A Brief Introduction to MySQL

By Nishkam, Neeraj,Saurabh, Hrishikesh and Somesh

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

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 ).

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.

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.

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’

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

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

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

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

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

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.

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

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

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.

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

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 .

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

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 MyISAMANALYZE During analysis the table is locked with a

read lock

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

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)

• 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)

• 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)

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