MySQL and its MySQLdb Python bindings

Trac supports the ​MySQL database backend, although there are a couple of #KnownIssues. MySQL is fully integrated in Trac's test suite.

Requirements

MySQL

The recommended versions of MySQL are those from 5.x series and above.

The following MySQL drop-in replacements are also known to work:

• The ​MariaDB variant:
  • tested MariaDB 5.3.3, MySQLdb 1.2.3 and Trac 0.12.3
  • tested MariaDB 10.1.10 (x64), MySQLdb 1.2.5 and Trac 1.0.10dev, 1.2dev
• The ​Percona variant:
  • tested Percona 5.6 with Trac 1.1.4

To avoid Unicode and international character conflicts in Trac, such as international characters turning into question marks with mysterious "Incorrect string value" errors logged, the Trac database must be configured with one of the following character set and collation type pairs:

• utf8 / utf8_bin
• utf8mb4 / utf8mb4_bin

The configuration is specified through the character_set_database and collation_database variables of my.cnf. Additionally, all tables must be of type utf8_bin or utf8mb4_bin collation.

Tables must be created as InnoDB or TokuDB type tables, because Trac uses a transaction mechanism that is not supported by MyISAM tables, see ticket:8067:5 and ​MySQL docs. Be aware that the cluster storage engine NDB introduces some limits for Trac (#8567).

The default_storage_engine and default_tmp_storage_engine variables in my.cnf must be set to one of the storage engines supported by Trac.

A proper database can be created with any MySQL client, like this:

CREATE DATABASE trac DEFAULT CHARACTER SET utf8 COLLATE utf8_bin; 

With MySQL version 5.5.3 and up, you can also select the ​mb4 variant of utf8, which enables you to store any Unicode character, not only those in the ​Basic Multilingual Plane. Note that you'll need at least Trac 0.12.3 for this (#9766).

CREATE DATABASE trac DEFAULT CHARACTER SET utf8mb4 COLLATE utf8mb4_bin; 

To check the character set settings for your database, issue the following commands:

mysql> USE trac;
Database changed
mysql> SHOW VARIABLES WHERE variable_name IN ('character_set_database', 'collation_database');
+------------------------+----------+
| Variable_name          | Value    |
+------------------------+----------+
| character_set_database | utf8     |
| collation_database     | utf8_bin |
+------------------------+----------+
2 rows in set (0.01 sec)

mysql>

If you have for example latin1 or utf8 or utf8_ci collation, then read on to the #Conversion section below on how to change it.

If you are setting a new collation on an existing database, make sure that column collations are converted too:

mysql> SHOW FULL COLUMNS FROM `node_change`;
+-------------+-------------+-----------+-
| Field       | Type        | Collation | 
+-------------+-------------+-----------+-
| rev         | varchar(64) | utf8_bin  | 
| path        | text        | utf8_bin  | 
| node_type   | varchar(32) | utf8_bin  | 
| change_type | varchar(32) | utf8_bin  | 
| base_path   | text        | utf8_bin  | 
| base_rev    | varchar(64) | utf8_bin  | 
+-------------+-------------+-----------+-
6 rows in set (0.00 sec)                  

See #3884 for info about collations.

Usually, you also want to create a user and give this user access to the database created above:

GRANT ALL ON trac.* TO tracuser@localhost IDENTIFIED BY 'password';

The connection string will then be:

mysql://tracuser:password@localhost/trac

MySQLdb

Trac ≥ 1.3.2

For Trac ≥ 1.3.2, ​PyMySQL should be used.

Trac < 1.3.2

The recommended version is ​MySQL-python 1.2.2+, which must be compiled in thread-safe client mode. Earlier versions are known to be problematic.

The ​MySQL-python page on PyPI contains links to the .tar.gz source distribution.

For Windows, there are several possibilities:

• the PyPI page mentioned above also links to pre-built Windows eggs, but for Python 2.7 32-bits only.
• Python binaries (32-bits and 64-bits) can be found at codegood.com ​for Python 2.6 and ​for Python 2.7; these have been last updated in 2010, so it only proposes version 1.2.3, which should however work fine.
• Python 2.7 wheels (32-bits and 64-bits) can be found in the ​Unofficial Windows Binaries for Python Extension Packages, kindly provided by Christoph Gohlke, Laboratory for Fluorescence Dynamics, University of California, Irvine.
• if you are using ActiveState Python 2.6 on Windows, you can install with pypm install mysql-python
• the ​Conda project also contains recent versions of this package and it's handy for use by continuous integration systems as the package can be installed non-interactively using the command conda install -qy mysql-python (32-bits and 64-bits).

On FreeBSD this package is called py-MySQLdb in ​the ports collection.

Thread-safety is important

You should make sure that you are using a thread-safe version of the bindings. To verify this, you can check the System Information section in the About Trac page, when you are logged with a user having the CONFIG_VIEW or the TRAC_ADMIN permission. You should see a line reading: MySQL server: "...", client: "...", thread-safe: 1. If you're seeing thread-safe: 0 instead, the MySQL-python version you're using was not correctly built. Check the following resources to see what you should do:

• ​MySQLdb-1.2.3/MySQLdb/README, see the Building and installing section,
• ​MySQLdb-1.2.3/MySQLdb/site.cfg

Note that even if you build MySQLdb to use the thread-safe libraries, About Trac may still report that it is not thread-safe. If that happens, verify that it is thread-safe by calling MySQLdb.thread_safe() from a standalone Python script, ie not under Apache. If the stand-alone test reports that MySQLdb is indeed thread-safe, then the problem may lie with the PHP module. For example, the Red Hat rpm for PHP is built to use the non-thread-safe MySQL libraries, and the Apache PHP module apparently gets loaded first. So when Python and MySQLdb load, they end up using the already loaded MySQL libraries, which are not thread-safe. The circumvention for this problem is to replace the non-thread-safe libs in /usr/lib/mysql with soft links, so as to have the non-thread-safe lib names point to the thread-safe libs; restart Apache, and now Trac should be running in thread-safe mode.

Conversion Procedures

Convert from MyISAM to InnoDB storage engine

InnoDB is the default storage engine for since MySQL v5.5, but older databases may still use MyISAM. Check which tables use an unsupported storage engine:

SELECT table_name, engine FROM information_schema.tables WHERE table_schema = DATABASE();

For every table in the Trac database which is not InnoDB run the following:

ALTER TABLE `table_name` ENGINE = InnoDB;

Convert to "utf8_bin" collation

First modify the DB collation to ensure new tables will be created properly:

ALTER DATABASE `trac_database` DEFAULT CHARACTER SET utf8 COLLATE utf8_bin;

Then modify the collation for tables. The command below changes the default collation for new columns and converts old columns as well. Run the following for every table:

ALTER TABLE `table_name` CONVERT TO CHARACTER SET utf8 COLLATE utf8_bin;

Known Issues

Still Opened

next-dev-1.7.x milestone tickets:

#13080

Add [trac] mysql_storage_engine option instead of editting my.cnf

next-major-releases milestone tickets:

#6986

MySQL schema changes for performance

#11206

Reduce join in query process

#12390

Attachment table primary key not unique when migrating from SQLite to MySQL

next-stable-1.6.x milestone tickets:

#12097

Add a script to contrib for converting MySQL storage engine

#12363

Support ucs2/utf16/utf32 charset and utf16_bin/utf32_bin collation in MySQL

unscheduled milestone tickets:

#8567

BLOB column can't be used in PRIMARY KEY and maximum ROW size is 8052 on NDB engine

#12143

mysql + InnoDB + auth_cookie == Bad.

Troubleshooting

If you have an issue, such as OperationalError: (2006, 'MySQL server has gone away'), as in #3645, and your web frontend is Apache, you may have conflicting MySQL libraries. Read ​ApplicationIssues#MySQL_Shared_Library_Conflicts. Another possibility is that you've hit MySQL bug 36639, as explained in ticket:3645#comment:48.

Changing collation to utf8 may fail in MySQL 5.0.x on the MyISAM table type and display the "too big" indexes in some Trac tables. Upgrade to a higher version of MySQL and use InnoDB tables, see ticket:3659:5.

#3182

Error when adding or viewing a ticket using MySQL

#3723

Problems with database encoding

#3857

Encoding problem with mysql

#4017

initenv problem with MySQL - Access Denied

#4437

install error (mysql)

#4528

TypeError: unhashable type when installing trac-0.10.3 with mysql

#5012

'module' object has no attribute 'connect'

#6237

InterfaceError: (0, '') after idle period with mod_wsgi 1.1/Apache 2.2.3

#6554

trac-admin allows to init environment with mysql errors

#6787

Trac 0.10.4 - ticket module provider fails in background

#8279

IntegrityError when not logged in

#8552

Formatted time via SQL command FROM_UNIXTIME fails to replace %*

#9696

OperationalError: (2002, "Can't connect to local MySQL server through socket '/var/lib/mysql/mysql.sock' (13)")

#9983

TypeError: int() argument must be a string or a number

#10287

TypeError: unsupported type for timedelta microseconds component: unicode

#10511

OperationalError: (1030, 'Got error 28 from storage engine')

#11727

Problem with synchronizing svn commits to MySQL database

#12409

The $ character must be URL encoded if used as a database password

Also noteworthy:

#4378

MySQL structure case insensitive causes collision with file names

If you get an error from Python when using trac-admin like this:

OperationalError: (1045, "Access denied for user 'tracuser'@'localhost' (using password: YES)")

There are a few possibilities:

1. Try first to login on the command-line using the user tracuser: mysql -p -h localhost -u tracuser
2. Created user is not yet used by MySQL. Login to the MySQL server as root with mysql -p and type: FLUSH PRIVILEGES;
3. The user is added but the host does not match in the MySQL user table (occurred on a FreeBSD setup). Correct this with: mysql -p; use mysql; UPDATE user SET Host="localhost" WHERE User="tracuser"; FLUSH PRIVILEGES;

Ticket numbers are not incrementing by one

The database schema specifies autoincrement for several columns, including the column for ticket IDs. In MySQL, the autoincrement value is configurable and defaults to 1. If the sequence of ticket IDs is not incrementing by 1, the ​auto_increment_increment value in my.cnf probably needs to be changed to 1.