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In this section, we explain the storage layer: the database structure, maintenance, and the bistream store and configurations.

RDBMS / Database Structure

DSpace uses a relational database to store all information about the organization of content, metadata about the content, information about e-people and authorization, and the state of currently-running workflows. The DSpace system also uses the relational database in order to maintain indices that users can browse.

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Most of the functionality that DSpace uses can be offered by any standard SQL database that supports transactions. Presently, the browse indices use some features specific to PostgreSQL and Oracle, so some modification to the code would be needed before DSpace would function fully with an alternative database back-end.

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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:

# clean up the database nightly
40 2 * * * /usr/local/pgsql/bin/vacuumdb --analyze dspace > /dev/null 2>&1

The DSpace database can be backed up and restored using usual methods, for example with pg_dump and psql. However when restoring a database, you will need to perform these additional steps:

• 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 epersongrouptable 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:

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  DELETE FROM dctyperegistry; DELETE FROM bitstreamformatregistry; DELETE FROM epersongroup;

• 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.

Configuring the RDBMS Component

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For example, a bitstream with the internal ID 12345678901234567890123456789012345678 is stored in the directory:

(assetstore dir)/12/34/56/12345678901234567890123456789012345678

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Bitstream stores in the file system on the server are configured like this:

assetstore.dir =  [dspace]/assetstore

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The above example specifies a single asset store.

assetstore.dir =  [dspace]/assetstore_0
assetstore.dir.1 = /mnt/other_filesystem/assetstore_1

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By default, newly created bitstreams are put in asset store 0 (i.e. the one specified by the assetstore.dir property.) This allows backwards compatibility with pre-DSpace 1.1 configurations. To change this, for example when asset store 0 is getting full, add a line to dspace.cfg like:

assetstore.incoming = 1

Then restart DSpace (Tomcat). New bitstreams will be written to the asset store specified by assetstore.dir.1, which is /mnt/other_filesystem/assetstore_1 in the above example.

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For example, let's say asset store number 1 will refer to SRB. The there will be a set of SRB account parameters like this:

srb.host.1 = mysrbmcathost.myu.edu
srb.port.1 = 5544
srb.mcatzone.1 = mysrbzone
srb.mdasdomainname.1 = mysrbdomain
srb.defaultstorageresource.1 = mydefaultsrbresource
srb.username.1 = mysrbuser
srb.password.1 = mysrbpassword
srb.homedirectory.1 = /mysrbzone/home/mysrbuser.mysrbdomain
srb.parentdir.1 = mysrbdspaceassetstore

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