Table A (File architecture): Difference between revisions
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A dictionary of the fieldgroup / field names and their attributes. | A dictionary of the fieldgroup / field names and their attributes. | ||
Some attributes (notably '[[Field | Some attributes (notably '[[Field design (File management)#CODED and NON-CODED attributes|CODED]]') require sets of values to be maintained. These values are stored either in the [[Field design (File management)#FEW-VALUED and MANY-VALUED attributes|FEW-VALUED or MANY-VALUED]] attribute structures. | ||
Table A usually is small in relation to the rest of the file. | Table A usually is small in relation to the rest of the file. | ||
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In order to support this increase as well as to support field groups, the overhead for each field occurrence has increased from 3 to 4 bytes. | In order to support this increase as well as to support field groups, the overhead for each field occurrence has increased from 3 to 4 bytes. | ||
Where the maximum number of fields exceeds 4000, no fields can be defined as <var>[[Field | Where the maximum number of fields exceeds 4000, no fields can be defined as <var>[[Field design (File management)#KEY and NON-KEY attributes|KEY]]</var>, <var>[[Field design (File management)#NUMERIC RANGE and NON-RANGE attributes|NUMERIC RANGE]]</var>, or <var>[[Field design (File management)#FOR EACH VALUE (FRV) and NON-FRV attributes|FOR EACH VALUE]]</var>. | ||
== MANY-VALUED and FEW-VALUED pages == | == MANY-VALUED and FEW-VALUED pages == | ||
If a field has the [[Field | If a field has the [[Field design (File management)#CODED and NON-CODED attribute|CODED]] or [[Field design (File management)#FOR EACH VALUE (FRV) and NON-FRV attibute|FRV]] attribute, a complete list of the values that the field has ever had (since it was last created or reorganized) is held in either FEW-VALUED or MANY-VALUED 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. | 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. | ||
Revision as of 20:14, 16 December 2013
Table A contains three structures:
A dictionary of the fieldgroup / field names and their attributes.
Some 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 up to ASTRPPG field or field group definitions. The 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 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 of ASTRPPG * ATRPG) in any Model 204 file is 4000.
Even a number of 4000 or less 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 from 3 to 4 bytes.
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 either FEW-VALUED or MANY-VALUED 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.
ASIZE parameter A view-only parameter containing the size of Table A (the sum of ATRPG + FVFPG + MVFPG). ASTRPPG parameter The maximum number of field / field group definitions per page, or 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 / 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.