2. AGENDA
About my company – ANS-ASIA, and me
About SQL Performance
Indexing
Rewrite query
SQLServer tools to improve performance.
3. ABOUT
100% subsidiary of ANS Japan
Address : 10F CMC Tower, Duy Tan Street
Foudation : November 2012
Employees : 30
Business function :Business function :
Software development
Enterprise system (100% Japanese customer up to now)
(Sales management system, Enterprise system for transportation
industry, Tuition management system for university...)
IT consulting
4. ABOUT ME
Name: Trinh Hong Chuong
Skill: 6 years experience in software development
(.Net (VB.Net, C#), T-SQL, PL-SQL, VBA)
Beginner in PHP, PostgreSQL
Interesting in: Reading book, listening music,
walking alone, travelling, ….walking alone, travelling, ….
5. SQL PERFORMANCE
Assess the problem and establish numeric values
that categorize acceptable behavior.
Measure the performance of the system before
modification.
Identify the part of the system that is critical for
improving the performance. This is called
the bottleneck.
improving the performance. This is called
the bottleneck.
Modify that part of the system to remove the
bottleneck.
Measure the performance of the system after
modification.
If the modification makes the performance better,
adopt it. If the modification makes the
performance worse, put it back the way it was.
6. WHAT’S INDEXING
Index is shortcuts to real data
Data type structure: B-Tree
Types of indexes: Clustered, Non-Clustered, XML
index, Fulltext index
7. WHY’S INDEXING
An index is used to speed up searching in the
database.
Indexes can be helpful for a variety of queries
that contain SELECT, UPDATE, DELETE, or
MERGE statements.
Less items in primary keyLess items in primary key
8. CLUSTERED INDEX
Clustered indexes sort and store the data rows in
the table or view based on their key values.
root
Id(from 1 to 4) Id(from 5 to 7)Id(from 1 to 4) Id(from 5 to 7)
Id 1
Name Bill
Dept Dev
Id 2
Name Jobs
Dept HR
Id 7
Name Gate
Dept R&D
9. NON-CLUSTERED INDEX
A nonclustered index contains the nonclustered
index key values and each key value entry has a
pointer to the data row that contains the key
value.
root
Name(from A to F)
Name Bill
Id 1
Name Gate
Id 7
Name Jobs
Id 2
Name(from G to M) Name(from N to Z)
10. IMPROVE INDEX
Create Highly-Selective Indexes
Indexing on columns used in the WHERE clause of
your critical queries frequently improves
performance.
Selectivity is the ratio of qualifying rows to total
rows. If the ratio is low, the index is highly selective.
Create Multiple-Column IndexesCreate Multiple-Column Indexes
11. REWRITE QUERY
Use a search argument (SARG)
SARG operators include =, >, <, >=, <=, IN,
BETWEEN, and sometimes LIKE (in cases of prefix
matching, such as LIKE ‘Bill%')
Non-SARG operators include NOT, <>, NOT EXISTS,
NOT IN, NOT LIKE, and intrinsic functions
12. REWRITE QUERY
Rewrite sub-query into JOIN
Bad sample Good sample
SELECT "Order ID" SELECT DISTINCT O."Order ID"
FROM Orders O
WHERE EXISTS (SELECT "Order ID"
FROM "Order Details"
OD
WHERE O."Order ID" =
OD."Order ID"
AND Discount >= 0.25)
FROM Orders O
INNER JOIN "Order Details" OD
ON
O."Order ID" = OD."Order ID"
WHERE Discount >= 0.25
13. REWRITE QUERY
Don’t use intrinsic functions, type conversion on index column
Bad sample Good sample
DECLARE @limitId = 10
SELECT Name FROM
Employees
DECLARE @limitId = 10
SELECT Name FROM
EmployeesEmployees
WHERE Id - 1 = @limitId
Employees
WHERE Id = @limitId + 1
15. REWRITE QUERY
Index the ORDER-BY / GROUP-BY
CREATE INDEX Emp_Name ON Employees ("Last Name" ASC, "First Name" ASC)
Can help optimize Will not help optimize
... ORDER BY / GROUP BY "Last
Name" ...
... ORDER BY / GROUP BY
"First Name" ...Name" ...
... ORDER BY / GROUP BY "Last
Name", "First Name" ...
"First Name" ...
... ORDER BY / GROUP BY
"First Name", "Last Name" ...
16. REWRITE QUERY
Index the DISTINCT
CREATE INDEX Emp_Name ON Employees ("Last Name" ASC, "First Name" ASC)
Can help optimize Will not help optimize
... DISTINCT "Last Name", "First
Name" ...
... DISTINCT "First Name" ...
... DISTINCT "Last Name" ...Name" ...
... DISTINCT "First Name", "Last
Name" ...
... DISTINCT "Last Name" ...
17. SQLServer tools to improve performance.
Execution plan
CREATE TABLE Employees
(
Id BIGINT NOT NULL,
Name VARCHAR(20) NOT NULL,
Dept VARCHAR(10),
CONSTRAINT [PK_Employee] PRIMARY KEY
CLUSTERED
(Id ASC)
)
CREATE TABLE Employees_Mid
(
Id BIGINT NOT NULL,
Name VARCHAR(20) NOT NULL,
Dept VARCHAR(10),
CONSTRAINT [PK_Employee_Mid] PRIMARY KEY
CLUSTERED
(Id ASC)
)
Query 01
INSERT INTO Employees(Id, Name, Dept)
SELECT Id, Name, Dept FROM Employees_Mid
WHERE Employees_Mid.Id = 1000
Query 02
INSERT INTO Employees(Id, Name, Dept)
SELECT Id, Name, Dept FROM Employees_Mid
WHERE Employees_Mid.Name = ‘A00001’
