The myisam storage engine in version 4.1 was already mature enough to allow a direct upgrade to the next major version of MySQL.

For this step two shells are required because locks belong to the mysql session.

# quickpkg dev-db/mysql
# alias MYSQL="mysql --user=root --password='your_password'"
# DATADIR=$(MYSQL --batch --raw --silent --skip-column-names \
     --execute='SHOW variables LIKE "datadir";' \
     | sed -e 's|datadir[ \t]||')

(This next step should be done in the second shell)
# mysql --user=root --password='your_password'
mysql> FLUSH TABLES WITH READ LOCK;

(Return to the first shell to run this command)
# tar -cjpvf ~/mysql.$(date +%F"T"%H-%M).tar.bz2 \
     /etc/conf.d/mysql /etc/mysql/my.cnf "${DATADIR}"

(The following commands should be done in the second shell)
mysql> UNLOCK TABLES;
mysql> quit

(Return to the first shell for the rest of the upgrade)
# tar -tjvf ~/mysql.*.tar.bz2
# emerge -av ">dev-db/mysql-5.0"
# dispatch-conf
# revdep-rebuild
# /etc/init.d/mysql restart
# mysql_upgrade_shell --user=root --password='your_password' \
     --protocol=tcp --datadir="${DATADIR}"
# /etc/init.d/mysql restart
# unset DATADIR
# unalias MYSQL

Users upgrading from an old version (<4.0.24) of MySQL will first have to install MySQL 4.0.25. If you are already running a more recent version, you can skip this section and continue with the next one.

# emerge -av --buildpkg "<mysql-4.1"

One of the most important tasks that every database administrator has to perform is backing up data. Here we go:

# mysqldump \
  -uroot \
  --password='your_password' \
  -hlocalhost \
  --all-databases \
  --opt \
  --allow-keywords \
  --flush-logs \
  --hex-blob \
  --master-data \
  --max_allowed_packet=16M \
  --quote-names \
  --result-file=BACKUP_MYSQL_4.0.SQL

Now a file named BACKUP_MYSQL_4.0.SQL should exist, which can be used later to recreate your data. The data is described in the MySQL dialect of SQL, the Structured Query Language.

Now would also be a good time to see if the backup you have created is working.

If you have skipped step #1, you now have to create a backup package (of the database server, not the data) of the currently installed version:

# quickpkg dev-db/mysql

Now it's time to clean out the current version and all of its data:

# /etc/init.d/mysql stop
# emerge -C mysql
# tar cjpvf ~/mysql.$(date +%F"T"%H-%M).tar.bz2 /etc/mysql/my.cnf /var/lib/mysql/
# ls -l ~/mysql.*
# rm -rf /var/lib/mysql/ /var/log/mysql

After you get rid of your old MySQL installation, you can now install the new version. Note that revdep-rebuild is necessary for rebuilding packages linking against MySQL.

# emerge -av ">mysql-4.1"
(Update your config files, you may also use dispatch-conf)
# etc-update
# revdep-rebuild

Now configure the newly installed version of MySQL and restart the daemon:

# emerge --config =mysql-4.1.<micro_version>
# /etc/init.d/mysql start

Finally you can import the backup you have created during step #2.

Older mysqldump utilities may export tables in the wrong order when foreign keys are involved. To work around this problem, surround the SQL with the following statements:

SET FOREIGN_KEY_CHECKS=0
SET FOREIGN_KEY_CHECKS=1

Next, import the backup.

# cat BACKUP_MYSQL_4.0.SQL \
     | mysql \
     -uroot \
     --password='your_password' \
     -hlocalhost \
     --max_allowed_packet=16M

# mysql_fix_privilege_tables \
     --defaults-file=/etc/mysql/my.cnf \
     --user=root \
     --password='your_password'

If you restart your MySQL daemon now and everything goes as expected, you have a fully working version of 4.1.x.

# /etc/init.d/mysql restart

If you encountered any problems during the upgrade process, please report them on Bugzilla.

If you are not happy with MySQL 4.1, it's possible to go back to MySQL 4.0.

# /etc/init.d/mysql stop
# emerge -C mysql
# rm -rf /var/lib/mysql/ /var/log/mysql
# emerge --usepkgonly "<mysql-4.1"
(Replace <timestamp> with the one used when creating the backup.)
# tar -xjpvf mysql.<timestamp>.tar.bz2 -C /
# /etc/init.d/mysql start

This chapter is not intended to be an exhaustive guide on how to do such conversions, rather a short list of hints on which the reader can elaborate.

Converting a database may be a complex task and difficulty increases with data variancy. Things like serialized object and blobs are one example where it's difficult to keeps pieces together.

Every utf-8 character is considered 3 bytes long within an index. Indexes in MySQL can be up to 1000 bytes long (767 bytes for InnoDB tables). Note that the limits are measured in bytes, whereas the length of a column is interpreted as number of characters.

MySQL can also create indexes on parts of a column, this can be of some help. Below are some examples:

$ mysql -uroot -p'your_password' test

mysql> SHOW variables LIKE "version" \G
*************************** 1. row ***************************
Variable_name: version
    Value: 5.0.24-log
1 row in set (0.00 sec)

mysql> CREATE TABLE t1 (
  ->   c1 varchar(255) NOT NULL default '',
  ->   c2 varchar(255) NOT NULL default ''
  ->   ) ENGINE=MyISAM DEFAULT CHARSET=utf8;
Query OK, 0 rows affected (0.01 sec)

mysql> ALTER TABLE t1
  ->   ADD INDEX idx1 ( c1 , c2 );
ERROR 1071 (42000): Specified key was too long; max key length is 1000 bytes

mysql> ALTER TABLE t1
  ->   ADD INDEX idx1 ( c1(165) , c2(165) );
Query OK, 0 rows affected (0.01 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> CREATE TABLE t2 (
  ->   c1 varchar(255) NOT NULL default '',
  ->   c2 varchar(255) NOT NULL default ''
  ->   ) ENGINE=MyISAM DEFAULT CHARSET=sjis;
Query OK, 0 rows affected (0.00 sec)

mysql> ALTER TABLE t2
  ->   ADD INDEX idx1 ( c1(250) , c2(250) );
Query OK, 0 rows affected (0.03 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> CREATE TABLE t3 (
  ->   c1 varchar(255) NOT NULL default '',
  ->   c2 varchar(255) NOT NULL default ''
  ->   ) ENGINE=MyISAM DEFAULT CHARSET=latin1;
Query OK, 0 rows affected (0.00 sec)

mysql> ALTER TABLE t3
  ->   ADD INDEX idx1 ( c1 , c2 );
Query OK, 0 rows affected (0.03 sec)
Records: 0  Duplicates: 0  Warnings: 0

The system must be configured to support the UTF-8 locale. You will find more information in our Using UTF-8 with Gentoo and Localization Guide documents.

In this example, we set some shell environment variables to make use of the English UTF-8 locale in /etc/env.d/02locale:

LC_ALL=en_US.UTF-8
LANG=en_US.UTF-8

Be sure to run env-update && source /etc/profile afterward.

iconv, provided by sys-libs/glibc, is used to convert text files from one charset to another. The app-text/recode package can be used as well.

(From latin1 to utf8)
$ iconv -f ISO-8859-15 -t UTF-8 file1.sql > file2.sql

(From Japanese to utf8)
$ iconv -f ISO2022JP -t UTF-8 file1.sql > file2.sql

iconv can be used to recode a sql dump even if the environment is not set to utf8.

It's possible to use the CONVERT() and CAST() MySQL functions to convert data in your SQL scripts.

To use utf-8 with apache, you need to adjust the following variables in httpd.conf: AddDefaultCharset, CharsetDefault, CharsetSourceEnc. If your source html files aren't encoded in utf-8, they must be converted with iconv or recode.