Revision as of 09:03, 31 July 2011

Akonadi Server Database Internals

This page contains information about how the Akonadi server uses its internal SQL database. This is purely for Akonadi server developers, you are NOT supposed to use the database yourself, by-passing Akonadi!

Database Schema

• Visualization
• Code is in server/src/storage
  • akonadidb.xml contains the schema in an XML format
  • dbinitializer* contains the code to create tables out of that
  • updatedb.xml contains schema update instructions
  • dbupdater.* executes those

Backends

Akonadi can use different SQL backends. The following documents backend-specific details.

In general, backend specific configuration and setup code can be found in server/src/storage/dbconfig*.

There are three possible operation modes for backends, most only support a subset:

• Embedded: No server process, database is completely integrated into the Akonadi process
• Internal server: Akonadi manages the database server process itself, taking care of starting/stopping and configuring it.
• External server: Akonadi connects to an already running database server.

Selecting and configuring the different backends can be done in ~/.config/akonadi/akonadiserverrc, details on the available options can be found here: akonadiserverrc options

MySQL

Status: working, default backend for desktop systems

Supported modes: Internal, External

MySQL server configuration files for the internal mode can be found here: server/src/storage/mysql-global*.conf.

Sqlite

Status: working with limitations, default backend for mobile systems

Supported modes: Embedded

Known issues:

• Requires newer version than the default Qt one.
• Requires patched QtSql driver to fix concurrency issues (Akonadi ships a fork of the driver with the necessary changes)
• Slower than MySQL (see e.g. http://bertjan.broeksemaatjes.nl/node/53), based on our measurments about 2-5x on the query level, but still in the milliseconds range, so that's probably not a big issue.
• Mutex-based transaction serialization in Akonadi (required due to lack of concurrency support in Sqlite) can block clients while background operations such as a IMAP sync are going on. This is the real killer here, the more clients (including background processes like indexing) are accessing the data, the more blocking you experience.

PostgreSQL

Status: unknown

Supported modes: Internal, External

TODO

Virtuoso

Status: not working

Supported modes: External

Proof-of-concept work was done during Akademy 2010, up to the point where the database could be created successfully. Known issues:

• Some column names used by Akonadi are Virtuoso keywords
• Some of the first INSERT query fails with a signed vs. unsigned int mismatch/overflow.

Completion of Virtuoso support is considered non-trivial and probably requires a lot of work on the Akonadi side, the SQL dialect is too different from what we support so far.

MySQL/Embedded

Status: not working

Supported modes: Embedded

Development stopped, MySQL/Embedded does not support transactions.

Tools

Generic

akonadiconsole has support for browsing the database and run arbitrary SQL queries. See Development/Tutorials/Akonadi/Application.

MySQL

There are convenience scripts for running mysqld in the configuration used by Akonadi as well as (and probably more useful) running the MySQL command line client connected to the Akonadi database. See server/src/storage/akonadi-mysql-[client|server].sh.