1. MySQL Index
Andy Yao
Friday, December 30, 11

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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