IBM Version 4 manual Clear Data Queue Qclrdtaq Retrieve Description, Lifo, Following describes

Data	Queue	APIs
Data	queues		are a	type of system object that you can create, to
level	language		(HLL)	program can send data, and	from which another	HLL p
can	receive		data.	The receiving program can be	waiting for the	data,
receive		the	data	later.

The advantages of using data queues are:

ŸUsing data queues frees a job from performing some work. If the interactive job, the data queue APIs can provide better response decrease the size of the interactive program and its process act (PAG). This, in turn, can help overall system performance. For example,

several work station users enter a transaction that involves updating adding to several files, the system can perform better if the int submit the request for the transaction to a single batch processing

ŸData queues are a fast means of asynchronous communication between jobs. Using a data queue to send and receive data requires less

resource

than

using

database

files,

message

queues,

or

data

areas

and

receive data.

Ÿ

You

can

send

to,

receive

from,

and

retrieve

a

description

of

a

d

any

HLL program. This is done by calling the Send

to

a

Data

Queue

(QSNDDTAQ), Receive from Data Queue (QRCVDTAQ), Retrieve Data Queue

Message

(QMHRDQM),

Clear

Data

Queue (QCLRDTAQ),

and

Retrieve

Data

Queue

Description

(QMHQRDQD)

APIs.

Ÿ

When

receiving

data

from

a

data

queue,

you

can

set a time-out su

job

waits until an entry arrives

on

the

data

queue. This

is

diffe

the

EOFDLY parameter

on

the

Override

Database

File

(OVRDBF)

command,

which

causes

the

job

to

be

activated

whenever

the

delay

time

en

ŸMore than one job can receive data from the same data queue. This

advantage	in	certain		applications	where the	number of entries to be
is greater		than	one	job can handle within		the desired performance
For example, if several printers					are available to print orders, seve
jobs could send requests to a					single data queue. A separate job
printer could receive data from					the data queue in first-in-first-out
first-out	(LIFO),		or	keyed-queue	order.

ŸData queues have the ability to attach a sender ID to each mes placed on the queue. The sender ID, an attribute of the data qu established when the queue is created, contains the qualified job current user profile.

Comparisons with Using		Database	Files	as Queues:			The	following describes
the differences between				using	data		queues	and	database	files:
Ÿ Data	queues	have	been	improved		to	communicate		between	active progra
not to store large volumes of data							or large numbers of entries. For
poses,	use	database files			as	queues.

ŸData queues should not be used for long-term storage or indefinite

data. For this purpose, you should use database files.

ŸWhen using data queues, you should include abnormal end procedures programs to recover any entries not yet completely processed befor system is ended.

8-12System API Programming V4R1