Determining Blobpage Size

When you create a blobspace, use the size of the most frequently occurring simple large object as the size of the blobpage. In other words, choose a blobpage size that wastes the least amount of space. For information on calculating an optimal blobpage size, see blobpage size considerations in the chapter on effect of configuration on I/O activity in the IBM Informix Dynamic Server Performance Guide.

If a table has more than one TEXT or BYTE column, and the objects are not close in size, store each column in a different blobspace, each with an appropriately sized blobpage. See Tables.

Determining Database Server Page Size

When you specify blobpage size, you specify it in terms of the database server pages. You can use one of the following methods to determine the database server page size for your system:

• Run the onstat -b utility to display the system page size, given as buffer size on the last line of the output.
• To view the contents of the PAGE_PZERO reserved page, run the oncheck -pr utility.
• UNIX only: In ON–Monitor, select either the Parameters > Shared-Memory or Parameters > Initialize option to display the system page size.

Obtaining Blobspace Storage Statistics

To help you determine the optimal blobpage size for each blobspace, use the following database server utility commands:

• oncheck -pe
• oncheck -pB

The oncheck -pe command provides background information about the objects stored in a blobspace:

• Complete ownership information (displayed as database:owner.table) for each table that has data stored in the blobspace chunk
• The total number of pages used by each table to store its associated TEXT and BYTE data
• The total free and total overhead pages in the blobspace

The oncheck -pB command lists the following statistics for each table or database:

• The number of blobpages used by the table or database in each blobspace
• The average fullness of the blobpages used by each simple large object stored as part of the table or database

For more information, see Monitoring Blobspace Usage with oncheck -pe, Determining Blobpage Fullness with oncheck -pB, and optimizing blobspace blobpage size in the chapter on table performance considerations in the IBM Informix Dynamic Server Performance Guide.