Step 0 How to begin and what you need to do before you start?

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1 Written and cooked by Janusz R. Getta, School of Computing and Information Technology, University of Wollongong Building 3, room 2120, ext 4339, jrg ËÁ̽½ Ø Å Ò Ñ ÒØ Ò Ë ÙÖ ØÝ Ê Ô º¾ ÀÓÛ ØÓ Ø ÖÚ Ö Ý Ø Ñ Ú Ö Ð Table of contents Step 0 How to begin and what you need to do before you start? Step 1 How to find the current values of server system variables? Step 2 How to change the values of server system variables with SET statement? Step 3 How to change the values of server system variables in a system configuration file? Step 0 How to begin and what you need to do before you start? A printable copy of this experiment in pdf format is available here ( e8-2.pdf). If you have not done it yet then perform the following actions. Logon to your Win 7 system and start VirtualBox. Next, either import your appliance from your USB drive and start imported virtual machine or use one of the brand new virtual machines available on your Win 7 system. Logon to Ubuntu operating system as csit115 user. Start Terminal icon to open Terminal application. We use command line interface to communicate with MySQL database server. The server system variables determine the behaviour of MySQL database server. The values of system variables are set can be at server startup time either in a server startup command line or in an option file. Majority (but not all!) can be dynamically changed while the server is runnin. Some of the variables require the server to be stopped and restarted later on. SET statement, which enables you to modify operation of the server without having to stop and restart it. There are two types of system variables: global variables and session variables. Global variables are valid at any moment of any database session (connection). Session variables are valid only for a period of a single session (connection). When a database server starts then it initializes its global variables either from the default values or from command line or from a configuration file. A collection of session variables is maintained for each connection. Session variables are initialized at stratup time from the val;ues of respective global variables. Step 1 How to find the current values of server system variables? Start Terminal and in Terminal window connect to MySQL in the following way. mysql -p -v -u csit115 To find the current values of server system variables we use a statement SHOW VARIABLES. SHOW VARIABLES; The statement lists the names of all server veraiables tiogether with their values. The first few variables are listed below. SHOW VARIABLES 1

2 auto_increment_increment 1 auto_increment_offset 1 autocommit ON automatic_sp_privileges ON avoid_temporal_upgrade OFF version version_comment MySQL Community Server version_compile_machine i686 version_compile_os Linux wait_timeout warning_count rows in set (0.00 sec) Tolist a name and value of a particular variable or a group of variables we use LIKE clause with SHOW VARIABLES statement. For example to list the values of all parameters controlling InnoDB storage engine we use the following statement. SHOW VARIABLES LIKE innodb% ; SHOW VARIABLES LIKE innodb% innodb_adaptive_flushing ON innodb_adaptive_flushing_lwm 10 innodb_adaptive_hash_index ON innodb_adaptive_hash_index_parts 8 innodb_adaptive_max_sleep_delay innodb_version innodb_write_io_threads rows in set (0.04 sec) SHOW VARIABLES statement when used without GLOBAL or LOCAL keyword always lists SESSION values. Step 2 How to change the values of server system variables with SET statement? Dynamic server system variables can be change with SET GLOBAL or SET SESSION commands. In this set we shall examine a value of autocommit variable and we shall set its SESSION value to 1. It means that each modification will be automatically committed immediatelly after every data manipulation operation. 2

3 First, use a statement SHOW VARIABLES LIKE autocommit ; to find what is the present value of the variable. SHOW VARIABLES LIKE autocommit ; autocommit ON 1 row in set (0.05 sec) As expected, the present value of autocommit variable is ON It means that modifications are automatically committed immediately after each data manipulation statement COMMIT statement. To verify that modifications are committed immediate after each data manipulation operation we create a small relational table and we insert a single row into the table. USE csit115; CREATE TABLE Q(A CHAR(5)); INSERT INTO Q VALUES( ); Next, we try to rollback the insertion with ROLLBACK statement. ROLLBACK; To verify if the insertion could be rolled back we list the contents of the relational table. SELECT * FROM Q; A The relational table is not empty, hence rollback was impossible due to commit perfromed immediately after INSERT statement. To change SESSION value of autocommit variable execute the following statement. SET SESSION autocommit= OFF ; And repeat SHOW VARIABLES LIKE autocommit ; to find the current value of autocommit variable. 3

4 autocommit OFF 1 row in set (0.00 sec) Next, make a sample relational table empty and list the contents of the table. DELETE FROM Q; SELECT * FROM Q; Empty set (0.00 sec) Next, roll back the deletions above. ROLLBACK; The contents of the relational tables is the following. SELECT * FROM Q; A row in set (0.00 sec) The latest ROLLBACK statement rolled back the deletions. It means that the latest DELETE statement has not been automatically committed immediately after its processing. If you exit mysql client and you logon one more a value of system variable autocommitreturns to its original value, i.e. ON. This is because all SET statements above have been processed with a clause SESSION. To clean after the experiment drop a relational table Q and quit mysql client. Step 3 How to change the values of server system variables in a system configuration file? This action we change a value of server system variable autocommit in a system configuration file. If you have not done it yet then start Terminal application. In this action we use command line interface to communicatewith MySQL database server. To find the possible locations of system configuration file execute the following command in Terminal window. mysql --help grep "Default options" -A 1 The system displays the following possible locations. Default options are read from the following files in the given order: /etc/my.cnf /etc/mysql/my.cnf /.my.cnf 4

5 On our installation of MySQL a system configuration file is located at /etc/mysql/mysql.conf.d and a name of the file is mysqld.cnf. To edit the file execute the following commands in Terminal window. cd /etc/mysql/mysql.conf.d gedit mysqld.cnf At the moment the contents of a system configuration file is the following. Copyright (c) 2014, 2016, Oracle and/or its affiliates. All rights reserved. This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; version 2 of the License. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA USA The MySQL Server configuration file. For explanations see [mysqld] pid-file = /var/run/mysqld/mysqld.pid socket = /var/run/mysqld/mysqld.sock datadir = /var/lib/mysql log-error = /var/log/mysql/error.log By default we only accept connections from localhost bind-address = Disabling symbolic-links is recommended to prevent assorted security risks symbolic-links = 0 Enforce foreign key constraints foreign_key_checks = ON Make table names case sensitive lower_case_table_names = 0 Enforce ANSI Standard of SQL sql-mode = ANSI Do not need to use keys in WHERRE clause sql_safe_updates = 1 INSERT statements produce warnings sql_warnings = 1 At the end of the file add the following to lines and save the file. Turn autocommit OFF 5

6 autocommit = 0 Now to enforce the modifications shutdown and restart MySQL database server. It is explained in Recipe 8.1 how to it. When ready start mysql client and connect to the server. Disply the present value of autocommit variable. SHOW VARIABLES like autocommit ; You should get the following results. autocommit OFF 1 row in set (0.04 sec) References MySQL 5.7 Reference Manual, Server System Variables ( MySQL 5.7 Reference Manual, Using System Variables ( MySQL 5.7 Reference Manual, SHOW Syntax ( MySQL 5.7 Reference Manual, SET Syntax ( 6