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? ď Ź ď Ź
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 ?
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 MyISAM ANALYZE 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