Loose vs. Tight Replication
In the loose replication model, DATABridge accesses only closed audit files for the DMSII changes. This results in a time delay between a change to the primary database and the corresponding change to the secondary database.
You can control the amount of time between secondary database updates in the following ways:
- Using the AuditTimer utility to schedule audit file closes. For example, you could close the audit file every hour, every day, or even every week, depending on how crucial current information is.
- Using the Copy Audit utility to schedule DATABridge Span to start each time an audit file closes.
- Using the Copy Audit utility or the Notify utility in conjunction with Server Accessory to notify the Client that additional audit file information is available.
- Running the DATABridge Accessory each time you want updates.
In the tight replication model, DATABridge accesses the current audit file for the DMSII changes. Updates to the primary database are performed almost immediately on the secondary database.
By using DATABridge Plus (included with the DATABridge Host software) DATABridge can read the current audit file and provide near real-time updates to the secondary database.
An audit file is created by DMSII and contains the raw format of changes made to the DMSII database by update programs. Audit file records contain the deletes, adds, and modifies that were made to the various structures. It can contain, for example, hours, days, or weeks worth of information.
DATABridge uses the audit file for the raw data of each database change to exactly replicate the primary database. DATABridge records the audit location (AFN, ABSN, SEG, IDX) between runs, so it can restart without losing any records.
If you have DATABridge Plus or you set the DBEngine Read Active Audit option, DATABridge can access the current audit file. If you do not have DATABridge Plus, and you do not set Read Active Audit = true in the DBEngine parameter file, DATABridge can access audit information up to and including the current audit file minus one. Additionally, the audit file contains the update level at the time the audit file was created. The update level in the audit file and the update level in the DESCRIPTION file used by DATABridge must match before DATABridge will update a replicated database.
When an audit file is closed, DMSII creates the next one in the series. Audit files are closed for several reasons, including the following:
- An operator closes the audit file with the mixnumberSM AUDIT CLOSE command
- The audit file reaches the file size set in its DASDL
- There is an I/O error on the audit file
- There is not enough disk space for this audit file
- The database update level changes due to database definition changes
- A DATABridge accessory closed the file in preparation for the fixup phase after extracting records from a DMSII database
- The current audit file could not be found
- A file reorganization was executed to modify the DMSII structure
The Audit Trail
The audit trail consists of the audit files named as follows:
where databasename is the name of the DMSII database, AUDIT is a literal, and nnnn is the AFN, a sequential number between 1 and 9999. For example, if you have a database named BANKDB, an audit file would be named similarly to the following: