IBM Version 4 manual Performance Considerations, System

Performance Considerations

APIs and Internal

System

Objects

APIs retrieve information from internal

system objects. Some of the inf

contains

special

values. For

example,

the list object

API

returns

the

a

special

value

(*PGM, *LIB,

and

so

on). However,

special

values

may b

in future releases. Even numeric values

may

have

new

special values. W

code to APIs, you should assume that

the

format of

the information

change

from

release to release,

but

the

content

of

the

information

Performance Considerations

The retrieve APIs allow you to control the performance cost for info retrieve. The format specified for any API influences the performanc API. In general, when more information is returned, the performance is

Some

list

APIs,

such as

list

jobs,

list spooled files, and list

objec

with minimal cost. This is

why

these

formats

do

not

retrieve

very muc

Some

of

the APIs,

such

as list record formats and

list fields,

have

because

there

is

no additional performance

cost

to

supply

the

comple

The retrieve APIs, such as retrieve member description and retrieve attributes, have formats that are generally ordered from fastest pe slowest performance. That is, the lower numbered formats run faster b less information, and the higher numbered formats run slower but retri information. One exception is the Retrieve Job Information (QUSRJOBI the order of the formats does not have anything to do with perfor istics. For more information about the performance characteristics for QUSRJOBI API formats, see the Retrieve Job Information (QUSRJOBI Work Management part ofSystemthe API Referencebook.

Chapter 2. Getting Started with2-31APIs