Understanding How Essbase Stores Data

To size a database, you must understand the units of storage that Essbase uses. This discussion assumes that you are familiar with the following basic concepts:

An Essbase database comprises many components. In addition to an outline file and data file, Essbase uses several types of files and memory structures to manage data storage, calculation, and retrieval operations.

Table 243 describes the major components to consider when you estimate the disk and memory requirements of a database. “Yes” means the type of storage indicated is relevant, “No” means that it is not.

Table 243. Storage Units Relevant to Calculation of Disk and Memory Requirements

Storage Unit

Description

Disk

Memory

Outline

A structure that defines all elements of a database. The number of members in an outline determines the outline size.

Yes

Yes

Data files

Files in which Essbase stores data values in data blocks in data files.

Named essxxxxx.pag, where xxxxx is a number. Essbase increments the number, starting with ess00001.pag, on each disk volume. Memory is also affected, because Essbase copies the files into memory.

Yes

Yes

Data blocks

Subdivisions of a data file. Each block is a multidimensional array that represents all cells of all dense dimensions relative to a particular intersection of sparse dimensions.

Yes

Yes

Index files

Files that Essbase uses to retrieve data blocks from data files. Named essxxxxx.ind, where xxxxx is a number. Essbase increments the number, starting with ess00001.ind, on each disk volume.

Yes

Yes

Index pages

Subdivisions of an index file. Contain index entries that point to data blocks. The size of index pages is fixed at 8 KB.

Yes

Yes

Index cache

A buffer in memory that holds index pages. Essbase allocates memory to the index cache at startup of the database.

No

Yes

Data file cache

A buffer in memory that holds data files. When direct I/O is used, Essbase allocates memory to the data file cache during data load, calculation, and retrieval operations, as needed. Not used with buffered I/O.

No

Yes

Data cache

A buffer in memory that holds data blocks. Essbase allocates memory to the data cache during data load, calculation, and retrieval operations, as needed.

No

Yes

Calculator cache

A buffer in memory that Essbase uses to create and track data blocks during calculation operations.

No

Yes