This document discusses MySQL indexes. It begins by describing the different storage engines in MySQL, including MyISAM and InnoDB. It then covers InnoDB storage architecture and how InnoDB interacts with the file system. The main types of indexes in MySQL are described as B-tree, hash, R-tree and full-text indexes. B-tree indexes are discussed in more detail, including how they support different query types and their limitations. Other topics covered include clustered indexes, useful index-related commands like EXPLAIN, and indexing strategies.

1. MySQL Index
Andy Yao
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2. MySQL Basic
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3. MySQL Architecture
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4. Storage Engine: MyISAM
Table lock
No automated data recovery
No transactions
Only indexes are cached in memory
Compact storage
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5. Storage Engine: InnoDB
Transactional
Foreign keys
Multiversioning
Clustered by primary key
No cached count(*)
Blocking AUTO_INCREMENT
Optimized cache
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6. 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
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7. 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)
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8. Types of Indexes
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9. Types of Indexes
B+Tree indexes
Hash indexes
R-Tree indexes
Full-text indexes
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10. B+Tree Indexes
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11. Binary search tree
Binary search tree AVL tree
2
6
3
3 7
5
7
2 5 8
6 8
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12. B Tree
25 50 75 ...
5 10 15 20 25 30 50 55 60 65 75 80 85 90
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13. B+Tree
25 50 75 ...
5 10 15 20 25 30 50 55 60 65 75 80 85 90
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14. B+Tree Indexes
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15. 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)
);
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16. B+tree indexes: Demo
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17. 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=?
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18. B+Tree: Types of queries
Match a column prefix
where last_name like ”Liang%”
Match a range of values
where last_name > ?
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19. B+Tree: Types of queries
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=?
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20. B+Tree: Limitations
Doesn’t start from leftmost
where first_name=?
Skip columns in the index
where last_name=? and bod=?
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21. 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=?
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22. Clustered Index
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23. Clustered Index
Non Clustered
Clustered
Index organized table
Heap table
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24. Friday, December 30, 11

25. Useful Commands
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26. Useful commands
show index from TABLE;
explain [extended] SELECT * FROM TABLE;
UPDATE, DELETE convert to SELECT
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27. Explain
select_tpe
simple, primary, subquery, derived, union
type
all < index < range < ref < eq_ref < const,
system < null
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28. Explain
Extra
using where
using index
using filesort
using temporary
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29. Indexing Strategies
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30. Indexing Strategies
Isolate the column
Prefix Indexes and Index Selectivity
Covering Indexes
Use Index Scan For Sorts
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31. Isolate the column
where last_name=”Fred”
where a+1=5
where md5(a)=”45c48cce2e2d7fbdea1afc5”
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32. Prefix index & Index
selectivity
Prefix index
KEY index_on_sum(`sum`(5))
Index Selectivity
Cardinality/Count(*)
0..1
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33. Covering Index
select first_name from people where
last_name=”fred”
Extra: Using index
Not support “Like” in query
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34. Using Index for Sorts
select * from people
where last_name=? and first_name =?
order by dob
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35. Redundant/Duplicate index
Duplicate Redundant
primary key(id) key(a, b, c)
key(id) key(a, b)
unique(id) key(a)
key(b, a)
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36. Others
Index merge
Or
Sub-query/Join/Union
Group/Order
Locking
Query optimization
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37. References
http://www.mysqlperformanceblog.com/
http://www.percona.com/
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38. Questions?
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