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1-42 IBM Informix OnLine Database Server Administrator’s Guide
OnLine Disk Space Allocation
Calculate Root dbspace Size
Analyze your application to estimate the amount of disk space that OnLine
might require for implicit temporary tables, which are tables OnLine creates
as part of processing. Implicit temporary tables are stored in the root dbspace
and deleted when the database server process ends.
The following types of statements require temporary tblspace:
■ Statements that include a GROUP BY clause
■ Statements that include subqueries
■ Statements that use distinct aggregates
■ Statements that use auto-index joins
Try to estimate how many of these statements will run concurrently. Estimate
the size of these temporary tblspaces by estimating the number of values
returned.
Enter this value in the field labeled E under ROOTSIZE on the configuration
worksheet (page 1-21).
Next, decide if users will store databases or tables in the root dbspace. One
advantage to root dbspace storage is that the dbspace is usually mirrored. If
root dbspace is the only dbspace 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 will allocate for root
dbspace tables. Enter this value in the field labeled F under ROOTSIZE on the
worksheet (page 1-21).
Now calculate the size of the root dbspace, using the fields A through J that
appear on the first page of the configuration worksheet.
The amount of disk space required for OnLine control information is 3
percent of the size of the root dbspace, plus 14 pages, expressed as kilobytes
(or 14 x BUFFSIZE).
Complete the worksheet calculations to arrive at the size of the initial chunk
for the root dbspace. Enter this value in two places on the configuration
worksheet. First, enter it as the size of the root dbspace in the ROOTSIZE field.
Second, enter it into the field labeled Size of the root dbspace, on the second
page, under the heading Disk Layout.