IBM 000-8697 User Manual
How to Improve Performance
5-7
Blobpage Average Fullness
The example output indicates that four blobs are stored as part of the table
sriram.catalog
sriram.catalog
. Two blobs are stored in the blobspace blobPIC in 6144-byte
blobpages. Two more blobs are stored in the blobspace bspc1 in 2048-byte
blobpages.
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
blobs. The total says nothing about the size of the blobpages used, the
number of blobs stored, or the total number of bytes stored.
number of blobs 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 blob storage. To
understand how the fullness statistics can improve your blob storage
strategy, it is helpful to use the example in
understand how the fullness statistics can improve your blob storage
strategy, it is helpful to use the example in
average fullness.
Blobpage Average Fullness
The first blob listed in
is stored in blobPIC and requires one 6144-
byte blobpage. The blobpage is 51 to 75 percent full, meaning that the
minimum blob size must be greater than 50 percent of 6144 bytes, or 3072
bytes. The maximum size of this blob must be less than or equal to 75 percent
of 6144 bytes, or 4508 bytes.
minimum blob size must be greater than 50 percent of 6144 bytes, or 3072
bytes. The maximum size of this blob must be less than or equal to 75 percent
of 6144 bytes, or 4508 bytes.
The second blob listed under blobspace blobPIC requires two 6144-byte
blobpages for storage, or a total of 12,288 bytes. The average fullness of all
allocated blobpages is 51 to 75 percent. Therefore, the minimum size of the
blob must be greater than 50 percent of 12,288 bytes, or 6144 bytes. The
maximum size of the blob must be less than or equal to 75 percent of 12,288
bytes, or 9216 bytes. Notice that average fullness does not mean that each
page is 51 to 75 percent full. A calculation would yield 51 to 75 percent
average fullness for two blobpages where the first blobpage is 100 percent
full and the second blobpage is 2 percent full.
blobpages for storage, or a total of 12,288 bytes. The average fullness of all
allocated blobpages is 51 to 75 percent. Therefore, the minimum size of the
blob must be greater than 50 percent of 12,288 bytes, or 6144 bytes. The
maximum size of the blob must be less than or equal to 75 percent of 12,288
bytes, or 9216 bytes. Notice that average fullness does not mean that each
page is 51 to 75 percent full. A calculation would yield 51 to 75 percent
average fullness for two blobpages where the first blobpage is 100 percent
full and the second blobpage is 2 percent full.
Next, consider the two blobs in blobspace bspc1. These two blobs appear to
be nearly the same size. Both blobs require two 2048-byte blobpages and the
average fullness for each is 76 to 100 percent. The minimum size for these
blobs must be greater than 75 percent of the allocated blobpages, or 3072
bytes. The maximum size for each blob is slightly less than 4096 bytes
(allowing for overhead).
be nearly the same size. Both blobs require two 2048-byte blobpages and the
average fullness for each is 76 to 100 percent. The minimum size for these
blobs must be greater than 75 percent of the allocated blobpages, or 3072
bytes. The maximum size for each blob is slightly less than 4096 bytes
(allowing for overhead).