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2-84 IBM Informix OnLine Database Server Administrator’s Guide
OnLine Disk Space Terms and Definitions
Blobpage
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 page 2-147.
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.
Thefunctionof the blobspace istostoreonly BYTE andTEXT datainthemost
efficientwaypossible.Blobsassociatedwithseveraldifferenttablesallcanbe
stored within the same blobspace. Blob data that is stored in a blobspace is
written directly todisk and does not passthrough shared memory. Formore
information, refer to page 2-78.
Dbspace and Blobspace
Adbspace or blobspaceiscomposed of oneormorechunks.When youcreatea
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 monitorthe chunksfor fullness andanticipate theneed to allocatemore
chunks to a dbspace or blobspace.
Dbspaces or blobspaces that are mirrored require one mirror chunk for each
primarychunk. As soon asamirrorchunk is allocated, allspaceinthechunk
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
createdduringdiskspaceinitialization. The initialchunkoftherootdbspace
containsspecificreservedpagesandinternaltablesthatdescribeandtrackall
other dbspaces, blobspaces, chunks, databases, and tblspaces.
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