The cache structure together with the lock structure are used to implement a directory-only caching mechanism at the row level, to allow IOA to speed up the resolution of shared Type 2 database variables directly from the ECSA, without the need to get the last value from the Coupling Facility.

The following formulas illustrate how to calculate the space requirements for the Cache structure:

• total_bytes = total-number-of-variables x 64 x 2

  Where

  total-number-of-variables = rows2 x db2

  and the values for rows and db are according to the number of rows and databases of Type 2.

  Type 1 databases do not require cache or lock storage, because there is no need to validate records.

  Type 2 databases require cache and lock storage that are directly proportional to the number of rows in the database.

  The result is multiplied by 64 because it is assumed that on the average 64 bytes are required per row.

  The result is multiplied by 2 because each database needs temporary space for holding the entire database when a LOADGLOBAL operation is performed. See explanation below.

• blocks = total_bytes/1024 (rounded up to a multiple of 4)

  The result is divided by 1024 and then rounded up to next multiple of 4, since the space requested by CFRM policy is in units of 1 Kbytes and the space required by Control-O/CMEM on startup is in units of 4Kbytes.

The Lock structure exists for Type 2 databases only and the space calculations are the same as for the Cache structure.

Note: The definition of the maximum number of rows can be changed in the IOA ON-LINE PRIMARY OPTION MENU via the IV screen in ADMIN mode, with the U option for the database. The number of columns can be seen in the IV screen in ADMIN mode when selecting the database (pool).