iX V6.5 (30391-90011)

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Chapter 3 75

Deﬁning a Database

Set Part

(Refer to master set name for more information about search items.)

! (exclamation point) denotes a primary path. Only one path in each detail data set can be

designated as a primary path. If no path is designated as primary, the ﬁrst

unsorted path is the primary path by default. If all of the paths are sorted,

the default primary path is the ﬁrst sorted path.

master set name is the name of a previously deﬁned master data set. When a master set

name follows an item name, the data item is a search item linking the

detail set to the named master. Up to 16 search items can be deﬁned for a

detail data set. If no data items have a master name following them, the

detail is not related to any master. In this case, the combined length of all

data items in the data set must equal or exceed two halfwords.

sort item name is the name of a detail data item of type U, K, or X which is a part of the

data set being deﬁned. A sort item deﬁnes a sorted path. Each entry added

to a chain of a sorted path will be linked logically in ascending order of the

sort item values. If sort item is omitted, the path order is chronological;

that is, new entries are linked to the end of chains. For performance

reasons, sorted chains should be kept short. (Refer to "Sort Items" in

chapter 2.)

maximum capacity is the maximum number of entries allowed in a data set (data

capacity). It must be less than or equal to 2

−1 (2,147,483,647) and is

limited by the size of the entry as well as the maximum size of a data set,

jumbo or non-jumbo. This number can differ from the number of entries

speciﬁed in the schema itself because the capacity of each detail is

adjusted to represent an even multiple of the blocking factor. Selecting a

very large maximum capacity minimizes the chances that the set will run

out of space.

For non-jumbo data sets, if the capacity expansion parameter, initial

capacity, is speciﬁed and is less (not zero) than the maximum capacity, the

data set is enabled for dynamic expansion. Note that specifying initial

capacity for a jumbo data set will generate an error.

blocking factor is the number of data set records in one block. If a value is not speciﬁed, it

is calculated by DBSCHEMA.

initial capacity is the initial capacity for the data set, that is, the number of entries for

which space will be allocated and initialized when the data set is created.

This number must be between 1 and 2

−1 inclusive but must be less than

or equal to the maximum capacity. Specifying initial capacity for a jumbo

data set will generate an error. This parameter should be used to closely

approximate the current volume of data. If it is very low, there can be

frequent expansions leading to severe disk fragmentation. If it is very

high, DBPUT may take a long time to complete which could impact other

database users. The initial capacity is adjusted to represent an even

multiple of the blocking factor. Initial capacity is an optional parameter. If

initial capacity is not speciﬁed, or if initial capacity is either zero or equal

to the maximum capacity, then dynamic capacity expansion is not enabled

for the data set, and maximum capacity is used for the data set ﬁle