Calculating the Calculator Cache Size

The optimum size of the calculator cache depends on the memory that the system has available and on the nature and configuration of the database.

Using the following formula, you can calculate the calculator cache size required for Essbase to choose each of the three options in Table 175, Calculator Cache Options:

Calculator cache = Bitmap size in bytes * Number of bitmaps

where

Bitmap size in bytes = Max ((member combinations on the bitmap dimensions / 8), 4)

and where

Number of bitmaps = Maximum number of dependent parents in the anchoring dimension + 2 constant bitmaps

Note:

The minimum bitmap size is 4 bytes. If (member combinations on the bitmap dimensions/8) is less than 4 bytes, Essbase uses a bitmap size of 4 bytes.

Consider a sample database with five sparse dimensions (S1 to S5), as shown in Table 176:

Table 176. Example: Sample Database with Five Sparse Dimensions

Sparse Dimension

Number of Members

Dependent Parents

S1

20

Not applicable

S2

20

Not applicable

S3

50

Not applicable

S4

50

Not applicable

S5

200

3

Use this sample database for the following sample calculations:

Option 1: Single Anchoring Dimension, Multiple Bitmaps

For this sample calculation, assume the following facts about a database (from Table 175, Calculator Cache Options):

  • Bitmap dimensions: S1, S2, S3, S4

  • Anchoring dimension: S5

  • Dependent parents in anchoring dimension: 3

Perform this calculation:

Bitmap size in bytes = (S1 * S2 * S3 * S4) / 8
                     = (20 * 20 * 50 * 50) / 8
                     = 125,000 bytes

Number of bitmaps = Maximum number of dependent parents in the anchoring dimension
                  = + 
                  = 2 constant bitmaps
                  = 3 + 2
                  = 5

Calculator cache = Bitmap size * Number of bitmaps
                 = 125,000 * 5
                 = 625,000 bytes

For Essbase to use multiple bitmaps for this database with one anchoring dimension, the calculator cache must be 625,000 bytes.

Option 2: Single Anchoring Dimension, Single Bitmap

For this sample calculation, assume the following facts about a database (from Table 175, Calculator Cache Options):

  • Bitmap dimensions: S1, S2, S3, S4

  • Anchoring dimension: S5

  • Dependent parents in anchoring dimension: Not applicable

Perform this calculation:

Bitmap size in bytes = (S1 * S2 * S3 * S4) / 8
                     = (20 * 20 * 50 * 50) / 8
                     = 125,000 bytes

Number of bitmaps = Single bitmap
                  = 1

Calculator cache = Bitmap size * Number of bitmaps
                 = 125,000 * 1
                 = 125,000 bytes

For Essbase to use a single bitmap for this database with one anchoring dimension, the calculator cache must be 125,000 bytes.

Option 3: Multiple Anchoring Dimensions, Single Bitmap

For this sample calculation, assume the following facts about a database (from Table 175, Calculator Cache Options):

  • Bitmap dimensions: S1, S2, S3

  • Anchoring dimensions: S4, S5

  • Dependent parents in anchoring dimensions: Not applicable

Perform this calculation:

Perform this calculation:

Bitmap size in bytes = (S1 * S2 * S3) / 8
                     = (20 * 20 * 50) / 8
                     = 2,500 bytes

Number of bitmaps = Single bitmap
                  = 1

Calculator cache = Bitmap size * Number of bitmaps
                 = 2,500 * 1
                 = 2,500 bytes

For Essbase to use a single bitmap for this database with multiple anchoring dimensions, the calculator cache must be 2,500 bytes.