DRBD is a high-availability solution for MySQL that combines MySQL, Linux Heartbeat and Distributed Replicated Block Device (DRBD) for a hot-standby solution that synchronously replicates MySQL data between the primary and secondary server.

The key benefit of DRBD over replication is that it enforces data synchronization between the primary and secondary machine, ensuring that the secondary machine has the exact same data as the primary at the time of failover. Replication depends on log shipping and has no guarantee of data synchronization.

DRBD is fully supported by MySQL AB for their enterprise customers.

Further Reference

MySQL and DRBD High Availability Architectures (Whitepaper, Registration required)

DRBD FAQ (MySQL Reference Manual)

An Introduction to High Availability Architectures with MySQL and DRBD (Webinar)

A Quick Tour of DRBD

Error 1045 is returned when a user is denied permission to connect to the MySQL server.

Sample

[localhost]$ mysql
ERROR 1045 (28000): Access denied for user ‘root’@'localhost’ (using password: NO)

Resolution

• If the message ends with ‘(using password: NO)’, no password was specified while connecting. Add -p to the call to the mysql client:
  

  mysql -p

• If the username in the error message is not the one you need to use to connect to MySQL, specify the desired username with the -u flag:
  

  mysql -u mike -p

  When -u is omitted, the mysql client uses the logged-in username on the OS (root in the example above).

• Authentication is based on a combination of user and the host being connected from (’root’ connecting from ‘localhost’ in the example above). Check that the connecting host listed is the one you have permission to connect from.
• If you are connecting from the correct host using the correct username, it means that you are providing the wrong password or the user does not exist. See the Adding Users link in the following section.

Further Reference

Causes of Access Denied Errors (MySQL Reference Manual)

Connecting to the MySQL Server (MySQL Reference Manual)

Adding New User Accounts to MySQL (MySQL Reference Manual)

The SQL_CALC_FOUND_ROWS keyword is used when the result set of a query will be restricted by a LIMIT clause, instructing the MySQL server to store the number of rows that would have been returned had the result set not been restricted. The stored value is exposed through the FOUND_ROWS() function.

Sample

In this example, we first produce a list of users, restricted with the LIMIT clause, then we retrieve the full count of users with the FOUND_ROWS() function:

mysql> SELECT SQL_CALC_FOUND_ROWS emailaddress FROM users LIMIT 10,3;
+-----------------------------+
| emailaddress                |
+-----------------------------+
|  ben.@foo.com               |
|  charlie@bar.com            |
|  aaron@baz.com              |
+-----------------------------+
5 rows in set (0.00 sec)mysql>

SELECT FOUND_ROWS();
+--------------+
| FOUND_ROWS() |
+--------------+
|       435136 |
+--------------+
1 row in set (0.00 sec)

Further Reference

SELECT Syntax - MySQL Reference Manual

Found_Rows() - MySQL Reference Manual

Google Cache of Article on Improving COUNT(*) Performance

Proven Scaling is a MySQL consulting company founded by Jeremy Cole and Eric Bergen. Jeremy and Eric both formerly worked at Yahoo! and Jeremy was previously over training at MySQL AB.

Proven Scaling provides a variety of services from performance consulting to training and is located in the United States.

Further Reference

Proven Scaling

Jeremy Cole’s blog

Eric Bergen’s blog

Paul DuBois is a Senior Technical Writer working for MySQL AB.

Paul is the author of several books related to MySQL:

• MySQL (3rd Edition) (Developer’s Library)
• MySQL Cookbook
• MySQL 5.0 Certification Study Guide (MySQL Press)
• MySQL and Perl for the Web (Landmark)

Paul has also authored technical books unrelated to MySQL:

• Using csh & tcsh (Nutshell Handbooks)
• Software Portability with imake (Practical Software Engineering)

Paul was a speaker at the 2003 MySQL Users Conference & Expo on the subject of Using MySQL With Ruby.

Further Reference

KiteBird.com - Contains sample book chapters, presentation materials, articles by Paul Dubois

Session entry in 2003 Users Conference Site

Home Page for Paul DuBois

Amazon List of Books by Paul DuBois

Error 1033 generally points to corruption of the .frm file for the table being queried. This can be caused by InnoDB reconfiguration, form file corruption, and permissions issued.

Sample

SELECT COUNT(*) FROM auth;
ERROR 1033 (HY000): Incorrect information in file: './auth/auth.frm

Resolution

• Check that the permissions on /tmp/ allow for reading and writing by the mysql user.
• Stop MySQL, delete the ib_logfile0 and ib_logfile1 files from your MySQL datadir and start MySQL.
• Restore from a backup.

Further Reference

Explanation of Error 1033 in relation to InnoDB

Explanation of Error 1033 and /tmp/

Error 17 indicates that that either the MySQL server encountered an issue while trying to delete the directory containing the database to be dropped, or tried to create a temporary file that already existed during an ALTER TABLE statement.

Sample

mysql> DROP DATABASE foo;
Error dropping database (can’t rmdir ‘./foo/’, errno: 17)

mysql> ALTER TABLE foo …
Error on rename of ‘./bar/foo.frm’ to ‘./bar/B-foo.frm’ (Errcode: 17)

Resolution

• Check that the user the MySQL server is running under has permission to delete the directory.
• Check that there are no files in the directory that are not created by the MySQL server.
• Browse to the MySQL data directory and delete all files whose names start with A- or B-.
• Shut down MySQL, manually delete the directory listed.
• Use the latest version of MySQL.
• Use the mysqld-nt binaries when using Windows NT-based hosts.

Further Reference

Bug report related to Error 17 on bugs.mysql.com

perror - Explain Error Codes (MySQL Reference Manual)

Problems with ALTER TABLE (MySQL Reference Manual) 

The WITH ROLLUP clause is used with GROUP BY queries to generate extra rows in the dataset that represent group totals. Summary rows will show NULL in the group column(s) being summarized. WITH ROLLUP will summarize multiple level of groupings, providing totals across each group level. The WITH ROLLUP clause was added in MySQL 4.1.1.

The WITH ROLLUP clause cannot be used in a query with an ORDER BY clause. Summary columns can be manipulated in the query, allowing for functions like IFNULL() to be used to rename values in summary rows.

Sample

In this example, a query is performed to count customers in each city of each country, with summaries on a per-country and global basis. The per-country summary is identified by the presence of a NULL value in the city field, while the global summary is identified by the presence of a NULL value in both the city and country fields.

mysql> SELECT country.country, city.city, COUNT(address_id)
-> FROM country LEFT JOIN city USING (country_id)
-> LEFT JOIN address USING (city_id)
-> GROUP by country, city
-> WITH ROLLUP;

| Yugoslavia                            | Kragujevac                 |      1 |
| Yugoslavia                            | Novi Sad                   |      1 |
| Yugoslavia                            | NULL                       |      2 |
| Zambia                                | Kitwe                      |      1 |
| Zambia                                | NULL                       |      1 |
| NULL                                  | NULL                       |    603 |
+---------------------------------------+----------------------------+--------+
710 rows in set (0.00 sec)

Further Reference

GROUP BY Modifiers (MySQL Reference Manual)

Summarizing Data with ROLLUP

Summarizing Data with CUBE and ROLLUP

When the MySQL server is installed as a service on Windows, it tries to use the service name mysql by default. If a previous installation was not completely removed before installing, this error can be encountered. This occurs because the mysql service already exists on the machine.

Sample

Cannot Create Windows Service for MySQL. Error:0

Resolution

• Choose a different service name when installing.
• On Windows XP or newer, remove the old service with the sc command:
  

  C:\> sc delete mysql
  [SC] DeleteService SUCCESS

• On Windows 2000, download the delsrv.exe tool from http://download.microsoft.com/download/win2000platform/WebPacks/1.00.0.1/NT5/EN-US/delsrv.exe and delete the process with delsrv mysql.

Further Reference

Windows Troubleshooting (MySQL Reference Manual)

MySQL Forums Thread On Error: 0

FAQTs Entry on Error: 0

In MySQL version 4.1, the authentication protocol used for MySQL client-server communications was changed to make it more secure. This changed the format of hashed user passwords and broke compatibility for all clients and APIs designed against MySQL 4.0.

Sample

Warning: mysql_connect(): Client does not support authentication protocol requested by server; consider upgrading MySQL

Resolution

• Upgrade to a 4.1 or higher version of the mysql client.
• Upgrade the API used to one compatible with MySQL 4.1.
  • PHP users can use mysqli or PDO instead of the standard mysql extension. PHP users can also attempt to compile the mysql extension against MySQL 4.1.
  • .NET Users can use Connector/NET instead of Connector/ODBC.
• Run the MySQL server in a mode that uses old password hashing by adding old-passwords to the [mysqld] section of your my.cnf file.
• Update the password of the user who needs to connect from an old-protocol application to use the deprecated password format with this command:
  

  SET PASSWORD FOR ‘user’@'host’ = OLD_PASSWORD(’password’);

Further Reference

Client does not support authentication protocol (MySQL Reference Manual)

Password Hashing as of MySQL 4.1 (MySQL Reference Manual)

mysqli Extension

MySQL APIs (Drivers) for Various Languages