All the persistent variable settings are stored in the DDC, which stands for "Dbvisit Database Configuration". This comes in two flavors:
- DDC file: a text file stored on the filesystem
- DDC DB: a table in an Oracle database, by default the MINE database is used
The DDC DB is optional; if it is used, DDC file contains only credentials to the database:
- DDC_DATABASE
- DDC_USER
- DDC_PASSWORD
- DDC_SCHEMA
- TNS_ADMIN
- ORACLE_HOME
- and instruction to load the rest from DDC DB (LOAD DDCDB command).
If the DDC DB is not used, the DDC file contain all variable settings. The main purpose of DDC DB is to enable easier setting changes – issuing a SET command updates the setting in database, obliterating the need to edit the DDC files on every machine.The DDC DB can contain any variable, except those listed above that must be known in order to connect to the DDC database. When DDC DB is used, the SET command automatically updates the DDC DB. If this is not desired, MEMORY_SET command can be used to set the setting in memory only.
This is useful for temporary variable setting in scripts, when the variable change is not meant to be persistent. Note that MINE_UNIQUE_ID variable is set by the -setup.dbvrep script and if DDC DB is not used, DDC file must be manually updated with the new value. The purpose of this variable is to distinguish between repeated runs of setup scripts.The dbvrep parameter --no-ddcdb (or --noddcdb) disables the LOAD DDCDB command. This is used for the first time startup, when the DDC DB is yet to be created and thus LOAD DDCDB would fail.
DDC Commands
A DDC file can be created from the DDCDB. The command is:
CREATE DDCFILE filename FROM DDCDB
The DDC file will be created in the filename specified.
A DDC DB can be created from a DDC file. The command is:
CREATE DDCDB FROM DDCFILE
This takes the active DDC file that dbvrep has been loaded with (through readddc or --ddfile commands) and loads the settings into the DDC DB.
DDC_BACKUP_DIR
On every startup of a process a backup of all DDC settings is made into the DDC_BACKUP_DIR directory as a backup, e.g. for use with CREATE DDCDB FROM DDCFILE, or just for reference.