Determine blobpage fullness with oncheck -pB output

The oncheck -pB command displays statistics that describe the average fullness of blobpages. These statistics provide a measure of storage efficiency for individual simple large objects in a database or table.

If you find that the statistics for a significant number of simple large objects show a low percentage of fullness, the database server might benefit from changing the size of the blobpage in the blobspace.

Both the oncheck -pB and onstat -d update commands display the same information about the number of free blobpages. The onstat -d update command displays the same information as onstat -d and an accurate number of free blobpages for each blobspace chunk.

Execute oncheck -pB with either a database name or a table name as a parameter. The following example retrieves storage information for all simple large objects stored in the table sriram.catalog in the stores_demo database:
oncheck -pB stores_demo:sriram.catalog 

oncheck -pB Output

Figure 1 shows the output of this command.
Figure 1. Output of oncheck -pB
              BLOBSpace Report for stores_demo:sriram.catalog

Total pages used by table            7

BLOBSpace usage:
Space   Page             Percent Full
Name    Number    Pages  0-25%  26-50%  51-75  76-100%
-------------------------------------------------------------
blobPIC 0x300080  1      x
   blobPIC 0x300082  2      x
         ------
Page Size is 6144      3

bspc1   0x2000b2  2             x
bspc1   0x2000b6  2                     x
              ------
Page Size is 2048      4

Space Name is the name of the blobspace that contains one or more simple large objects stored as part of the table (or database).

Page Number is the starting address in the blobspace of a specific simple large object.

Pages is the number of the database server pages required to store this simple large object.

Percent Full is a measure of the average blobpage fullness, by blobspace, for each blobspace in this table or database.

Page Size is the size in bytes of the blobpage for this blobspace. Blobpage size is always a multiple of the database server page size.

The example output indicates that four simple large objects are stored as part of the table sriram.catalog. Two objects are stored in the blobspace blobPIC in 6144-byte blobpages. Two more objects are stored in the blobspace bspc1 in 2048-byte blobpages.

The summary information that appears at the top of the display, Total pages used by table is a simple total of the blobpages needed to store simple large objects. The total says nothing about the size of the blobpages used, the number of simple large objects stored, or the total number of bytes stored.

The efficiency information displayed under the Percent Full heading is imprecise, but it can alert an administrator to trends in the storage of TEXT and BYTE data.


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