Mysql index

MySQL IndexAndy Yao

Friday, December 30, 11

MySQL Basic


MySQL Architecture


Storage Engine: MyISAM

Table lock

No automated data recovery

No transactions

Only indexes are cached in memory

Compact storage


Storage Engine: InnoDB

Transactional

Foreign keys

Multiversioning

Clustered by primary key

No cached count(*)

Blocking AUTO_INCREMENT

Optimized cache


InnoDB Storage Architecture Tablespaces

leaf node segment

non-leaf node segment

rollback node segment

Segment

extent

extent

extent

extent

...

Extent

row row

row row

...

PageRow

trx id

row id

roll pointer

col 1 col n... 64 pages


InnoDB and File system

File system -‐> InnoDB -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ disk partition -‐> tablespace file -‐> segment inode -‐> fsp0fsp.c 'inode' fs space allocation unit -‐> extent disk block -‐> page (16 kB)


Types of Indexes


Types of Indexes

B+Tree indexes

Hash indexes

R-Tree indexes

Full-text indexes


B+Tree Indexes


Binary search tree

2

3

5

7

6 8

2

3

6

7

85

Binary search tree AVL tree


B Tree

25 50 75 ...

5 10 15 20 25 30 50 55 60 65 75 80 85 90


B+Tree

25 50 75 ...

5 10 15 20 25 30 50 55 60 65 75 80 85 90


B+Tree Indexes


B+tree indexes: Demo

CREATE TABLE People (last_name varchar(50) not null,first_name varchar(50) not null,dob date not null,gender enum('m', 'f') not null,

key(last_name, first_name, dob) );


B+tree indexes: Demo


B+Tree: Types of queries

Match the full value

where last_name=? and first_name=? and bod=?

Match a leftmost prefix

where last_name=?

where last_name=?



Match a column prefix

where last_name like ”Liang%”

Match a range of values

where last_name > ?



Match one part exactly and match a range on another

where last_name=? and first_name>?

Index only queries

select first_name where last_name=?


B+Tree: Limitations

Doesn’t start from leftmost

where first_name=?

Skip columns in the index

where last_name=? and bod=?


B+Tree: Limitations

More than one range conditions

where last_name>? and first_name>?

Can’t optimize to the right of the first range conditon

where last_name>? and first_name=?


Clustered Index


Clustered Index

Non Clustered

Clustered

Index organized table

Heap table



Useful Commands


Useful commands

show index from TABLE;

explain [extended] SELECT * FROM TABLE;

UPDATE, DELETE convert to SELECT


Explain

select_tpe

simple, primary, subquery, derived, union

type

all < index < range < ref < eq_ref < const, system < null


Explain

Extra

using where

using index

using filesort

using temporary


Indexing Strategies


Indexing Strategies

Isolate the column

Prefix Indexes and Index Selectivity

Covering Indexes

Use Index Scan For Sorts


Isolate the column

where last_name=”Fred”

where a+1=5

where md5(a)=”45c48cce2e2d7fbdea1afc5”


Prefix index & Index selectivity

Prefix index

KEY index_on_sum(`sum`(5))

Index Selectivity

Cardinality/Count(*)

0..1


Covering Index

select first_name from people where last_name=”fred”

Extra: Using index

Not support “Like” in query


Using Index for Sorts

select * from people where last_name=? and first_name =? order by dob


Redundant/Duplicate index

Duplicate

primary key(id)

key(id)

unique(id)

Redundant

key(a, b, c)

key(a, b)

key(a)

key(b, a)


Others

Index merge

Or

Sub-query/Join/Union

Group/Order

Locking

Query optimization


References

http://www.mysqlperformanceblog.com/

http://www.percona.com/






Questions?


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