Source:http://dev.mysql.com/doc/refman/4.1/en/mysqlcheck.html

The mysqlcheck client checks, repairs, optimizes, and analyzes tables. mysqlcheck is available as of MySQL 3.23.38.

mysqlcheck is similar in function to myisamchk, but works differently. The main operational difference is that mysqlcheck must be used when the mysqld server is running, whereas myisamchk should be used when it is not. The benefit of using mysqlcheck is that you do not have to stop the server to check or repair your tables.

mysqlcheck uses the SQL statements CHECK TABLE, REPAIR TABLE, ANALYZE TABLE, and OPTIMIZE TABLE in a convenient way for the user. It determines which statements to use for the operation you want to perform, and then sends the statements to the server to be executed. For details about which storage engines each statement works with, see the descriptions for those statements in Chapter 12, SQL Statement Syntax.

The MyISAM storage engine supports all four statements, so mysqlcheck can be used to perform all four operations on MyISAM tables. Other storage engines do not necessarily support all operations. In such cases, an error message is displayed. For example, if test.t is a MEMORY table, an attempt to check it produces this result:

shell> mysqlcheck test t
test.t
note     : The storage engine for the table doesn't support check

Caution

It is best to make a backup of a table before performing a table repair operation; under some circumstances the operation might cause data loss. Possible causes include but are not limited to filesystem errors.

There are three general ways to invoke mysqlcheck:

shell> mysqlcheck [options] db_name [tables]
shell> mysqlcheck [options] --databases db_name1 [db_name2 db_name3...]
shell> mysqlcheck [options] --all-databases

If you do not name any tables following db_name or if you use the --databases or --all-databases option, entire databases are checked.

mysqlcheck has a special feature compared to other client programs. The default behavior of checking tables (--check) can be changed by renaming the binary. If you want to have a tool that repairs tables by default, you should just make a copy of mysqlcheck named mysqlrepair, or make a symbolic link to mysqlcheck named mysqlrepair. If you invoke mysqlrepair, it repairs tables.

The following names can be used to change mysqlcheck default behavior:

mysqlrepair

The default option is --repair

mysqlanalyze

The default option is --analyze

mysqloptimize

The default option is --optimize

mysqlcheck supports the following options:

• --help, -?

  Display a help message and exit.

• --all-databases, -A

  Check all tables in all databases. This is the same as using the --databases option and naming all the databases on the command line.

• --all-in-1, -1

  Instead of issuing a statement for each table, execute a single statement for each database that names all the tables from that database to be processed.

• --analyze, -a

  Analyze the tables.

  MySQL Enterprise. For expert advice on optimizing tables, subscribe to the MySQL Enterprise Monitor. For more information, see http://www.mysql.com/products/enterprise/advisors.html.

• --auto-repair

  If a checked table is corrupted, automatically fix it. Any necessary repairs are done after all tables have been checked.

• --character-sets-dir=path

  The directory where character sets are installed. See Section 9.2, “The Character Set Used for Data and Sorting”.

• --check, -c

  Check the tables for errors. This is the default operation.

• --check-only-changed, -C

  Check only tables that have changed since the last check or that have not been closed properly.

• --compress

  Compress all information sent between the client and the server if both support compression.

• --databases, -B

  Process all tables in the named databases. Normally, mysqlcheck treats the first name argument on the command line as a database name and following names as table names. With this option, it treats all name arguments as database names.

• --debug[=debug_options], -# [debug_options]

  Write a debugging log. A typical debug_options string is often 'd:t:o,file_name'.

• --default-character-set=charset_name

  Use charset_name as the default character set. See Section 9.2, “The Character Set Used for Data and Sorting”.

• --extended, -e

  If you are using this option to check tables, it ensures that they are 100% consistent but takes a long time.

  If you are using this option to repair tables, it runs an extended repair that may not only take a long time to execute, but may produce a lot of garbage rows also!

• --fast, -F

  Check only tables that have not been closed properly.

• --force, -f

  Continue even if an SQL error occurs.

• --host=host_name, -h host_name

  Connect to the MySQL server on the given host.

• --medium-check, -m

  Do a check that is faster than an --extended operation. This finds only 99.99% of all errors, which should be good enough in most cases.

• --optimize, -o

  Optimize the tables.

• --password[=password], -p[password]

  The password to use when connecting to the server. If you use the short option form (-p), you cannot have a space between the option and the password. If you omit the password value following the --password or -p option on the command line, you are prompted for one.

  Specifying a password on the command line should be considered insecure. See Section 5.6.6, “Keeping Passwords Secure”.

• --pipe, -W

  On Windows, connect to the server via a named pipe. This option applies only for connections to a local server, and only if the server supports named-pipe connections.

• --port=port_num, -P port_num

  The TCP/IP port number to use for the connection.

• --protocol={TCP|SOCKET|PIPE|MEMORY}

  The connection protocol to use for connecting to the server. It is useful when the other connection parameters normally would cause a protocol to be used other than the one you want. For details on the allowable values, see Section 4.2.2, “Connecting to the MySQL Server”. This option was added in MySQL 4.1.

• --quick, -q

  If you are using this option to check tables, it prevents the check from scanning the rows to check for incorrect links. This is the fastest check method.

  If you are using this option to repair tables, it tries to repair only the index tree. This is the fastest repair method.

• --repair, -r

  Perform a repair that can fix almost anything except unique keys that are not unique.

• --silent, -s

  Silent mode. Print only error messages.

• --socket=path, -S path

  For connections to localhost, the Unix socket file to use, or, on Windows, the name of the named pipe to use.

• --ssl*

  Options that begin with --ssl specify whether to connect to the server via SSL and indicate where to find SSL keys and certificates. See Section 5.6.7.3, “SSL Command Options”.

• --tables

  Overrides the --databases or -B option. All name arguments following the option are regarded as table names.

• --use-frm

  For repair operations on MyISAM tables, get the table structure from the .frm file so that the table can be repaired even if the .MYI header is corrupted. This option was added in MySQL 4.0.5.

• --user=user_name, -u user_name

  The MySQL user name to use when connecting to the server.

• --verbose, -v

  Verbose mode. Print information about the various stages of program operation.

• --version, -V

  Display version information and exit.

Source: http://dev.mysql.com/doc/refman/5.1/en/forcing-recovery.html 

If there is database page corruption, you may want to dump your tables from the database with SELECT INTO ... OUTFILE. Usually, most of the data obtained in this way is intact. However, it is possible that the corruption might cause SELECT * FROM tbl_name statements or InnoDB background operations to crash or assert, or even cause InnoDB roll-forward recovery to crash. In such cases, you can use the innodb_force_recovery option to force the InnoDB storage engine to start up while preventing background operations from running, so that you are able to dump your tables. For example, you can add the following line to the [mysqld] section of your option file before restarting the server:

[mysqld]
innodb_force_recovery = 4

innodb_force_recovery is 0 by default (normal startup without forced recovery) The allowable non-zero values for innodb_force_recovery follow. A larger number includes all precautions of smaller numbers. If you are able to dump your tables with an option value of at most 4, then you are relatively safe that only some data on corrupt individual pages is lost. A value of 6 is more drastic because database pages are left in an obsolete state, which in turn may introduce more corruption into B-trees and other database structures.

• 1 (SRV_FORCE_IGNORE_CORRUPT)

  Let the server run even if it detects a corrupt page. Try to make SELECT * FROM tbl_name jump over corrupt index records and pages, which helps in dumping tables.

• 2 (SRV_FORCE_NO_BACKGROUND)

  Prevent the main thread from running. If a crash would occur during the purge operation, this recovery value prevents it.

• 3 (SRV_FORCE_NO_TRX_UNDO)

  Do not run transaction rollbacks after recovery.

• 4 (SRV_FORCE_NO_IBUF_MERGE)

  Prevent insert buffer merge operations. If they would cause a crash, do not do them. Do not calculate table statistics.

• 5 (SRV_FORCE_NO_UNDO_LOG_SCAN)

  Do not look at undo logs when starting the database: InnoDB treats even incomplete transactions as committed.

• 6 (SRV_FORCE_NO_LOG_REDO)

  Do not do the log roll-forward in connection with recovery.

The database must not otherwise be used with any non-zero value of innodb_force_recovery. As a safety measure, InnoDB prevents users from performing INSERT, UPDATE, or DELETE operations when innodb_force_recovery is greater than 0.

You can SELECT from tables to dump them, or DROP or CREATE tables even if forced recovery is used. If you know that a given table is causing a crash on rollback, you can drop it. You can also use this to stop a runaway rollback caused by a failing mass import or ALTER TABLE. You can kill the mysqld process and set innodb_force_recovery to 3 to bring the database up without the rollback, then DROP the table that is causing the runaway rollback.

Source: http://dev.mysql.com/doc/refman/5.1/en/repair.html

The discussion in this section describes how to use myisamchk on MyISAM tables (extensions .MYI and .MYD).

You can also (and should, if possible) use the CHECK TABLE and REPAIR TABLE statements to check and repair MyISAM tables. See Section 12.5.2.3, “CHECK TABLE Syntax”, and Section 12.5.2.6, “REPAIR TABLE Syntax”.

Symptoms of corrupted tables include queries that abort unexpectedly and observable errors such as these:

• tbl_name.frm is locked against change

• Can’t find file tbl_name.MYI (Errcode: nnn)

• Unexpected end of file

• Record file is crashed

• Got error nnn from table handler

To get more information about the error, run perror nnn, where nnn is the error number. The following example shows how to use perror to find the meanings for the most common error numbers that indicate a problem with a table:

shell> perror 126 127 132 134 135 136 141 144 145
MySQL error code 126 = Index file is crashed
MySQL error code 127 = Record-file is crashed
MySQL error code 132 = Old database file
MySQL error code 134 = Record was already deleted (or record file crashed)
MySQL error code 135 = No more room in record file
MySQL error code 136 = No more room in index file
MySQL error code 141 = Duplicate unique key or constraint on write or update
MySQL error code 144 = Table is crashed and last repair failed
MySQL error code 145 = Table was marked as crashed and should be repaired

Note that error 135 (no more room in record file) and error 136 (no more room in index file) are not errors that can be fixed by a simple repair. In this case, you must use ALTER TABLE to increase the MAX_ROWS and AVG_ROW_LENGTH table option values:

ALTER TABLE tbl_name MAX_ROWS=xxx AVG_ROW_LENGTH=yyy;

If you do not know the current table option values, use SHOW CREATE TABLE.

For the other errors, you must repair your tables. myisamchk can usually detect and fix most problems that occur.

The repair process involves up to four stages, described here. Before you begin, you should change location to the database directory and check the permissions of the table files. On Unix, make sure that they are readable by the user that mysqld runs as (and to you, because you need to access the files you are checking). If it turns out you need to modify files, they must also be writable by you.

This section is for the cases where a table check fails (such as those described in Section 6.4.2, “How to Check MyISAM Tables for Errors”), or you want to use the extended features that myisamchk provides.

The options that you can use for table maintenance with myisamchk are described in Section 4.6.3, “myisamchk — MyISAM Table-Maintenance Utility”.

If you are going to repair a table from the command line, you must first stop the mysqld server. Note that when you do mysqladmin shutdown on a remote server, the mysqld server is still alive for a while after mysqladmin returns, until all statement-processing has stopped and all index changes have been flushed to disk.

Stage 1: Checking your tables

Run myisamchk *.MYI or myisamchk -e *.MYI if you have more time. Use the -s (silent) option to suppress unnecessary information.

If the mysqld server is stopped, you should use the --update-state option to tell myisamchk to mark the table as “checked.”

You have to repair only those tables for which myisamchk announces an error. For such tables, proceed to Stage 2.

If you get unexpected errors when checking (such as out of memory errors), or if myisamchk crashes, go to Stage 3.

Stage 2: Easy safe repair

First, try myisamchk -r -q tbl_name (-r -q means “quick recovery mode”). This attempts to repair the index file without touching the data file. If the data file contains everything that it should and the delete links point at the correct locations within the data file, this should work, and the table is fixed. Start repairing the next table. Otherwise, use the following procedure:

1. Make a backup of the data file before continuing.

2. Use myisamchk -r tbl_name (-r means “recovery mode”). This removes incorrect rows and deleted rows from the data file and reconstructs the index file.

3. If the preceding step fails, use myisamchk –safe-recover tbl_name. Safe recovery mode uses an old recovery method that handles a few cases that regular recovery mode does not (but is slower).

Note

If you want a repair operation to go much faster, you should set the values of the sort_buffer_size and key_buffer_size variables each to about 25% of your available memory when running myisamchk.

If you get unexpected errors when repairing (such as out of memory errors), or if myisamchk crashes, go to Stage 3.

Stage 3: Difficult repair

You should reach this stage only if the first 16KB block in the index file is destroyed or contains incorrect information, or if the index file is missing. In this case, it is necessary to create a new index file. Do so as follows:

1. Move the data file to a safe place.

2. Use the table description file to create new (empty) data and index files:

   shell> mysql db_name
   mysql> SET autocommit=1;
   mysql> TRUNCATE TABLE tbl_name;
   mysql> quit

3. Copy the old data file back onto the newly created data file. (Do not just move the old file back onto the new file. You want to retain a copy in case something goes wrong.)

Important

If you are using replication, you should stop it prior to performing the above procedure, since it involves filesystem operations, and these are not logged by MySQL.

Go back to Stage 2. myisamchk -r -q should work. (This should not be an endless loop.)

You can also use the REPAIR TABLE tbl_name USE_FRM SQL statement, which performs the whole procedure automatically. There is also no possibility of unwanted interaction between a utility and the server, because the server does all the work when you use REPAIR TABLE. See Section 12.5.2.6, “REPAIR TABLE Syntax”.

Stage 4: Very difficult repair

You should reach this stage only if the .frm description file has also crashed. That should never happen, because the description file is not changed after the table is created:

1. Restore the description file from a backup and go back to Stage 3. You can also restore the index file and go back to Stage 2. In the latter case, you should start with myisamchk -r.

2. If you do not have a backup but know exactly how the table was created, create a copy of the table in another database. Remove the new data file, and then move the .frm description and .MYI index files from the other database to your crashed database. This gives you new description and index files, but leaves the .MYD data file alone. Go back to Stage 2 and attempt to reconstruct the index file.

Source: http://www.v-nessa.net/2007/07/20/upgrading-to-mysql-5120-on-cpanel 

If you have server that run on cPanel, you’ll probably know how big of a Nazi it is in regards to the MySQL versions it can run. We just got this new line of servers at work and one of them I was pretty heartset on installing MySQL 5.1, mainly because of its loadable plugin features where you can install a plugin or module without having to recompile the whole damn thing. Upgrading to 5.1 is easy, you just have to follow the right steps.

First, I would recommend upgrading to cPanel 11 or EDGE, which should have support for compiling Apache with non-supported versions of MySQL. On this server, I’m currently running 11 on the bleeding edge build. Also, it’s a splendid idea to dump all your databases before upgrading.
Note that these instructions mention MySQL 5.1.20-beta because that’s the latest release available at the time of my writing….but you can essentially follow this guide for any version of MySQL!

1. Copy the MySQL libraries from the server into a temporary location:

mkdir /root/sqllibs
cp /usr/lib/libmysqlclient.* /root/sqllibs

2. Find any installed MySQL packages:
rpm -qa | grep -i mysql-

This should present a list of installed rpm’s…remove them with rpm -e ,but note that some may need to be removed before others. Some people also would remove the /var/lib/mysql directory, but you can leave that there.

3. Download and install the MySQL 5.1.x packages:

Hop on over to http://dev.mysql.com/downloads/mysql/5.1.html#linux-x86-32bit-rpms and download the 5.1 RPM’s and install them:
rpm -i MySQL-client-5.1.20-0.glibc23.i386.rpm
rpm -i MySQL-devel-5.1.20-0.glibc23.i386.rpm
rpm -i MySQL-embedded-5.1.20-0.glibc23.i386.rpm
rpm -i MySQL-test-5.1.20-0.glibc23.i386.rpm
rpm -i MySQL-server-5.1.20-0.glibc23.i386.rpm

4. Prepare cPanel

You’ll want to make sure that cPanel’s updates don’t reset the MySQL version, so you need to run the following commands to force cPanel to skip MySQL updates:
touch /etc/mysqldisable
touch /etc/mysqlupdisable

Now edit /var/cpanel/cpanel.config and change the MySQL version to 5.1

Create the symlink:
ln -s /var/lib/mysql/mysql.sock /tmp

Also, verify that the MySQL version is correct by running mysql -V

root@vps [~]# mysql -V
mysql Ver 14.13 Distrib 5.1.20-beta, for pc-linux-gnu (i686) using readline 5.0

5. Set up MySQL

MySQL should have already been started at this point, so you can attempt to log in as root using mysql -u root . If you are able to log in on the first try, great. If not, you’ll need to reset the MySQL password:
pico /etc/my.cnf

Add this line, and restart MySQL
skip-grant-tables
service mysql restart

Now log into MySQL root and set the password:


mysql -u root
mysql> FLUSH PRIVILEGES;
mysql> GRANT ALL PRIVILEGES ON *.* TO root@localhost IDENTIFIED BY ‘yourpassword’ WITH GRANT OPTION;
mysql> FLUSH PRIVILEGES;
mysql> exit;

service mysql restart

When you’re done, remove the skip-grant-tables line from /etc/my.cnf and restart MySQL. Then log into Webhost Manager and reset the password *again*… this is necessary to build a bridge between the linux root user and the MySQL root user, so you can log into MySQL both through WHM’s phpMyAdmin, and SSH without a password when logged into the server as root.

All you need to do now is recompile Apache, but move the MySQL libraries back so easyapache can find them:

mv /root/sqllibs/libmysqlclient.* /usr/lib/mysql/

I haven’t tested too many configurations yet, but what works for me is Apache 2.2.4 with php 5.2.3, compiled with MySQL and mysqli, but NOT system MySQL.

Source : http://www.ducea.com/2006/07/16/cpanel-upgrading-to-mysql5/

CPanel has included support for MySQL 5 in all its latest releases - 10.8.2-xxx – (Stable/Release/Current). I find this very cool and it is a big difference in trying to get MySQL4 to run on Plesk for example. Anyway the upgrade process is very simple, and probably no one will need any additional information to complete this safely. I just wanted to point out some of the problems you might encounter in performing this upgrade.
How can you upgrade to MySQL5? Simply login to the WHM interface, and from “Server Configuration / Tweak Settings” choose in the “MySQL” section the 5.0 radio button. Then click “Save” and you are done. This will actually run the script: /scripts/mysqlup that will download and install the latest MySQL5 rpms available at that time.
After completion as instructed you should rebuild your perl mysql libraries and rebuild apache (to have php build against the newly installed mysql library).

/scripts/perlinstaller --force Bundle::DBD::mysql

and for apache/php:

/scripts/easyapache

or you can see this post for more details on compiling apache/php on CPanel from WHM.

What should you be aware prior to perform this upgrade? Here are some issues that you might find useful to know before doing this…

1. The upgrade is not reversible…

Even if you see the warning and this is even in bold:

“Updating from a previous verion of MySQL to a later version is not automaticlly reversable. You should backup your databases if you think you might wish to downgrade in the future.”

you might not believe it… Well I have not believed it as I have performed safely downgrades to mysql4.1 in case of problems on manual installs of mysql. But in this case CPanel is telling the truth… After you will complete the upgrade in WHM the choice for MySQL 4.1 (the radio button) will disappear and you will no longer be able to choose it. You can probably downgrade manually if you really need to, by downloading the MySQL4 rpms and install them manually from the command line while removing the MySQL5 ones. In this case you might find useful the link to the location of CPanel rpms:

http://updates.cpanel.net/pub/mysqlinstall/

2. MySQL might fail to start…

Since I have done this only on RHEL4 servers I am not aware if this problem exists on other distributions as well. But in RHEL the MySQL5 init script was failing after the upgrade with the following error:

/etc/init.d/mysql start
Starting MySQLCouldn't find MySQL manager or server        [FAILED]

Tracking down this error I found out that the MySQL configuration file (/etc/my.cnf) installed by the upgrade had a wrong line that was causing this behaviour:

/etc/my.cnf
[mysqld]
datadir=/var/lib/mysql
socket=/var/lib/mysql/mysql.sock
# Default to using old password format for compatibility with mysql 3.x
# clients (those using the mysqlclient10 compatibility package).
#old_passwords=1

[mysql.server]
user=mysql
basedir=/var/lib    # <= you will need to comment this line
old-passwords = 1

[mysqld_safe]
err-log=/var/log/mysqld.log
pid-file=/var/run/mysqld/mysqld.pid

The line basedir=/var/lib was causing the error and in case you are having the same problem commenting out that line will solve the problem and MySQL will start properly.

These are the 2 issues I have found out when upgrading MySQL5 and hopefully you will be aware of them prior to loosing too much time trying to solve them Besides this MySQL5 is running fine and I have not found any problems in normal operation or with the integration with other CPanel functions. Have fun.

Source: http://searchenterpriselinux.techtarget.com/tip/0,289483,sid39_gci1130131,00.html

If a company is running MySQL 4 now and is happy with it, shouldn’t it stick with that version? Yes and no, says Mike Hillyer, this site’s resident MySQL expert. In this tip, he discusses when and why MySQL users should upgrade, the benefits of MySQL’s new features, and how to evaluate and deploy the upcoming MySQL 5.0, now available in its beta release.

Many companies keep a policy of staying one version back from the latest release, meaning that they use Windows 2000 instead of Windows XP, MySQL 4 instead of 4.1, and so on. Such a policy promotes stability over features.

So, companies that find MySQL 4 sufficient for their needs may want to stay where they are because MySQL 4 and MySQL 4.1 are quite stable at the moment and work reliably.

Why would that company want to move to MySQL 5 now? The biggest three features of interest to most companies are stored procedures, triggers, and views.

MySQL 5′s big bonuses

Stored procedures allow you to move business logic from end applications to the MySQL server, which can save effort when you have multiple end applications (instead of implementing a price calculation routine in PHP for the web and VC for the desktop, you can implement it in a stored procedure and call it from both PHP and VC).

Stored procedures can also enhance security by allowing you to prevent a user from accessing a table directly, but instead giving them permission to call a stored procedure that has access to the table.

Triggers are stored routines that are written with a syntax like that of stored procedures, but instead of being called by a user or application, triggers are activated by table events such as inserts, updates, and deletes. The triggers can modify or abort the triggering table actions, or take the information provided by the action and use it elsewhere.

I recently used a trigger to create a MyISAM FULLTEXT lookup table for an InnoDB table: any inserts, updates, or deletes to the InnoDB table were mirrored to the lookup table by triggers, and the end users didn’t have to change anything about the way they interacted with the InnoDB table.

Views are essentially named virtual tables defined by SQL queries. I can take a complex set of tables, create a SELECT query that might be more meaningful to end users, then turn it into a view. The end users can then perform SELECT queries against the view and, in most cases, also execute INSERT, UPDATE, and DELETE statements against the view, with the changes being reflected in the underlying tables. Views help to simplify complicated data and also enhance security. As with a stored procedure, you can create a view and give a user permission to SELECT from the view but not the underlying table.

Evaluating MySQL 5

In the end most users will eventually move to MySQL 5 as MySQL 4 and 4.1 age and become outdated. The timing will have to depend on whether you consider the features of MySQL 5 to be useful to your organization.

When evaluating the new features, I would recommend installing MySQL 5 on a separate machine and trying it with your existing applications, run as many tests as you can and see if everything runs smoothly. If you do not encounter any errors you can then bring MySQL 5 into your production systems (after a production release of MySQL 5).

There really should not be things to watch out for, in the sense of bugs or incompatibilities, but you can always watch the changelogs at the 5.0 news page on MySQL’s site and look for entries that are marked ‘Incompatible Change’.

So far, bug reports have been many and varied, depending on the feature being used. As expected, most of the bugs are related to new MySQL features, such as stored procedures, triggers, and views. The full list of features added and bugs fixed can be browsed in MySQL’s 5.0 news.

Preparing for an upgrade

The best tip before upgrading is to back up your data: while the upgrade process should be relatively painless, not having a backup is a recipe for disaster.

Those looking to upgrade major versions of MySQL in a production environment should test and evaluate their systems before upgrading. The ideal would be to install all software on a test machine, upgrade the MySQL installation on the test machine to MySQL 5, and then run the test machine with real data for a while to ensure there are no suprises. If all goes well on the test machine you can then move the production systems to the newer version.

Production machines should also only be upgraded to a production version of MySQL. While the beta versions of MySQL have been very stable, there are no guarantees that your application will run flawlessly on beta software.

A common error when upgrading from MySQL 4.0 to MySQL 4.1 is password hashing. Users who encounter an error such as "Client does not support authentication protocol requested" can find at solution at OpenWin.org.

There are detailed upgrade notes for all versions of MySQL on this MySQL.com page.

Most applications should not have any problem with MySQL 5, as opposed to MySQL 4.1. However, users upgrading from MySQL 4.0 should first upgrade to MySQL 4.1, then upgrade to MySQL 5. You can get all MySQL downloads on MySQL’s download page.

Source: http://dev.mysql.com/doc/refman/5.0/en/upgrading-from-4-1.html

Note

It is good practice to back up your data before installing any new version of software. Although MySQL works very hard to ensure a high level of quality, you should protect your data by making a backup. MySQL recommends that you dump and reload your tables from any previous version to upgrade to 5.0.

In general, you should do the following when upgrading from MySQL 4.1 to 5.0:

• Read all the items in the following sections to see whether any of them might affect your applications:
  • Section 2.18, “Upgrading MySQL”, has general update information.
  • The items in the change lists found later in this section enable you to identify upgrade issues that apply to your current MySQL installation.
  • The MySQL 5.0 change history describes significant new features you can use in 5.0 or that differ from those found in MySQL 4.1. Some of these changes may result in incompatibilities. See Section E.1, “Changes in release 5.0.x (Production)”.
• Note particularly any changes that are marked Known issue or Incompatible change. These incompatibilities with earlier versions of MySQL may require your attention before you upgrade.

Our aim is to avoid these changes, but occasionally they are necessary to correct problems that would be worse than an incompatibility between releases. If any upgrade issue applicable to your installation involves an incompatibility that requires special handling, follow the instructions given in the incompatibility description. Often this will involve a dump and reload, or use of a statement such as CHECK TABLE or REPAIR TABLE.

A dump and reload is done like this:

• Dump the affected tables with mysqldump before upgrading
• Reload the dump file (for example, with mysql) to recreate the tables after upgrading

Any procedure that involves REPAIR TABLE with the USE_FRM option must be done before upgrading. Use of this statement with a version of MySQL different from the one used to create the table (that is, using it after upgrading) may damage the table. See Section 12.5.2.6, “REPAIR TABLE Syntax”.

• After you upgrade to a new version of MySQL, run mysql_upgrade (see Section 4.4.9, “mysql_upgrade — Check Tables for MySQL Upgrade”). This program will check your tables, and repair them if necessary. It will also update your grant tables to make sure that they have the current structure so that you can take advantage of any new capabilities. (Some releases of MySQL introduce changes to the structure of the grant tables to add new privileges or features.)
• If you are running MySQL Server on Windows, see Section 2.9.14, “Upgrading MySQL on Windows”.
• MySQL 5.0 adds support for stored procedures. This support requires the mysql.proc table. To create this table, you should run the mysql_upgrade program as described in Section 4.4.9, “mysql_upgrade — Check Tables for MySQL Upgrade”.
• MySQL 5.0 adds support for views. This support requires extra privilege columns in the mysql.user and mysql.db tables. To create these columns, you should run the mysql_upgrade program as described in Section 4.4.9, “mysql_upgrade — Check Tables for MySQL Upgrade”.
• If you are using replication, see Section 16.3.3, “Upgrading a Replication Setup”, for information on upgrading your replication setup.

Several visible behaviors have changed between MySQL 4.1 and MySQL 5.0 to make MySQL more compatible with standard SQL. These changes may affect your applications.

The following lists describe changes that may affect applications and that you should watch out for when upgrading to MySQL 5.0.

Server Changes:

• Incompatible change: The indexing order for end-space in TEXT columns for InnoDB and MyISAM tables has changed. Starting from 5.0.3, TEXT indexes are compared as space-padded at the end (just as MySQL sorts CHAR, VARCHAR and TEXT fields). If you have a index on a TEXT column, you should run CHECK TABLE on it. If the check reports errors, rebuild the indexes: Dump and reload the table if it is an InnoDB table, or run OPTIMIZE TABLE or REPAIR TABLE if it is a MyISAM table.
• Incompatible change. For BINARY columns, the pad value and how it is handled has changed as of MySQL 5.0.15. The pad value for inserts now is 0×00 rather than space, and there is no stripping of the pad value for retrievals. For details, see Section 10.4.2, “The BINARY and VARBINARY Types”.
• Incompatible change: As of MySQL 5.0.3, the server by default no longer loads user-defined functions (UDFs) unless they have at least one auxiliary symbol (for example, an xxx_init or xxx_deinit symbol) defined in addition to the main function symbol. This behavior can be overridden with the –allow-suspicious-udfs option. See Section 21.2.2.6, “User-Defined Function Security Precautions”.
• Incompatible change: As of MySQL 5.0.13, InnoDB rolls back only the last statement on a transaction timeout. In MySQL 5.0.32, a new option, –innodb_rollback_on_timeout, causes InnoDB to abort and roll back the entire transaction if a transaction timeout occurs (the same behavior as in MySQL 4.1).
• Incompatible change: For ENUM columns that had enumeration values containing commas, the commas were mapped to 0xff internally. However, this rendered the commas indistinguishable from true 0xff characters in the values. This no longer occurs. However, the fix requires that you dump and reload any tables that have ENUM columns containing true 0xff in their values: Dump the tables using mysqldump with the current server before upgrading from a version of MySQL 5.0 older than 5.0.36 to version 5.0.36 or newer.
• Incompatible change: The update log has been removed in MySQL 5.0. If you had enabled it previously, you should enable the binary log instead.
• Incompatible change: Support for the ISAM storage engine has been removed in MySQL 5.0. If you have any ISAM tables, you should convert them before upgrading. For example, to convert an ISAM table to use the MyISAM storage engine, use this statement:

· ALTER TABLE tbl_name ENGINE = MyISAM;

Use a similar statement for every ISAM table in each of your databases.

• Incompatible change: Support for RAID options in MyISAM tables has been removed in MySQL 5.0. If you have tables that use these options, you should convert them before upgrading. One way to do this is to dump them with mysqldump, edit the dump file to remove the RAID options in the CREATE TABLE statements, and reload the dump file. Another possibility is to use CREATE TABLE new_tbl … SELECT raid_tbl to create a new table from the RAID table. However, the CREATE TABLE part of the statement must contain sufficient information to re-create column attributes as well as indexes, or column attributes may be lost and indexes will not appear in the new table. See Section 12.1.10, “CREATE TABLE Syntax”.

The .MYD files for RAID tables in a given database are stored under the database directory in subdirectories that have names consisting of two hex digits in the range from 00 to ff. After converting all tables that use RAID options, these RAID-related subdirectories still will exist but can be removed. Verify that they are empty, and then remove them manually. (If they are not empty, there is some RAID table that has not been converted.)

• Incompatible change: Beginning with MySQL 5.0.42, when a DATE value is compared with a DATETIME value, the DATE value is coerced to the DATETIME type by adding the time portion as 00:00:00. Previously, the time portion of the DATETIME value was ignored, or the comparison could be performed as a string comparison. To mimic the old behavior, use the CAST() function as shonw in this example: SELECT date_col = CAST(NOW() AS DATE) FROM table;.
• As of MySQL 5.0.25, the lc_time_names system variable specifies the locale that controls the language used to display day and month names and abbreviations. This variable affects the output from the DATE_FORMAT(), DAYNAME() and MONTHNAME() functions. See Section 9.8, “MySQL Server Locale Support”.
• In MySQL 5.0.6, binary logging of stored routines and triggers was changed. This change has implications for security, replication, and data recovery, as discussed in Section 18.5, “Binary Logging of Stored Programs”.
• As of MySQL 5.0.28, mysqld_safe no longer implicitly invokes mysqld-max if it exists. Instead, it invokes mysqld unless a –mysqld or –mysqld-version option is given to specify another server explicitly. If you previously relied on the implicit invocation of mysqld-max, you should use an appropriate option now.

SQL Changes:

• Important note: Prior to MySQL 5.0.46, the parser accepted invalid code in SQL condition handlers, leading to server crashes or unexpected execution behavior in stored programs. Specifically, the parser allowed a condition handler to refer to labels for blocks that enclose the handler declaration. This was incorrect because block label scope does not include the code for handlers declared within the labeled block.

As of 5.0.46, the parser rejects this invalid construct, but if you upgrade in place (without dumping and reloading your databases), existing handlers that contain the construct still are invalid even if they appear to function as you expect and should be rewritten.

To find affected handlers, use mysqldump to dump all stored functions and procedures, triggers, and events. Then attempt to reload them into an upgraded server. Handlers that contain illegal label references will be rejected.

For more information about condition handlers and writing them to avoid invalid jumps, see Section 12.8.4.2, “DECLARE for Handlers”.

• Incompatible change: If you have created a user-defined function (UDF) with a given name and upgrade MySQL to a version that implements a new built-in function with the same name, the UDF becomes inaccessible. To correct this, use DROP FUNCTION to drop the UDF, and then use CREATE FUNCTION to re-create the UDF with a different non-conflicting name. If a new version of MySQL implements a built-in function with the same name as an existing stored function, you have two choices: Rename the stored function to use a non-conflicting name, or change calls to the function so that they use a database qualifier (that is, use db_name.func_name() syntax). See Section 8.2.3, “Function Name Parsing and Resolution”, for the rules describing how the server interprets references to different kinds of functions.
• Incompatible change: The parser accepted statements that contained /* … */ that were not properly closed with */, such as SELECT 1 /* + 2. As of MySQL 5.0.50, statements that contain unclosed /*-comments now are rejected with a syntax error.

This fix has the potential to cause incompatibilities. Because of Bug#26302, which caused the trailing */ to be truncated from comments in views, stored routines, triggers, and events, it is possible that objects of those types may have been stored with definitions that now will be rejected as syntactically invalid. Such objects should be dropped and re-created so that their definitions do not contain truncated comments. If a stored object definition contains only a single statement (does not use a BEGIN … END block) and contains a comment within the statement, the comment should be moved to follow the statement or the object should be rewritten to use a BEGIN … END block. For example, this statement:

CREATE PROCEDURE p() SELECT 1 /* my comment */ ;

Can be rewritten in either of these ways:

CREATE PROCEDURE p() SELECT 1; /* my comment */

CREATE PROCEDURE p() BEGIN SELECT 1 /* my comment */ ; END;

• Incompatible change: Beginning with MySQL 5.0.12, natural joins and joins with USING, including outer join variants, are processed according to the SQL:2003 standard. The changes include elimination of redundant output columns for NATURAL joins and joins specified with a USING clause and proper ordering of output columns. The precedence of the comma operator also now is lower compared to JOIN, LEFT JOIN, and so forth.

These changes make MySQL more compliant with standard SQL. However, they can result in different output columns for some joins. Also, some queries that appeared to work correctly prior to 5.0.12 must be rewritten to comply with the standard. For details about the scope of the changes and examples that show what query rewrites are necessary, see Section 12.2.8.1, “JOIN Syntax”.

• Incompatible change: The namespace for triggers has changed in MySQL 5.0.10. Previously, trigger names had to be unique per table. Now they must be unique within the schema (database). An implication of this change is that DROP TRIGGER syntax now uses a schema name instead of a table name (schema name is optional and, if omitted, the current schema will be used).

After upgrading from a previous version of MySQL 5 to MySQL 5.0.10 or newer, you must drop all triggers and re-create them or DROP TRIGGER will not work after the upgrade. Here is a suggested procedure for doing this:

1. Upgrade to MySQL 5.0.10 or later to be able to access trigger information in the INFORMATION_SCHEMA.TRIGGERS table. (It should work even for pre-5.0.10 triggers.)
2. Dump all trigger definitions using the following SELECT statement:

3. SELECT CONCAT(‘CREATE TRIGGER ‘, t.TRIGGER_SCHEMA, ‘.’, t.TRIGGER_NAME,

4. ‘ ‘, t.ACTION_TIMING, ‘ ‘, t.EVENT_MANIPULATION, ‘ ON ‘,

5. t.EVENT_OBJECT_SCHEMA, ‘.’, t.EVENT_OBJECT_TABLE,

6. ‘ FOR EACH ROW ‘, t.ACTION_STATEMENT, ‘//’ )

7. INTO OUTFILE ‘/tmp/triggers.sql’

8. FROM INFORMATION_SCHEMA.TRIGGERS AS t;

The statement uses INTO OUTFILE, so you must have the FILE privilege. The file will be created on the server host. Use a different filename if you like. To be 100% safe, inspect the trigger definitions in the triggers.sql file, and perhaps make a backup of the file.

1. Stop the server and drop all triggers by removing all .TRG files in your database directories. Change location to your data directory and issue this command:

10.shell> rm */*.TRG

1. Start the server and re-create all triggers using the triggers.sql file. For the file created earlier, use these commands in the mysql program:

12.mysql> delimiter // ;

13.mysql> source /tmp/triggers.sql //

1. Use the SHOW TRIGGERS statement to check that all triggers were created successfully.
• Incompatible change: As of MySQL 5.0.15, the CHAR() function returns a binary string rather than a string in the connection character set. An optional USING charset_name clause may be used to produce a result in a specific character set instead. Also, arguments larger than 256 produce multiple characters. They are no longer interpreted modulo 256 to produce a single character each. These changes may cause some incompatibilities:

• CHAR(ORD(‘A’)) = ‘a’ is no longer true:

o mysql> SELECT CHAR(ORD(‘A’)) = ‘a’;

o +———————-+

o | CHAR(ORD(‘A’)) = ‘a’ |

o +———————-+

o | 0 |

o +———————-+

To perform a case-insensitive comparison, you can produce a result string in a non-binary character set by adding a USING clause or converting the result:

mysql> SELECT CHAR(ORD(‘A’) USING latin1) = ‘a’;

+———————————–+

| CHAR(ORD(‘A’) USING latin1) = ‘a’ |

+———————————–+

| 1 |

+———————————–+

mysql> SELECT CONVERT(CHAR(ORD(‘A’)) USING latin1) = ‘a’;

+——————————————–+

| CONVERT(CHAR(ORD(‘A’)) USING latin1) = ‘a’ |

+——————————————–+

| 1 |

+——————————————–+

• CREATE TABLE … SELECT CHAR(…) produces a VARBINARY column, not a VARCHAR column. To produce a VARCHAR column, use USING or CONVERT() as just described to convert the CHAR() result into a non-binary character set.
• Previously, the following statements inserted the value 0×00410041 (‘AA’ as a ucs2 string) into the table:

o CREATE TABLE t (ucs2_column CHAR(2) CHARACTER SET ucs2);

o INSERT INTO t VALUES (CHAR(0×41,0×41));

As of MySQL 5.0.15, the statements insert a single ucs2 character with value 0×4141.

• Incompatible change: By default, integer subtraction involving an unsigned value should produce an unsigned result. Tracking of the “unsignedness” of an expression was improved in MySQL 5.0.13. This means that, in some cases where an unsigned subtraction would have resulted in a signed integer, it now results in an unsigned integer. One context in which this difference manifests itself is when a subtraction involving an unsigned operand would be negative.

Suppose that i is a TINYINT UNSIGNED column and has a value of 0. The server evaluates the following expression using 64-bit unsigned integer arithmetic with the following result:

mysql> SELECT i – 1 FROM t;

+———————-+

| i – 1 |

+———————-+

| 18446744073709551615 |

+———————-+

If the expression is used in an UPDATE t SET i = i – 1 statement, the expression is evaluated and the result assigned to i according to the usual rules for handling values outside the column range or 0 to 255. That is, the value is clipped to the nearest endpoint of the range. However, the result is version-specific:

• Before MySQL 5.0.13, the expression is evaluated but is treated as the equivalent 64-bit signed value (–1) for the assignment. The value of –1 is clipped to the nearest endpoint of the column range, resulting in a value of 0:

o mysql> UPDATE t SET i = i – 1; SELECT i FROM t;

o +——+

o | i |

o +——+

o | 0 |

o +——+

• As of MySQL 5.0.13, the expression is evaluated and retains its unsigned attribute for the assignment. The value of 18446744073709551615 is clipped to the nearest endpoint of the column range, resulting in a value of 255:

o mysql> UPDATE t SET i = i – 1; SELECT i FROM t;

o +——+

o | i |

o +——+

o | 255 |

o +——+

To get the older behavior, use CAST() to convert the expression result to a signed value:

UPDATE t SET i = CAST(i – 1 AS SIGNED);

Alternatively, set the NO_UNSIGNED_SUBTRACTION SQL mode. However, this will affect all integer subtractions involving unsigned values.

• Incompatible change: Before MySQL 5.0.13, NOW() and SYSDATE() return the same value (the time at which the statement in which the function occurs begins executing). As of MySQL 5.0.13, SYSDATE() returns the time at which it executes, which can differ from the value returned by NOW(). For information about the implications for binary logging, replication, and use of indexes, see the description for SYSDATE() in Section 11.6, “Date and Time Functions” and for SET TIMESTAMP in Section 12.5.4, “SET Syntax”. To restore the former behavior for SYSDATE() and cause it to be an alias for NOW(), start the server with the –sysdate-is-now option (available as of MySQL 5.0.20).
• Incompatible change: Before MySQL 5.0.13, GREATEST(x,NULL) and LEAST(x,NULL) return x when x is a non-NULL value. As of 5.0.3, both functions return NULL if any argument is NULL, the same as Oracle. This change can cause problems for applications that rely on the old behavior.
• Incompatible change: Before MySQL 4.1.13/5.0.8, conversion of DATETIME values to numeric form by adding zero produced a result in YYYYMMDDHHMMSS format. The result of DATETIME+0 is now in YYYYMMDDHHMMSS.000000 format.
• Incompatible change: In MySQL 4.1.12/5.0.6, the behavior of LOAD DATA INFILE and SELECT … INTO OUTFILE has changed when the FIELDS TERMINATED BY and FIELDS ENCLOSED BY values both are empty. Formerly, a column was read or written the display width of the column. For example, INT(4) was read or written using a field with a width of 4. Now columns are read and written using a field width wide enough to hold all values in the field. However, data files written before this change was made might not be reloaded correctly with LOAD DATA INFILE for MySQL 4.1.12/5.0.6 and up. This change also affects data files read by mysqlimport and written by mysqldump –tab, which use LOAD DATA INFILE and SELECT … INTO OUTFILE. For more information, see Section 12.2.6, “LOAD DATA INFILE Syntax”.
• Incompatible change: The implementation of DECIMAL has changed in MySQL 5.0.3. You should make your applications aware of this change. For information about this change, and about possible incompatibilities with old applications, see Section 11.13, “Precision Math”, in particular, Section 11.13.2, “DECIMAL Data Type Changes”.

DECIMAL columns are stored in a more efficient format. To convert a table to use the new DECIMAL type, you should do an ALTER TABLE on it. (The ALTER TABLE also will change the table’s VARCHAR columns to use the new VARCHAR data type properties, described in a separate item.)

A consequence of the change in handling of the DECIMAL and NUMERIC fixed-point data types is that the server is more strict to follow standard SQL. For example, a data type of DECIMAL(3,1) stores a maximum value of 99.9. Before MySQL 5.0.3, the server allowed larger numbers to be stored. That is, it stored a value such as 100.0 as 100.0. As of MySQL 5.0.3, the server clips 100.0 to the maximum allowable value of 99.9. If you have tables that were created before MySQL 5.0.3 and that contain floating-point data not strictly legal for the data type, you should alter the data types of those columns. For example:

ALTER TABLE tbl_name MODIFY col_name DECIMAL(4,1);

The behavior used by the server for DECIMAL columns in a table depends on the version of MySQL used to create the table. If your server is from MySQL 5.0.3 or higher, but you have DECIMAL columns in tables that were created before 5.0.3, the old behavior still applies to those columns. To convert the tables to the newer DECIMAL format, dump them with mysqldump and reload them.

• Incompatible change: MySQL 5.0.3 and up uses precision math when calculating with DECIMAL and integer columns (64 decimal digits) and for rounding exact-value numbers. Rounding behavior is well-defined, not dependent on the implementation of the underlying C library. However, this might result in incompatibilities for applications that rely on the old behavior. (For example, inserting .5 into an INT column results in 1 as of MySQL 5.0.3, but might be 0 in older versions.) For more information about rounding behavior, see Section 11.13.4, “Rounding Behavior”, and Section 11.13.5, “Precision Math Examples”.
• Incompatible change: MyISAM and InnoDB tables created with DECIMAL columns in MySQL 5.0.3 to 5.0.5 will appear corrupt after an upgrade to MySQL 5.0.6. (The same incompatibility will occur for these tables created in MySQL 5.0.6 after a downgrade to MySQL 5.0.3 to 5.0.5.) If you have such tables, check and repair them with mysql_upgrade after upgrading. See Section 4.4.9, “mysql_upgrade — Check Tables for MySQL Upgrade”.
• Incompatible change: For user-defined functions, exact-value decimal arguments such as 1.3 or DECIMAL column values were passed as REAL_RESULT values prior to MySQL 5.0.3. As of 5.0.3, they are passed as strings with a type of DECIMAL_RESULT. If you upgrade to 5.0.3 and find that your UDF now receives string values, use the initialization function to coerce the arguments to numbers as described in Section 21.2.2.3, “UDF Argument Processing”.
• Incompatible change: Before MySQL 5.0.2, SHOW STATUS returned global status values. The default as of 5.0.2 is to return session values, which is incompatible with previous versions. To issue a SHOW STATUS statement that will retrieve global status values for all versions of MySQL, write it like this:

· SHOW /*!50002 GLOBAL */ STATUS;

• Incompatible change: User variables are not case sensitive in MySQL 5.0. In MySQL 4.1, SET @x = 0; SET @X = 1; SELECT @x; created two variables and returned 0. In MySQL 5.0, it creates one variable and returns 1. Replication setups that rely on the old behavior may be affected by this change.
• Some keywords are reserved in MySQL 5.0 that were not reserved in MySQL 4.1. See Section 8.3, “Reserved Words”.
• The LOAD DATA FROM MASTER and LOAD TABLE FROM MASTER statements are deprecated. See Section 12.6.2.2, “LOAD DATA FROM MASTER Syntax”, for recommended alternatives.
• As of MySQL 5.0.3, trailing spaces no longer are removed from values stored in VARCHAR and VARBINARY columns. The maximum lengths for VARCHAR and VARBINARY columns in MySQL 5.0.3 and later are 65,535 characters and 65,535 bytes, respectively.

When a binary upgrade (filesystem-level copy of data files) to MySQL 5.0 is performed for a table with a VARBINARY column, the column is space-padded to the full allowable width of the column. This causes values in VARBINARY columns that do not occupy the full width of the column to include extra trailing spaces after the upgrade, which means that the data in the column is different.

In addition, new rows inserted into a table upgraded in this way will be space padded to the full width of the column.

This issue can be resolved as follows:

1. For each table containing VARBINARY columns, execute the statement

1. ALTER TABLE table_name ENGINE=engine_name;

where table_name is the name of the table and engine_name is the name of the storage engine currently used by table_name. In other words, if the table named mytable uses the MyISAM storage engine, then you would use this statement:

ALTER TABLE mytable ENGINE=MYISAM;

This rebuilds the table so that it uses the 5.0 VARBINARY format.

1. Then you must remove all trailing spaces from any VARBINARY column values. For each VARBINARY column varbinary_column, you should perform the following statement (where table_name is the name of the table containing the VARBINARY column):

3. UPDATE table_name SET varbinary_column = RTRIM(varbinary_column);

This is necessary and safe because trailing spaces are stripped before 5.0.3, meaning that any trailing spaces are erroneous.

This problem does not occur (and thus these two steps are not required) for tables upgraded using the recommended procedure of dumping tables prior to the upgrade and reloading them afterwards.

Note

If you create a table with new VARCHAR or VARBINARY columns in MySQL 5.0.3 or later, the table will not be usable if you downgrade to a version older than 5.0.3. Dump the table with mysqldump before downgrading and reload it after downgrading.

• Comparisons made between FLOAT or DOUBLE values that happened to work in MySQL 4.1 may not do so in 5.0. Values of these types are imprecise in all MySQL versions, and you are strongly advised to avoid such comparisons as WHERE col_name=some_double, regardless of the MySQL version you are using. See Section B.1.5.8, “Problems with Floating-Point Comparisons”.
• As of MySQL 5.0.3, BIT is a separate data type, not a synonym for TINYINT(1). See Section 10.1.1, “Overview of Numeric Types”.
• MySQL 5.0.2 adds several SQL modes that allow stricter control over rejecting records that have invalid or missing values. See Section 5.1.7, “Server SQL Modes”, and Section 1.7.6.2, “Constraints on Invalid Data”. If you want to enable this control but continue to use MySQL’s capability for storing incorrect dates such as ’2004-02-31′, you should start the server with –sql_mode="TRADITIONAL,ALLOW_INVALID_DATES".
• As of MySQL 5.0.2, the SCHEMA and SCHEMAS keywords are accepted as synonyms for DATABASE and DATABASES, respectively. (While “schemata” is grammatically correct and even appears in some MySQL 5.0 system database and table names, it cannot be used as a keyword.)
• As of MySQL 5.0.25, TIMESTAMP columns that are NOT NULL now are reported that way by SHOW COLUMNS and INFORMATION_SCHEMA, rather than as NULL.

C API Changes:

• Incompatible change: Because the MySQL 5.0 server has a new implementation of the DECIMAL data type, a problem may occur if the server is used by older clients that still are linked against MySQL 4.1 client libraries. If a client uses the binary client/server protocol to execute prepared statements that generate result sets containing numeric values, an error will be raised: ‘Using unsupported buffer type: 246′

This error occurs because the 4.1 client libraries do not support the new MYSQL_TYPE_NEWDECIMAL type value added in 5.0. There is no way to disable the new DECIMAL data type on the server side. You can avoid the problem by relinking the application with the client libraries from MySQL 5.0.

• Incompatible change: The ER_WARN_DATA_TRUNCATED warning symbol was renamed to WARN_DATA_TRUNCATED in MySQL 5.0.3.
• The reconnect flag in the MYSQL structure is set to 0 by mysql_real_connect(). Only those client programs which did not explicitly set this flag to 0 or 1 after mysql_real_connect() experience a change. Having automatic reconnection enabled by default was considered too dangerous (due to the fact that table locks, temporary tables, user variables, and session variables are lost after reconnection).

MySQL Enterprise. MySQL Enterprise subscribers will find more information about upgrading in the Knowledge Base articles found at Upgrading. Access to the MySQL Knowledge Base collection of articles is one of the advantages of subscribing to MySQL Enterprise. For more information, see http://www.mysql.com/products/enterprise/advisors.html.