You can estimate the number of bytes of temporary space
needed for an entire index build.

To estimate the amount of temporary space needed for
an index build, perform the following steps:

- Add the total widths of the indexed columns or returned
values from user-defined functions. This value is referred to as
*colsize*.
- Estimate the size of a typical item to sort with one of
the following formulas, depending on whether the index is attached
or not:
- For a nonfragmented table and a fragmented table with
an index created without an explicit fragmentation strategy, use the
following formula:
`sizeof_sort_item = `*keysize* + 4

- For fragmented tables with the index explicitly fragmented,
use the following formula:
`sizeof_sort_item = `

*keysize* + 8

- Estimate the number of bytes needed to sort with the following
formula:
`temp_bytes = 2 * (`*rows* *
*sizeof_sort_item*)

This formula uses the factor `2` because
everything is stored twice when intermediate sort runs use temporary
space. Intermediate sort runs occur when not enough memory exists
to perform the entire sort in memory.

The value for *rows* is
the total number of rows that you expect to be in the table.