Advanced (Create Table Space) -- Fields and controls

Page size

Extent size

Prefetch size

Overhead

Transfer

Buffer pool

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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.

To change the page size :

• Click on the arrow key to see a list of page sizes and select one.

Extent size

This box contains 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. (The size of a page is selected in the Page size field.)

Initially, this field displays the default value of the dft_extent_sz configuration parameter.

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

• Type the number of extent pages in the box.

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:

• Click the arrow keys to display a list of recommended sizes and select one.
• Type the number of prefetch pages in the box (preferably a multiple of the extent size).

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:

• Click the arrow keys to scroll through a list of recommended times and select one.
• Type the time, in milliseconds, in the box.

Overhead is calculated using the following formula:
OVERHEAD = average seek time in milliseconds + (0.5 * rotational latency)

where:

• 0.5 represents an average overhead of one half rotation
• Rotational latency is calculated, in milliseconds for each full rotation, as follows:

where you:

• Divide by rotations per minute to get minutes per rotation
• Multiply by 60 seconds per minute
• Multiply by 1000 milliseconds per second.

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:

• Click the arrow keys to scroll through a list of recommended times and select one.
• Type the time, in milliseconds, in the box.

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 the arrow keys to scroll through a list of existing names and select one.