IBM 000-8697 Manual Do Utilizador

IBM Informix OnLine Database Server Administrator’s Guide

A blobpage is the unit of disk space allocation used to store

BYTE

 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 of

BUFFSIZE

, the page size

defined in the configuration file. For more information, refer to

.

A dbspace 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.

The function of the blobspace is to store only

BYTE

and

TEXT

data in the most

efficient way possible. Blobs associated with several different tables all can be
stored within the same blobspace. Blob data that is stored in a blobspace is
written directly to disk and does not pass through shared memory. For more
information, refer to

.

A dbspace or blobspace is composed of one or more chunks. When you create a
dbspace or blobspace, you assign to it one or more primary chunks. You can
add more chunks anytime. One of the key tasks of an OnLine administrator
is to monitor the chunks for fullness and anticipate the need to allocate more
chunks to a dbspace or blobspace.

Dbspaces or blobspaces that are mirrored require one mirror chunk for each
primary chunk. As soon as a mirror chunk is allocated, all space in the chunk
appears as full in the status displays output from tbstat -d or the Dbspaces
menu, Info option.

The initial chunk of the root dbspace and its mirror are the only chunks
created during disk space initialization. The initial chunk of the root dbspace
contains specific reserved pages and internal tables that describe and track all
other dbspaces, blobspaces, chunks, databases, and tblspaces.