Size of the Root Dbspace

To calculate the size of the root dbspace, take the following storage structures into account:

• The physical log (200 kilobytes minimum)
• The logical-log files (200 kilobytes minimum)
• Temporary tables
• Data
• System databases (sysmaster, sysutils, syscdr, sysuuid) and system catalogs (the size varies between versions)
• Reserved pages (~24 kilobytes)
• Tablespace tablespace (100 to 200 kilobytes minimum)
• Extra space

This estimate is the initial root dbspace size before you initialize the database server. The initial size of the root dbspace depends on whether you plan to store the physical log, logical logs, and temporary tables in the root dbspace or in another dbspace. The root dbspace must be large enough for the minimum size configuration during disk initialization.

Recommendation: Set up the system with a small log size (for example, three 1000-kilobyte log files, or 3000 kilobytes for the total log size). After setup is complete, create new dbspaces, move and resize the logical-log files, and drop the original logs in the root dbspace. Then move the physical log to another dbspace. This procedure minimizes the impact of the logs in the root dbspace because:

• A large amount of space is not left unused in the root dbspace after you move the logs (if your root dbspace does not grow).
• The logs do not contend for space and I/O on the same disk as the root dbspace (if your root dbspace does grow).

For details on how to move the logs, see Moving a Logical-Log File to Another Dbspace and Changing the Physical-Log Location and Size.

You can add chunks and drop empty chunks in the root dbspace. Start with a small root dbspace and expand it as your system grows. However, you cannot start with a large initial root chunk and shrink it.

Physical and Logical Logs

The value stored in the ONCONFIG parameter PHYSFILE defines the size of your physical log. Advice on sizing your physical log is contained in Size and Location of the Physical Log.

To calculate the size of the logical-log files, multiply the value of the ONCONFIG parameter LOGSIZE by the number of logical-log files. For advice on sizing your logical log, see Estimating the Size and Number of Log Files.

Temporary Tables

Analyze end-user applications to estimate the amount of disk space that the database server might require for temporary tables. Try to estimate how many of these statements are to run concurrently. The space occupied by the rows and columns that are returned provides a good basis for estimating the amount of space required.

The largest temporary table that the database server creates during a warm restore is equal to the size of your logical log. You calculate the size of your logical log by adding the sizes of all logical-log files.

You must also analyze end-user applications to estimate the amount of disk space that the database server might require for explicit temporary tables.

For more information, including a list of statements that require temporary space, see Temporary Tables.

Critical Data

Recommendation: Do not store databases and tables in the root dbspace. Mirror the root dbspace and other dbspaces that contain critical data such as the physical log and logical logs. Estimate the amount of disk space, if any, that you need to allocate for tables stored in the root dbspace.

Extra Space

Allow extra space in the root dbspace for the system databases to grow, for the extended reserved pages, and ample free space. The number of extended reserved pages depends on the number of primary chunks, mirror chunks, logical-log files, and storage spaces in the database server.