Customize size specifications for large objects

Customize the AVG_LO_SIZE and MIN_EXT_SIZE specifications for sbspaces that will contain etx indexes.

An etx index fragment is composed of 6 to 13 smart large objects. The number of smart large objects depends on the combination of WORD_SUPPORT and PHRASE_SUPPORT index parameters used in the CREATE INDEX statement. The following table shows how many smart large objects make up an etx index fragment for each combination of index parameters.


Index parameter combination	Number of smart large objects
WORD_SUPPORT=EXACT, PHRASE_SUPPORT=NONE	6
WORD_SUPPORT=EXACT, PHRASE_SUPPORT=MEDIUM	9
WORD_SUPPORT=EXACT, PHRASE_SUPPORT=MAXIMUM	10
WORD_SUPPORT=PATTERN, PHRASE_SUPPORT=NONE	9
WORD_SUPPORT=PATTERN, PHRASE_SUPPORT=MEDIUM	12
WORD_SUPPORT=PATTERN, PHRASE_SUPPORT=MAXIMUM	13

Important: The default value for the WORD_SUPPORT index parameter is EXACT. The default value for the PHRASE_SUPPORT index parameter is NONE.

As an etx index fragment grows, some of the smart large objects that contain the index also grow. The smart large object extensions that are created as a result can be costly in both access time and consumption of metadata space. If you specify a relatively large MIN_EXT_SIZE value, you minimize the number of these extensions. The default value for MIN_EXT_SIZE is 4 and the default value for AVG_LO_SIZE is 64. Increase these values substantially, to 1000 and 2000, for example.

The following example shows how to specify new values for AVG_LO_SIZE and MIN_EXT_SIZE with the onspaces utility:

% onspaces -c -S sbsp1 -g 2 -p /dev/sbspace -o 0 \
   -s 1000000 -Df "AVG_LO_SIZE=1000,MIN_EXT_SIZE=2000"

The following output from an oncheck -cS sbsp1 command shows the effect of setting these options:

Large Objects
 ID                  Ref   Size       Allocced         Creat    Last
 Sbs#   Chk#   Seq#  Cnt   (Bytes)    Pages    Extns   Flags    Modified
 ----   ----   ----- ---- ---------- --------  -----   -----    ---------------------
    4     4      2     1        25       1      2      L-N-H    Tue Mar  9 15:29:18 1999
    4     4      3     1     33280      25      4      L-N-H    Tue Mar  9 15:29:18 1999
    4     4      4     1    247564     164      4      L-N-H    Tue Mar  9 15:29:18 1999
    4     4      5     1       512       1      2      L-N-H    Tue Mar  9 15:29:18 1999
    4     4      6     1     52340      35      4      L-N-H    Tue Mar  9 15:29:18 1999
    4     4      7     1    131072      65      3      L-N-H    Tue Mar  9 15:29:18 1999

The table whose etx index is stored in the sbspace sbsp1 contains 100,000 documents, averaging 2 KB in size. The number of extensions (Extns) is low.