IBM Version 4 manual User Index APIs, 8APIs-13, Usridx

ŸIt is good practice to periodically (such as once a day) dele data queue at a safe point. Performance can be affected if to exist without being removed. Re-creating the data queue periodica the data queue to its optimal size.

Similarities to Message		Queues:	Data queues are similar to			message		queues,
that programs can send data to a queue and				that	data can			be rec
another program. However, more than one program				can have a receive op
pending on a data queue at the same time, while					only		one program		c
receive operation pending on a message queue				at the same time. (Onl
program receives an entry from a data queue,				even		if	more	than	one
waiting.)	Entries	on a	data queue are handled	in either first-in firs
last-in-first-out, or keyed-queue order. When an				entry		is	received,		it
from the	queue.

User	Queue	APIs
The	user	queue APIs let you create and deleteUser queues user arequeues.
permanent		objects			with	an	object type of *USRQ. They provide a way
more processes				to	communicate asynchronously.
You	can	use	user		queues		to:
Ÿ	Communicate		between			two	processes asynchronously
Ÿ	Store	data in arrival sequence for later use
Ÿ	Contain	keyed		messages
Ÿ	Create	a	batch machine

ŸPermit better performance than the data queue interface

You can save and restore user queues. However, you can only save o definition. You cannot save or restore the messages in it. You cannot user queue if a user queue with the same name already exists in must provide programs to use this object type to enqueue and deque

User Index APIs

The user index APIs allow you to:

Ÿ	Create and delete		user	indexes
Ÿ	Add, retrieve,	and	remove	user	index	entries
Ÿ	Retrieve the	attributes		of a	user	index

A user	index	is	an	object		that allows		search functions for data in th
automatically		sorts data based on the							value of the data. User inde
nent	objects		in	the	user	domain	or	in	the system domain. They have
of	*USRIDX	and		a	maximum	size	of	4	gigabytes (4 294 967 296 bytes).

help streamline table searching, cross-referencing, and ordering of da

general,

if your

table

is

longer

than

1000 entries,

an

index performs

user-sorted

table.

You

can use user indexes to:

Ÿ

Provide

search

functions

Ÿ

Do faster

insert

operations

than in

a

database

file

Ÿ

Do faster retrieve operations than in

a

database file

Ÿ

Create an

index

by

name, such

as

a

telephone

directory

Ÿ

Use

order

entry

programs

Ÿ Look

up

abbreviations

in

an

index

Chapter

8.

Use of

OS/400

8APIs-13