Table A (File architecture): Difference between revisions
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Some attributes (notably '[[CODED field attribute|CODED]]') require lists of values to be maintained. These lists are stored either in the [[FEW-VALUED field attribute|FEW-VALUED]] or [[MANY-VALUED field attribute|MANY-VALUED]] structures. | Some attributes (notably '[[CODED field attribute|CODED]]') require lists of values to be maintained. These lists are stored either in the [[FEW-VALUED field attribute|FEW-VALUED]] or [[MANY-VALUED field attribute|MANY-VALUED]] 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. | ||
== Internal File Dictionary == | == Internal File Dictionary == | ||
The internal file dictionary is a hashed file where each page contains up to [[ASTRPPG parameter|ASTRPPG]] field or field group definitions. | |||
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). | |||
=== Non [[FILEORG parameter|FILEORG]] x'100' Files === | === Non [[FILEORG parameter|FILEORG]] x'100' Files === | ||
The maximum number of fields (the sum of [[ASTRPPG parameter|ASTRPPG]] * [[ATRPG parameter|ATRPG]]) in any Model 204 file is 4000. | |||
Even when the product of the above is 4000, this number may not actually be reached because of wasted entries (where ASTRPPG is defined too large) or due to vagaries of the hashing algorithm. | |||
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=== [[FILEORG parameter|FILEORG]] x'100' Files === | === [[FILEORG parameter|FILEORG]] x'100' Files === | ||
With the introduction of X'100'files (in Model 204 V7R5) the maximum number of fields ([[ASTRPPG parameter|ASTRPPG]] * [[ATRPG parameter|ATRPG]]) | With the introduction of X'100'files (in Model 204 V7R5) the maximum number of fields ([[ASTRPPG parameter|ASTRPPG]] * [[ATRPG parameter|ATRPG]]) has been increased to 32000. In order to support this increase, as well as the additional attributes. the field code has been increased from 2 to three bytes. | ||
Where the maximum number of fields exceeds 4000, no fields may be defined as [[KEY Field Attribute|KEY]] or [[NUMERIC RANGE Field Attribute|NUMERIC RANGE]]. | |||
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== Many and Few Valued Pages == | == Many and Few Valued Pages == | ||
If a field has the [[CODED field attribute|CODED]] or [[FOR EACH VALUE field 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 (with the latter the default). | |||
Both of these sets of pages should be kept very small. | |||
Revision as of 04:17, 20 March 2013
Table A contains three structures:
A dictionary of the fieldgroup / field names and their attributes.
Some attributes (notably 'CODED') require lists of values to be maintained. These lists are stored either in the FEW-VALUED or MANY-VALUED 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.
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).
Non FILEORG x'100' Files
The maximum number of fields (the sum of ASTRPPG * ATRPG) in any Model 204 file is 4000.
Even when the product of the above is 4000, this number may not actually be reached because of wasted entries (where ASTRPPG is defined too large) or due to vagaries of the hashing algorithm.
FILEORG x'100' Files
With the introduction of X'100'files (in Model 204 V7R5) the maximum number of fields (ASTRPPG * ATRPG) has been increased to 32000. In order to support this increase, as well as the additional attributes. the field code has been increased from 2 to three bytes.
Where the maximum number of fields exceeds 4000, no fields may be defined as KEY or NUMERIC RANGE.
Many 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 (with the latter the default).
Both of these sets of pages should be kept very small.