Analyze and tune SQL Query

Why need tune Sql query

Increase performance Save time and money

Measurement Methods

Benchmarking MySQL Enterprise Monitor (MEM), Query Analyzer Performance schema, MySQL sys schema EXPLAIN Optimizer trace Slow log Status variables (SHOW STATUS LIKE ’Handler%’) Profile

Index

Some type of Index:B-Tree indexHash indexR-Tree index

The use of indexes to find rows faster Writes become slower with each added index

Query Processing

EXPLAIN

With EXPLAIN the query is sent all the way to the optimizer, but not to the storage engine

Instead EXPLAIN returns the query execution plan EXPLAIN tells you:

– In which order the tables are read – What types of read operations that are made – Which indexes could have been used – Which indexes are used – How the tables refer to each other – How many rows the optimizer estimates to retrieve from each table

Database Designing (Optimizing Schemas)

Normalization

Normalization is a key factor in optimizing your database structure Good normalization prevents redundant data from being stored in the

same tables By moving redundant data to their own table, this reduces storage

requirements and overhead when processing queries data warehousing and reporting system a star-schema might be a

better solution

Table Optimizations

Use columns that are as short as possible; – INT instead of BIGINT – VARCHAR(10) instead of VARCHAR(255)

Pay special attention to columns that are used in joins Define columns as NOT NULL if possible

Index Optimizations

An index on the whole column is not necessary – Instead index just a prefix of a column – Prefix indexes take less space and the operations are faster

Composite indexes can be used for searches on the first column(s) in the index

Minimize the size of PRIMARY KEYs that are used as references in other tables

Using an auto_increment column can be more optimal A FULLTEXT index is useful for:word searches in text, searches on

several columns

Click to add textClick to add text

Optimizing Where Condition

Selecting Access Method

find the best access method: – Check if the access method is useful – Estimate cost of using access method – Select the cheapest to be used

Choice of access method is cost based Finding the optimal method to read data from storage engine

Main access methods: - Table scan - Index scan - Ref access - Range scan - Index merge - Loose index scan

Ref Access

id select type

table type possible key key length

ref

1 SIMPLE order ref i_o_orderdate i_o_custkey

i_o_orderdate

4

2 SIMPLE customer eq_ref PRIMARY PRIMARY order.c_custkey

EXPLAIN SELECT * FROM orders JOIN customer ON c_custkey = o_custkey WHERE o_orderdate = ‘1992-09-12’

Change Where Condition To Use Index SELECT *

FROM customerWHERE SUBSTRING(c_name,1,1) = 'C'

SELECT *FROM customerWHERE c_name >= 'C' and c_name < ‘D’

SELECT *FROM customerWHERE c_name like 'C%'

Change Where Condition To Use Index Change where condition into

F(field) > const ->filed > G(const)

Force Index - Ignore Index

Select id From data where type = 100 and level > 3order by id;

Select id From data use index(type)where type = 100 and level > 3 order by id;

Select id From data ignore index(type) where type = 100 and level > 3 order by id;

Join Optimizer

Join Optimizer

STRAIGHT_JOIN

STRAIGHT_JOIN is similar to JOIN, except that the left table is always read before the right table. This can be used for those (few) cases for which the join optimizer puts the tables in the wrong order.

Using Filesort

“Filesort”: – Store query result in temporary table before sorting – If data volume is large

Optimizations: – index to generate query result in sorted order – For ”LIMIT n” queries.

Compare Join Vs In

SELECT requestID, request_titleFROM Request rWHERE EXISTS( SELECT * FROM User WHERE userID=r.userID)

SELECT requestID, request_titleFROM Request rJOIN FROM User USING(serID)

Join With Federate Table

CREATE TABLE federated_table (

id INT(20) NOT NULL AUTO_INCREMENT,

name VARCHAR(32) NOT NULL DEFAULT '',

other INT(20) NOT NULL DEFAULT '0',

PRIMARY KEY (id),

INDEX name (name),

INDEX other_key (other)

)

ENGINE=FEDERATED

DEFAULT CHARSET=latin1 CONNECTION='mysql://fed_user@remote_host:9306/federated/test_table';

Question and Answer

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