= Trac Database Schema =

The database schema is defined in [source:/trunk/trac/db_default.py trac.db_default], along with the initial contents of the database, and default configuration values. The schema includes the tables listed below.

|| '''Table Name''' || '''Purpose''' ||
|| `attachment` || Descriptions of attachments (the files themselves are stored on disk). ||
|| `auth_cookie` || User login cookies. ||
|| `component` || Values that can be used in a ticket's "component" field.  The `owner` column is used as the default assignee for new tickets, if not overridden at the time of ticket submission. ||
|| `enum` || Maps integer IDs for issues' priorities, severities, etc. to human-readable names. ||
|| `milestone` || Project milestones. ||
|| `node_change` || 1^st^ half of the repository cache: for every changeset (as identified by the revision number), this table contains the nodes (i.e. files or directories) that have been added/modified/deleted. ||
|| `permission` || Username/action pairs describing who's allowed to do what. This table's contents also hold permission groups. ||
|| `report` || Stores the SQL to generate canned database reports. ||
|| `revision` || 2^nd^ hald of the repository cache: changesets, containing the revision number, author, time, and log message.  The list of files and directories modified by a changeset can be found by joining with `node_change` on the `rev` column. ||
|| `session` || Last user visit time. ||
|| `session_attribute` || Information about user settings, including name, email, and diff options. ||
|| `system` || System information such as the database version and repository cache metadata  ||
|| `ticket` || Tickets. ||
|| `ticket_change` || Changes to tickets, on a field-by-field basis.  The field value `comment` is special: it associates a comment with a set of field changes. ||
|| `ticket_custom` || The values of custom ticket fields. ||
|| `version` || As in `component` and `milestone`, this holds the options of the drop-down `version` list on the ticket form. Every version can have a `time` set, although that is not presently used other than for ordering the list of versions in the UI. ||
|| `wiki` || Wiki pages (including old revisions). ||

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See also: TracDev, TracDev/DatabaseUpgrades