To calculate the size of the root dbspace, take the following storage structures into account:
You need not store the physical log, the logical log, or the temporary tables in the root dbspace. Include calculations for these items only if you plan to continue to store them in the root dbspace.
If you plan to move the physical and logical logs, the initial configuration for the root dbspace might differ markedly from the final configuration. You can resize the root dbspace after you remove the physical and logical logs. However, the root dbspace must be large enough for the minimum size configuration during disk initialization.
The sections that follow discuss each storage structure in the root dbspace.
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 Size and Number of Logical-Log Files.
Analyze end-user applications to estimate the amount of disk space that the database server might require for implicit temporary tables. Temporary Tables contains a list of statements that require temporary space. 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 database server creates implicit temporary files when you perform a warm restore. The largest implicit temporary file 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 multiplying the value of LOGSIZE by LOGFILES. For more information on these configuration parameters, see Size and Number of 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. See Temporary Tables.
By default, the database server stores both implicit and explicit temporary tables in the root dbspace. However, if you decide not to store your temporary tables in the root dbspace, you can use the DBSPACETEMP environment variable and configuration parameter to specify a list of dbspaces for temporary files and tables. See Storage of Temporary Tables.
Next, decide if users store databases or tables in the root dbspace. If the root dbspace is the only dbspace that you intend to mirror, place all critical data there for protection. Otherwise, store databases and tables in another dbspace.
Estimate the amount of disk space, if any, that you need to allocate for tables stored in the root dbspace.
The total amount of disk space required for the database server control information is 3 percent of the size of the root dbspace (sum of physical and logical log, temporary space, and data) plus 25 pages, expressed as kilobytes (or 25 times the database server page size).
Each coserver stores information about the current coserver-configuration in a portion of the root dbspace called the safewrite area. Storing this data in the root dbspace ensures data consistency across coservers in the event of a failure. You can use the CONFIGSIZE, MAX_CHUNKS, MAX_DBSPACES, and MAX_DBSLICES configuration parameters to specify the size of the safewrite area. For more information about these parameters, refer to the chapter on configuration parameters in the IBM Informix: Administrator's Reference.
If you run out of space for the safewrite area, the database server writes a message to the transaction log. To increase the amount of space in the safewrite area, add a chunk to the root dbspace before you restart the database server.
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