Mysql index

MySQL Index
Andy 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 Segment
leaf node segment
extent extent

non-leaf node segment
extent extent
rollback node segment

...

Extent
Row
Page
trx id
row row
row id
row row
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

Binary search tree AVL tree

2
6

3

3 7
5

7
2 5 8

6 8


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: 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 Redundant

primary key(id) key(a, b, c)

key(id) key(a, b)

unique(id) 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?


Mysql index

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