XVSAM logical structure

XVSAM uses the ISAM file Catalog as VSAM master catalog, to keep all information about the structure of data files. Catalog is 400 bytes fixed record length file containing two different kind of records: cluster records and alternate index records with the same structure, but identified by the first character in the record layout, as shown in the following figure:

Field		Length	Cluster record	Alternate index record
CATALOG		44	name of the logical catalog which contains the file	same
CLUSTER		44	cluster name	same
PRIMARY		44	blank	primary cluster name
PATH		80	UNIX directory (see “path convention” below)	blank
TYPE		1	‘K’ - KSDS, ‘R’ - RRDS, ‘E’ - ESDS	‘U’ - unique, ‘D’ - duplicate
RECFORMAT		1	’F’ for fixed-length file or ‘V’ otherwise	blank
RECMIN		5	minimum length of record in C format “%05d”	number of key in C format “%05d”
RECMAX		5	maximum length of record in C format “%05d”	blank
NPARTS		5	key parts number in C format “%05d”	same
8	KEYOFF	5	key offset in C format “%05d”	same
times	KEYLEN	5	key length in C format “%05d”	same
RESERVED		83	Reserved for future using	same

The Catalog file, which is stored in the directory pointed by the XVSAM environment variable, must not be cancelled or moved somewhere else.