Transcript What Is MySql? - CSE, IIT Bombay

A Brief Introduction to MySQL
By Nishkam,
Neeraj,Saurabh,
Hrishikesh and
Somesh
Pointers
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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
What Is MySQL?
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A fast, reliable, easy-to-use, multi-user multithreaded relational database system.
It is freely available and released under GPL
(GNU General Public License ).
Why Use MySQL ?
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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.
What Does MySQL Offer ?
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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.
Quick Installation Guide
• tar –zxvf Mysql.x.xx.xx.tar.gz
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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’
Configuring MySql
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--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
Support
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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
Security in mysql
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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
Privileges provided by mysql
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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
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
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Some tips on security
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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.
Continued…..
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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
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
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…
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
MySql Table Types
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Creates a .frm file that holds the table and column definition.
Syntax for defining table type is .. :
CREATE TABLE test (
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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.
MyISAM tables
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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
Merge tables
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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 .
Heap tables and Berkley DB
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Use hashed index and are stored in memory
Generally used for temporary tables .
• Berkley DB is used for making the tables
transaction safe
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]]
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
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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
Replication in MySQL
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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.
How To (SLAVE)
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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)
How To (SLAVE) (contd)
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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
HOW TO (MASTER)
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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