characteristics

    Database Systems, 8th Edition 7

    Basic DBMS architecture

    Database Systems, 8th Edition 8

  • DBMS Architecture (continued)
  • • Data cache or buffer cache: shared, reserved
    memory area
    – Stores most recently accessed data blocks in RAM

    • SQL cache or procedure cache: stores most
    recently executed SQL statements
    – Also PL/SQL procedures, including triggers and


    • DBMS retrieves data from permanent storage and
    places it in RAM

    Database Systems, 8th Edition 9

    DBMS Architecture (continued)

    • Input/output request: low-level data access
    operation to/from computer devices, such as
    memory, hard disks, videos, and printers

    • Data cache is faster than data in data files
    – DBMS does not wait for hard disk to retrieve data

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

    • Typical DBMS processes:
    – Listener, User, Scheduler, Lock manager, Optimizer

    Database Systems, 8th Edition 10

  • Database Statistics
  • • Measurements about database objects and available
    – Tables, Indexes, Number of processors used,

    Processor speed, Temporary space available
    • Make critical decisions about improving query

    processing efficiency
    • Can be gathered manually by DBA or automatically by

    – UPDATE STATISTICS table_name [index_name]
    – Auto-Update and Auto-Create Statistics option

    • 資料庫屬性 -> 自動更新統計資料
    • 資料庫屬性 -> 自動建立統計資料

    Database Systems, 8th Edition 11

    Database Systems, 8th Edition 12

    Ch08: dbcc show_statistics (customer, PK__CUSTOMER__24927208 )

    Ch08: dbcc show_statistics (customer, CUS_UI1)

    補充 SQL Server 2005

    Database Systems, 8th Edition 13

  • 11.2 Query Processing
  • • DBMS processes queries in three phases
    – Parsing

    • DBMS parses the query and chooses the most
    efficient access/

    execution plan

    – Execution
    • DBMS executes the query using chosen

    execution plan

    – Fetching
    • DBMS fetches the data and sends the result back

    to the client

    Database Systems, 8th Edition 14
    Query Processing

    Database Systems, 8th Edition 15

  • SQL Parsing Phase
  • • Break down query into smaller units
    • Transform original SQL query into slightly

    different version of original SQL code
    – Fully equivalent

    • Optimized query results are always the same as
    original query

    – More efficient
    • Optimized query will almost always execute faster

    than original query

    Database Systems, 8th Edition 16

  • SQL Parsing Phase (continued)
  • • Query optimizer analyzes SQL query and finds most

    efficient way to access data
    – Validated for syntax compliance

    – Validated against data dictionary
    • Tables, column names are correct
    • User has proper access rights

    – Analyzed and decomposed into more atomic components

    – Optimized through transforming into a fully equivalent but
    more efficient SQL query

    – Prepared for execution by determining the execution or
    access plan

    Database Systems, 8th Edition 17

    SQL Parsing Phase (continued)

    • Access plans are DBMS-specific
    – 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
    • DBMS checks if access plan already exists for

    query in SQL cache
    • DBMS reuses the access plan to save time
    • If not, optimizer evaluates various plans

    – Chosen plan placed in SQL cache

    Database Systems, 8th Edition 18

    Database Systems, 8th Edition 19

  • SQL Execution and Fetching Phase
  • • All I/O operations indicated in access plan are
    – Locks acquired
    – Data retrieved and placed in data cache
    – Transaction management commands processed

    • Rows of resulting query result set are returned to

    • DBMS may use temporary table space to store
    temporary data
    – The server may send only the first 100 rows of 9000 rows

    Database Systems, 8th Edition 20

  • Query Processing Bottlenecks
  • • Delay introduced in the processing of an I/O
    operation that slows the system
    – CPU

    – RAM

    – Hard disk

    – Network

    – Application code

    Database Systems, 8th Edition 21

    SQL 敘述
    詢 , 請按


    Database Systems, 8th Edition 22

  • 11.3
  • Indexes and Query Optimization
  • • Indexes
    – Crucial in speeding up data access

    – Facilitate 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

    Database Systems, 8th Edition 23

    Indexes and Query Optimization
    • Data sparsity: number of different values a column

    could possibly have
    • Indexes implemented using: ( 課本 p. 453)

    – Hash indexes

    – B-tree indexes: most common index type. Used in tables in
    which column values repeat a small number of times. The
    leaves contain pointers to records It is self-balanced.

    Bitmap indexes

    : 0/1

    • DBMSs determine best type of index to use
    – Ex: CUST_LNAME with B-tree and REGION_CODE with

    Bitmap indexes

    Database Systems, 8th Edition 24B-tree and bitmap index representation


    Index Representation for the
    CUSTOMER table

    Requires only 5 accesses to STATE_INDEX,
    5 accesses to CUSTOMER

    Database Systems, 8th Edition 26

  • 11.4 Optimizer Choices
  • • Rule-based optimizer
    – Preset rules and points

    – Rules assign a fixed cost to each operation

    • Cost-based optimizer
    – Algorithms based on statistics about objects

    being accessed

    – Adds up processing cost, I/O costs, resource
    costs to derive total cost

  • Example
  • Database Systems, 8th Edition 27


    • With the following database statistics:
    – The PRODUCT table has 7000 rows
    – The VENDOR table has 300 rows
    – 10 vendors come from Florida
    – 1000 products come from vendors in Florida

    Database Systems, 8th Edition 28


    Database Systems, 8th Edition 29

    • Assume the PRODUCT table has the index
    PQOH_NDX in the P_QOH attribute


    could be resolved by reading only the first entry in
    the PQOH_NDX index

    Database Systems, 8th Edition 30

  • Using Hints to Affect Optimizer Choices
  • • Optimizer might not choose best plan
    • Makes decisions based on existing statistics

    – Statistics may be old
    – Might choose less efficient decisions

    • Optimizer hints: special instructions for the
    optimizer embedded in the SQL command text

    Database Systems, 8th Edition 31

    Oracle 版本

    Database Systems, 8th Edition 32

    MS SQL Server 的語法請參考:


    SQL Server Query Hints Example

    select o.customerid,companyname
    from orders as o inner MERGE join customers as c
    on o.customerid = c.customerid

    select o.customerid,companyname
    from orders as o inner HASH join customers as c
    on o.customerid = c.customerid

    select o.customerid,companyname
    from orders as o inner LOOP join customers as c
    on o.customerid = c.customerid

    select city, count(*)
    from customers
    group by city

    • Database Systems: Design, Implementation, and Management Eighth Edition
    • Objectives
      11.1 Database Performance-Tuning Concepts

    • PowerPoint Presentation
    • Performance Tuning: Client and Server
      DBMS Architecture

    • Slide 7
    • DBMS Architecture (continued)

    • Slide 9
    • Database Statistics

    • Slide 11
    • Slide 12
    • 11.2 Query Processing

    • Slide 14
    • SQL Parsing Phase
      SQL Parsing Phase (continued)

    • Slide 17
    • Slide 18
    • SQL Execution and Fetching Phase
      Query Processing Bottlenecks

    • Slide 21
    • 11.3 Indexes and Query Optimization
      Indexes and Query Optimization

    • Slide 24
    • Slide 25
    • 11.4 Optimizer Choices

    • Slide 28
    • Slide 29
    • Using Hints to Affect Optimizer Choices

    • Slide 31
    • Slide 32

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