Table A (File architecture)

Table A contains three structures: a file dictionary, a set of MANY-VALUED pages, and a set of FEW-VALUED pages. The first of these is a dictionary of the names and attributes of the file's fields and field groups. Some field attributes (notably CODED) require sets of values to be maintained. These values are stored either in the FEW-VALUED or MANY-VALUED attribute structures.

Table A usually is small in relation to the rest of the file.

Internal file dictionary

The internal file dictionary is a hashed file where each page contains as many as ASTRPPG field or field group definitions. The exact number of pages in the internal file dictionary is defined by the ATRPG parameter.

Each entry contains the field code (the representation of the field as physically used in records), the field name, and the field attributes as assigned by the DEFINE FIELD command (or by a redefinition).

To understand all the possible content of any entry, refer to the ZFIELD image (the structure definition is provided with the Model 204 product). This image is populated by the $FDEF or $LSTFLD function.

Non FILEORG X'100' files

The maximum number of fields (the product the ASTRPPG and ATRPG parameter values) in a Model 204 file is 4000, unless the file is defined with the X'100' bit of the FILEORG parameter, as described in the following subsection. This limit might not actually be reached because of wasted entries (where ASTRPPG is defined as too large, you cannot fit the full number on any page) or due to vagaries of the hashing algorithm.

Enhanced Data Handling files (FILEORG X'100' files)

In a FILEORG X'100' file (introduced in version 7.5 of Model 204), the maximum number of fields (ASTRPPG * ATRPG) is 32000.

In order to support this increase as well as to support field groups, the overhead for each field occurrence has increased to 4 bytes (from 3).

Where the maximum number of fields exceeds 4000, no fields can be defined as KEY, NUMERIC RANGE, or FOR EACH VALUE.

MANY-VALUED and FEW-VALUED pages

If a field has the CODED or FRV attribute, a complete list of the values that the field has ever had (since it was last created or reorganized) is held in the FEW-VALUED or MANY-VALUED sets of pages in Table A (MANY-VALUED is the default).

Both of these sets of pages should be kept very small. If large numbers of values exist, the File Manager should consider making the field Ordered.

Parameters related to the use of Table A

ASIZE parameter	The size of Table A (the sum of the values of ATRPG, FVFPG, and MVFPG). View-only.
ASTRPPG parameter	The maximum number of field and field group definitions per page, or the maximum number of field values per page in either the FEW-VALUED or MANY-VALUED section of Table A.
ATRPG parameter	The number of pages containing field and field group definitions.
FVFPG parameter	The number of pages containing FEW-VALUED field values.
MVFPG parameter	The number of pages containing MANY-VALUED field values.