Stored Data Files

The size of the stored database depends on whether the database is compressed and the compression method chosen for the database. Essbase provides five compression-method options: bitmap, run-length encoding (RLE), zlib, index-value, and none.

Calculating the size of a compressed database is complex for a number of reasons including the following:

For a comprehensive discussion of data compression unrelated to estimating size requirements, see Data Compression. The calculations in this discussion are for estimation purposes only.

The calculation for the space required to store the compressed data files (essxxxxx.pag) uses the following factors:

Calculations for No Compression

  To calculate database size when the compression option is none, use the formula:

Number of blocks * (72 bytes + size of expanded data block)

Write the result in cell labeled DE in Table 247, Worksheet: Estimate of Disk Requirements for a Database. Proceed to Index Files.

Calculations for Compressed Databases

Because the compression method used can vary per block, the following calculation formulas are general estimates of the database size. Actual implementation could result in numbers larger or smaller than the calculations.

Bitmap Compression

  To estimate database size when the compression option is bitmap, use the formula:

Number of blocks 
* (72 bytes 
+ (average size in bytes of an expanded data block)
* (1/64 + proportion of cells that are not #MISSING))

For example, if there are 1000 blocks, the average expanded block size is 2000 bytes, and 30% of cells are #MISSING, the result is:

1000 * (72 + 2000 * (1/64 + 0.7) )
= 1000 * 1503
= 1,503,000 bytes (approximately)

Write the result in cell labeled DE in Table 247, Worksheet: Estimate of Disk Requirements for a Database. Proceed to Index Files.

Index-Value Compression

  To estimate database size when the compression option is Index-value, use the formula:

Number of blocks * (72 bytes 
+ (1.5 * database density * expanded data block size)

Write the result in cell labeled DE in Table 247, Worksheet: Estimate of Disk Requirements for a Database. Proceed to Index Files.

RLE Compression

  To estimate database size when the compression option is RLE, use the formula for calculating Bitmap Compression.

When the compression method is RLE, Essbase automatically uses the bitmap or Index-value method for a block if it determines that better compression can be gained. Estimating using the bitmap calculation estimates the maximum size.

Write the result in cell labeled DE in Table 247, Worksheet: Estimate of Disk Requirements for a Database. Proceed to Index Files.

zlib Compression

  To estimate database size when the compression option is zlib, use the formula for calculating Bitmap Compression.

Determining the size of a data block when zlib compression is used is difficult. Individual blocks could be larger or smaller than if compressed using other compression types. Calculating using the bitmap compression formula at least provides an approximation to use for this exercise.

Write the result in cell labeled DE in Table 247, Worksheet: Estimate of Disk Requirements for a Database. Proceed to Index Files.