IBM AS/400 manual Record Blocking and Unblocking, ¹ A, Using Externally Described Disk Files

Using Externally Described Disk Files

¹ A	search argument cannot refer	to	a portion of	a	key	field.
If	a search argument refers to	a	partial key,	the	file	is positi

that satisfies the search argument or the record retrieved is the

satisfies the search argument. For			example,	the SETGT and SETLL	operati
position	the file	at the first record on the access path			that	sa
and the	search	argument. The CHAIN	operation	retrieves the	first	re

access path that satisfies the search argument. The DELETE operation first record on the access path that satisfies the search argumen

operation		retrieves the		next record if the portion of the key of
record of the specified type) on					the	access	path matches	the se
READPE	operation		retrieves	the prior record if the portion of the ke
(or the record of the				specified	type) on the		access path matche
ment.	For	more	information	on the above		operation ILEcodes,RPG forsee		the
AS/400	Reference.

Record Blocking and Unblocking

By default, the RPG compiler unblocks input records and blocks output improve run-time performance in SEQ or DISK files when the following cond are met:

1.The file is program-described or, if externally described, it h format.

2. The keyword RECNO is not used in the file-description specificatio

Note: If	RECNO	is	used, the	ILE	RPG	compiler		will not	allow record
However,		if	the file	is an	input		file	and RECNO is used, Da
ment	may	still	block records if fast sequential access is se
that	updated		records	might	not	be	seen	right	away.

3.One of the following is true: a. The file is an output file.

b. If the file is a combined file, then it is an array or ta

c. The file is an input-only file; it is not a record-address fi record-address file; and uses only the OPEN, CLOSE FEOD, and READ file operations. (In other words, the following file operations READE, READPE, SETGT, SETLL, and CHAIN.)

The RPG compiler generates object program code to block and unblock r

all SEQ or DISK files that satisfy the above			conditions. Certain OS/40
restrictions may prevent blocking and		unblocking.	In those	cases,	perfo
not	improved.
You	can explicitly request record	blocking by	specifying	the	keyword

on the file-description specification for the file. The only differe default record blocking and user-requested record blocking is that w

BLOCK(*YES) is specified for input					files,	then the operations SETLL, SETGT
CHAIN	can	be used with the input			file	(see condition 3c above) and
still	occur. If		the	BLOCK keyword	is not specified and these opera
no record		blocking	will	occur.

You can also prevent the default blocking of records by specifying BLOCK(*NO) on the file-description specification. If BLOCK(*NO) is specif

Chapter 16. Accessing Database 287Files