Blobpages

A blobpage is the unit of disk-space allocation that the database server uses to store simple large objects (TEXT or BYTE data) within a blobspace. For a description of blobspaces, refer to Blobspaces.

You specify blobpage size as a multiple of the database server page size. Because the database server allocates blobpages as contiguous spaces, it is more efficient to store simple large objects in blobpages that are as close to the size of the data as possible. Figure 36 illustrates the concept of a blobpage, represented as a multiple (three) of a data page.

Figure 36. A Blobpage on Disk

For information about how Dynamic Server structures data stored in a blobpage, see structure of a blobspace blobpage in the disk structures and storage chapter of the IBM Informix Dynamic Server Administrator's Reference.

Just as with pages in a chunk, a certain number of blobpages compose a chunk in a blobspace, as Figure 37 illustrates. A blobpage is always entirely contained in a chunk and cannot cross chunk boundaries.

Figure 37. A Chunk in a Blobspace, Logically Separated into a Series of Blobpages

Instead of storing simple-large-object data in a blobspace, you can choose to store it in a dbspace. However, for a simple large object larger than two pages, performance improves when you store it in a blobspace. Simple large objects stored in a dbspace can share a page, but simple large objects stored in a blobspace do not share pages.

For information on how to determine the size of a blobpage, refer to Determining Blobpage Size.