SAND CDBMS Administration Guide
Persistent Mode Operations (Time Travel)

Configuring a Database for Time Travel Operation

Enabling Persistent Mode

To configure a SAND database for Time Travel operation, include the following parameter in the appropriate [DATABASE instance-name] section of the nucleus.ini configuration file, or in the NUCLEUS environment variable:

RunMode=persistent

The next time the database instance is started with the nserv program, a message will indicate that it is running in Persistent Mode, allowing committed changes to the database instance to be saved as permanent Time Travel Update Files by means of the SHUTDOWN...KEEP CHANGE command (see below).

The other relevant parameters in the [DATABASE instance-name] section of the nucleus.ini file (or in the NUCLEUS environment variable) are as follows:

DeltaPath
Specifies the location of the instance's temporary Delta File, in which changes to the database are recorded. This parameter can be overrided by the SnapshotPath paramter.

SnapshotPath
Sets the location for storing the temporary Delta File and new Update Files created via KEEP CHANGE. By default, new Update Files are created in the same directory as the primary database file (specified by the DatabasePath parameter), while the location of the instance's Delta File is given by the DeltaPath parameter. When the SnapshotPath parameter is present, the Delta File and new Update Files are stored in the same directory so that the creation of a new Update File requires only that the Delta File be renamed.

MaxDeltaFileSize or MaxDeltaFileRatio
Specifies the maximum size of the instance's temporary Delta File, in which database changes are recorded. MaxDeltaFileSize specifies this value in megabytes. The default setting for MaxDeltaFileSize is 0, meaning no limit is applied. MaxDeltaFileRatio specifies the maximum file size as a percentage of database size. The default setting for MaxDeltaFileRatio is 0, meaning the MaxDeltaFileSize value is used. If values for both MaxDeltaFileRatio and MaxDeltaFileSize are specified, and the MaxDeltaFileRatio value is not 0, the MaxDeltaFileRatio value is used.

Resolving Update File and Delta File Paths

Given the presence or absence of the SnapshotPath/DeltaPath parameters in a DATABASE section of the nucleus.ini file, the location of the Update/Delta Files is resolved as follows:

• If both SnapshotPath and DeltaPath are specified, SnapshotPath takes precedence: new Update Files and Delta Files are created in the SnapshotPath location.
• If SnapshotPath is specified and DeltaPath is not, new Update Files and Delta Files are created in the SnapshotPath location.
• If SnapshotPath is not specified and DeltaPath is, new Update Files are created in the DatabasePath location and Delta Files are created in the DeltaPath location.
• If neither SnapshotPath nor DeltaPath are specified, new Update Files and Delta Files are created in the DatabasePath location.

Sample nucleus.ini File Entry for a Time Travel Database Instance (UNIX)

[DATABASE customer]
DatabasePath=/usr/sand/db
Cache=256
RunMode=persistent
MaxDeltaFileSize=0
MaxDeltaFileRatio=10
DeltaPath=/usr/sand/delta
SnapshotPath=/usr/upd/db01

When the Time Travel option is enabled, the following line is added to the output from the nserv process when the database instance is successfully started:

where n is the Snapshot number representing the database version being made available for users connecting to this instance of nserv. Snapshot number 0.0 represents the root (original) database.

Connecting to a Time Travel Database Instance

Users connect to a database instance that is running in Persistent Mode in the same way as they would connect to a standard database instance, using the nisqlm utility, SAND Analytic Explorer, or any ODBC-enabled front-end tool. Clients automatically connect to the database Snapshot indicated on database instance start-up.

Managing a Time Travel Database Through SAND Enterprise Manager (Windows Only)

A Time Travel-enabled database can be administered through the SAND Enterprise Manager (SEM) graphical environment. For each Time Travel database, SEM displays the relationship among the different database versions, or Snapshots, in the form of a hierarchical tree structure, with each node identified by its unique number, the date and time of its creation, and an optional user-created label.

SEM supports the following Time Travel operations (in addition to others):

• merging together of Snapshots
  
• deletion of Snapshots
  
• setting the current Snapshot for client connections
  
• relocation of Update Files

For more information, refer to the online help file for SEM.