MySQL 简要介绍 http://www.ossez.com/forum.php?mod=viewthread&tid=26870&fromuid=426 (出处: OSSEZ)

1. A Brief Introduction to MySQL
By Nishkam,
Neeraj,Saurabh,
Hrishikesh and
Somesh

2. Pointers
 What is MySQL ? Its good features.
 Installation guide.
 Security and Privilege System
 Compatibility with standards
 Locks – an interesting feature
 Table types
 Some more salient features
 Replication

3. What Is MySQL?
 A fast, reliable, easy-to-use, multi-user multi-
threaded relational database system.
 It is freely available and released under GPL
(GNU General Public License ).

4. Why Use MySQL ?
 MySQL server can handle very large
databases.
 Offers rich and very useful set of functions.
 Connectivity, speed and security make MySQL
very suited for accessing database on a
network.
 A lot of contributed software available.

5. What Does MySQL Offer ?
 A privilege and password system that is very
flexible and secure and allows host-based
verification.
 Multi-threaded request-handling using kernel
thread.
 Replication features.
 Very actively developed.
 Memory leak proof.

6. Quick Installation Guide
• tar –zxvf Mysql.x.xx.xx.tar.gz
 cd Mysql-x.xx.xx.xx
 ./configure –prefix=/usr/local/mysql
 make
 make install
 scripts/mysql_install_db
 safe_mysqld
 Mysql –u root password ‘mypassword’

7. Configuring MySql
 --bindir=Dir specifies dir for binaries
 --localstatedir=Dir data dir
 --with-tcp-port=portno
 --with-unix-sock-path=absolute-path
 --with-mysqld-ldflag=-all-static
 --with-charset=charset (default Latin1)
 --with-low-memory

8. Support
 Works on many different platforms like
FreeBSD , NetBSD , Linux 2.0+, Windows ’95,
’98, 2000 & NT, HP-UX etc
 There are client tools and APIs available in c,
c++, java, perl, python, php, Tcl

9. Security in mysql
 Issues that bother: eavesdropping,altering
 Uses ACL’s (Access Control Lists) , also
there’s some support for SSL connections
 Has inbuilt methods for storing confidential
data like passwords in encrypted form.
 Access is restricted thru grant of privileges to
users,hosts

10. Privileges provided by mysql
 The five tables:
user,db,host,tables_priv,columns_priv
 The privileges come into play only if there is a
retrieval of data from the database, or updation
of data in the database,e.g:
select 1+1; calculator 
 File privilege : load data infile, select …. Into
outfile

11. How the privilege system works
 First reference to user followed by db and host , takes
place during connection verification
 Reference to tables_priv and columns_priv at data
access stage
 Ordering of user table on the basis of more specific
host values first, followed by more specific user values.
 For security purposes , mysql disallows host
addresses of the form :192.168.7.yahoo.com

12. Some tips on security
 Beneficial to invest in a firewall ; check using “telnet
server_port 3306”
 Do not rely on the data entered by the user, he can
trick the code by using special character sequences
 Make use of tcpdump, to check the whether or not
mysql data streams r unencrypted:
tcpdump –l –i eth0 –w – src port 3306|strings
 Dont run mysqld as root.
 Don’t give process and file privileges to users as far as
possible.

13. Continued…..
 Following mysqld options affect security:
1. –- secure 2. – skip-grant-privileges
3. – skip-name-resolve 4. –skip-networking
 Passwords by default are stored in hashed form in
database.But if the scrambled password is known the
hacker can still log in as the user.
 Passwords can be stored in my.cnf file when
non-interactive access has to be done
 Inbuilt functions for hashing: password,
encrypt,encode,decode

14. Compatibility with Standards
What doesn’t MySQL have ?
 Transactions – no provision for commit and
rollback
 No nested sub-queries
 Views are not supported
 Foreign keys not used for referential integrity
checks

15. Compatibility (contd.)
What extra does MySQL have ?
 Locking/Unlocking of tables
 Atomicity of operations
 Directory organization
 Access of tables across tables
 Several other features, discussed later…

16. More about Locks !
 Locks help in maintaining integrity, atomicity
 Read locks – enable you to only read from the
locked tables.
 Write locks – enable you to read and write
exclusively. Other threads can’t access/update
currently locked tables
 Write locks have higher priority than read locks

17. MySql Table Types
 Creates a .frm file that holds the table and column definition.
 Syntax for defining table type is .. :
CREATE TABLE test ( )
TYPE=HEAP ..
 Categorization of types : Transaction safe type and Non
transaction safe type.
 Transaction Safe table types allow rollbacks,restore changes if
update fails ,etc .
 Non Transaction Safe table types are much faster ,use less
disk space as well as memory for updates.

18. MyISAM tables
 Use B-Tree indexing to store the keys, string indexes
are compressed .
 MyISAM itself supports three different table formats: a)
static (fixed length) b) Dynamic c) Compressed
 Static : fastest ,secure and simplest format ,
used when there are no varchar, blob or text.
 Dynamic : each record stores a header that contain its
length
 Compressed : created using myisampack tool , they
are read only ,use very little space as each record is
compressed separately
 ISAM is a deprecated version of MyISAM

19. Merge tables
 A collection of identical MyISAM tables which are used
collectively.
 FOR eg :
CREATE TABLE t1 (a INT AUTO_INCREMENT
PRIMARY KEY, message CHAR(20));
CREATE TABLE t2 (a INT AUTO_INCREMENT
PRIMARY KEY, message CHAR(20)) ;
CREATE TABLE total (a INT NOT NULL, message
CHAR(20), KEY(a)) TYPE=MERGE UNION=(t1,t2)
• allowed : select ,insert and Operations update .

20. Heap tables and Berkley DB
 Use hashed index and are stored in memory
 Generally used for temporary tables .
•Berkley DB is used for making the tables
transaction safe

21. MySQL Language Reference
OPTIMIZE
 Syntax :: … OPTIMIZE TABLE tbl_name[,tbl_name]..
 Used only for MyISAM tables
 It performs the following functions :repairs the table if the table has
deleted rows,sorts the index,and the statistics are also made to
date.
CHECK
 Syntax :: … CHECK
TABLE tbl_name[,tbl_name...] [TYPE = [QUICK | FAST | EXTEND
| CHANGED]]

22. MySQL Language Reference
 Checks a table for errors and updates the key
statistics of the table
BACKUP
 BACKUP TABLE tbl_name[,tbl_name...] TO
'/path/to/backup/directory‘
 This again works only for MyISAM
ANALYZE
 During analysis the table is locked with a read
lock

23. MySQL Language Reference
REPAIR
 Syntax:
REPAIR TABLE tbl_name[,tbl_name...] [TYPE = QUICK]
FLUSH
 Syntax :
FLUSH flush_option [,flush_option]
 Used to clear the internal cache of Mysql
 It has various options like HOSTS,LOGS,PRIVELEDGES,
TABLES tbl_names,etc

24. Replication in MySQL
 What??
 One server is designated as the master, while the other
( or others) as slave(s)
 Updates done only on master and binary logs made
 The slave connects to the master, catches up on the
missed updates, and then starts receiving updates
immediately as they come to the master.
 Why??
 For robustness you have two systems and switch to
the backup if you have problems with the master.
 The extra speed is achieved by sending a part of the
non-updating queries to the replica server.

25. How To (SLAVE)
• Upgrade both slave and master to 3.23.15 or higher.
• PUT THESE IN my.cnf of SLAVE
• master-host,user,passwd
• server-id=< unique no>= 1 & <=2^32-1
• master-connect-retry !! (keep trying)
• master-info-file
• replicate-rewrite-db
• skip-slave-start
• Restart the slave(s)

26. How To (SLAVE) (contd)
• Take a snapshot of all the tables/databases on
the master
• Use command LOAD TABLE <tblname>
FROM MASTER (3.23.23)+
 SLAVE START/STOP
 FLUSH SLAVE

27. HOW TO (MASTER)
 log-bin , FLUSH MASTER , FLUSH SLAVE
 When you start the slave thread will be created
 Tables are not Locked
 SET SQL_LOG_BIN=0/1
 CHANGE MASTER TO master_def_list