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System Architecture 2-149
Structure of a Blobspace Blobpage
Blobpage
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 page 5-5 for further information aboutselecting blobpage size. Refer
to page 2-148 for further information about the structure of a blobspace
blobpage.)
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 page 2-145.) 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 page 2-44 for
more information about the role of the page-header and page-ending
timestamp pair and the blob timestamp pair.)