IBM 000-8697 Blobpage, Dbspace and Blobspace

2-84 IBM Informix OnLine Database Server Administrator’s Guide
OnLine Disk Space Terms and Definitions
Blobpage
Ablobpage is the unit of disk space allocation used to storeBYTE and TEXT
data within a blobspace. The size of a blobpage is selected by the user who
creates the blobspace; the size of a blobpages can vary from blobspace to
blobspace. Blobpage is specified as a multiple ofBUFFSIZE, the page size
defined in the configuration file. For more information, refer topage 2-147.
Adbspace contains databases and tables. You can store BYTE and TEXT data
within a dbspace, but if the blobs are larger than two dbspace pages, perfor-
mance can suffer.
Thefunction of the blobspace is to store only BYTE and TEXT data in the most
efficientway possible. Blobs associated with several different tables all can be
stored within the same blobspace. Blob data that is stored in a blobspace is
writtendirectly to disk and does not pass through shared memory. For more
information, refer topage 2-78.
Dbspace and Blobspace
Adbspaceor blobspace is composed of one or more chunks. When you create a
dbspaceor blobspace, you assign to it one or more primary chunks. You can
addmore chunks anytime. One of the key tasks of an OnLine administrator
isto monitor the chunks for fullness and anticipate the need to allocate more
chunks to a dbspace or blobspace.
Dbspacesor blobspaces that are mirrored require one mirror chunk for each
primarychunk. As soon as a mirror chunk is allocated, all space in the chunk
appears as full in the status displays output fromtbstat -d or the Dbspaces
menu, Info option.
The initial chunk of the root dbspace and its mirror are the only chunks
createdduring disk space initialization. The initial chunk of the root dbspace
containsspecific reserved pages and internal tables that describe and track all
other dbspaces, blobspaces, chunks, databases, and tblspaces.