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The database schema used by DSpace is created by SQL statements stored in a directory specific to each supported RDBMS platform:

• Wiki MarkupPostgreSQL schemas are in _\[dspace-source\]/dspace/etc/postgres/_unmigrated-wiki-markup
• Oracle schemas are in _\[dspace-source\]/dspace/etc/oracle/_
  The SQL (DDL) statements to create the tables for the current release, starting with an empty database, aer in _database_schema.sql_. The schema SQL file also creates the two required e-person groups (_Anonymous_ and _Administrator_) that are required for the system to function properly.

Wiki MarkupAlso in _\[dspace-source\]/dspace/etc/\[database\]_ are various SQL files called _database_schema_1x_1y_. These contain the necessary SQL commands to update a live DSpace database from version 1._x_ to 1._y_. Note that this might not be the only part of an upgrade process: see Updating a DSpace Installation for details.

The DSpace database code uses an SQL function getnextid to assign primary keys to newly created rows. This SQL function must be safe to use if several JVMs are accessing the database at once; for example, the Web UI might be creating new rows in the database at the same time as the batch item importer. The PostgreSQL-specific implementation of the method uses SEQUENCES for each table in order to create new IDs. If an alternative database backend were to be used, the implementation of getnextid could be updated to operate with that specific DBMS.

The etc directory in the source distribution contains two further SQL files. clean-database.sql contains the SQL necessary to completely clean out the database, so use with caution! The Ant target clean_database can be used to execute this. update-sequences.sql contains SQL to reset the primary key generation sequences to appropriate values. You'd need to do this if, for example, you're restoring a backup database dump which creates rows with specific primary keys already defined. In such a case, the sequences would allocate primary keys that were already used.unmigrated-wiki-markup

Versions of the *_.sql{_}* files for Oracle are stored in _\[dspace-source\]/dspace/etc/oracle_. These need to be copied over their PostgreSQL counterparts in _\[dspace-source\]/dspace/etc_ prior to installation.

Maintenance and Backup

When using PostgreSQL, it's a good idea to perform regular 'vacuuming' of the database to optimize performance. This is performed by the vacuumdb command which can be executed via a 'cron' job, for example by putting this in the system crontab:

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• The fresh_install target loads up the initial contents of the Dublin Core type and bitstream format registries, as well as two entries in the epersongroup table for the system anonymous and administrator groups. Before you restore a raw backup of your database you will need to remove these, since they will already exist in your backup, possibly having been modified. For example, use:

  Code Block
  DELETE FROM dctyperegistry; DELETE FROM bitstreamformatregistry; DELETE FROM epersongroup;
  Wiki Markup

• After restoring a backup, you will need to reset the primary key generation sequences so that they do not produce already-used primary keys. Do this by executing the SQL in _\[dspace-source\]/dspace/etc/update-sequences.sql_, for example with:

  Code Block
  psql -U dspace -f [dspace-source]/dspace/etc/update-sequences.sql

  Future updates of DSpace may involve minor changes to the database schema. Specific instructions on how to update the schema whilst keeping live data will be included. The current schema also contains a few currently unused database columns, to be used for extra functionality in future releases. These unused columns have been added in advance to minimize the effort required to upgrade.

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assetstore.dir =  [dspace]/assetstore

Wiki Markup(Remember that _\[dspace\]_ is a placeholder for the actual name of your DSpace install directory).

The above example specifies a single asset store.

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