Advanced (Alter Table Space) -- Fields and controls

" " Page size
" " Extent size
" " Prefetch size
" " Overhead
" " Transfer
" " Buffer pool
" " OK
" " Show SQL
" " Cancel



" " Page size

This box contains the size of the pages used for the table space. The valid values are 4KB, 8KB, 16KB, and 32KB. The default is a 4KB page size. Using a larger page size allows you to create a table with more columns.

The page size of the table space must be the same as the page size of the buffer pool associated with the table space. If a long table space is defined then the page size must be 4KB.

You cannot alter the page size.

" " Extent size

This box displays the number of pages that are written to a container before the database manager skips to the next container. The database manager uses this value to cycle through the containers as data is stored.

You cannot alter extent size.

" " Prefetch size

This box contains the number of pages that are read from the table space when data prefetching is being performed. Initially, it displays the default value of the dft_prefetch_sz configuration parameter.

To change the prefetch size, use one of these methods:

" " Overhead

This box contains the time, in milliseconds, to use as the I/O controller overhead, and the disk seek and latency time during query optimization.

If this time is not the same for all containers in the table space, the value used should be an average of the overhead time for all containers.

To change the overhead time, use one of these methods:

Overhead is calculated using the following formula: 

overhead = avg seek time in milliseconds + ( ( ( 1 / rotation spe
ed in RPM )

" " Transfer

This box contains the time, in milliseconds, required to read one 4 KB page into memory. It is used to determine the cost of I/O during query optimization.

If this time is not the same for all containers in the table space, the value used should be an average of the transfer time for all containers.

To change the time, use one of these methods:

Transfer is calculated using the following formula: 

transfer = ( 1 / transfer rate in MB per second ) * 1000 / 102400
0 * 4096

" " Buffer pool

Use this box to specify the name of the buffer pool the table space will use to cache table data. If you do not specify a name, the table space will use the default buffer pool.

To select a buffer pool, click on the arrow keys to scroll through a list of existing names and select one.