IBM 000-8697 User Manual

System Architecture

The blobpage contains the blob data. Blobpage size is specified by the OnLine
administrator who creates the blobspace. Blobpage size is specified as a
multiple of the page size: for example, four times

BUFFSIZE

 or 20 times

BUFFSIZE

.

(Refer to

for further information about selecting blobpage size. Refer

to

 for further information about the structure of a blobspace

blobpage.)

Blobs in a blobspace do not share pages. (This differs from the storage
strategy used to store blobs in a dbspace. Refer to

.) OnLine does

not combine whole blobs or portions of a blob on a single blobpage. For
example, if blobspace blobpages are 24 KB, each blob that is 26 KB is stored
on two 24-kilobyte pages. The extra 22 KB of space remain unused.

The structure of a blobpage includes a blobpage header, the blob data, and a
page-ending timestamp. The blobpage header includes, among other infor-
mation, the page-header timestamp and the blob timestamp associated with
the forward pointer in the data row. If a blob is stored on more than one
blobpage, a forward pointer to the next blobpage and another blob
timestamp are also included in the blobpage header. (Refer to

more information about the role of the page-header and page-ending
timestamp pair and the blob timestamp pair.)