File access methods

You can use either sequential or VSAM files for DDIO files. Shared directories must be VSAM files. If you are using VSAM files for your DDIO files, you can copy them using the IDCAMS REPRO command. You cannot, however, change any of the file attributes such as CISIZE without reallocating a DDIO/DB file. Allocation and format requirements, along with the steps for preparing the various DDIO files, will vary according to the type of file. Source listing files can be shared between all BMC AMI products that use CSS, while report files, transaction databases, work files, and profile files, cannot. Source listing files used by BMC AMI DevX Code Debug for CICS must be VSAM.

Warning

CWDDSUTL, CWFXSDUT, CWAASDUT, CWDDLPUT, and CWDDALLU are the only utilities recommended for use with BMC DDIO files.

BMC AMI DevX File-AID/MVS and other VSAM-related vendor products (including vendor packages that compress or enhance buffer management on VSAM files) should NOT be used against BMC DDIO files. Doing so can result in corrupting the contents of the DDIO file.

Selecting a file access method

No external functional differences exist in the way these two types of data sets interact with BMC AMI products. The method you choose should be based on your operating system and can be done on a file-by-file basis.

VSAM and sequential DDIO files are processed identically by CSS, and entries can be transferred between files defined with either access method. However, there are advantages and disadvantages to both methods. Since VSAM allocates its buffers above the 16 MB line, CICS users may experience a performance improvement when using VSAM DDIO files. Sequential data set buffers are allocated below the 16 MB line so applications that have many DDIO files open may experience shortages of below-the-line storage.

Disk space and memory usage are also considerations when choosing a file access method. You can define a sequential DDIO file to use disk space more efficiently than a VSAM file. VSAM DDIO files are limited by the multiple of 2K Control Interval Size (CISIZE) restriction. However, VSAM DDIO files utilize CICS memory much better than sequential DDIO files in the CICS environment. (This factor is not as critical in a batch environment.)

Important

Only supported-level releases of BMC AMI DevX Abend-AID are required to use Report Shared Directories.
BMC AMI DevX Code Debug for CICS requires that all source listing DDIO files used in a CICS region be VSAM. All shared directories must be VSAM.

VSAM DDIO files can be copied using the IDCAMS REPRO command but none of the file attributes, such as CISIZE, can be changed.

The following table lists the details of the job names, and the parameters used with those jobs, when allocating or formatting DDIO files.

File	Allocate/Format	Type	JCL Name	Multi-Volume
Source	Allocate	VSAM	CXALLVS	CXDFMSL
	Allocate	Sequential	CXALLDS
	Format	VSAM	CXFMTSL	CXDFMSL
	Format	Sequential	CXFMTSL
BMC AMI DevX Abend-AID Report	Allocate	VSAM	CXALLVS	CXDFMAA
	Allocate	Sequential	CXALLDS
	Format	VSAM	CXFMTAA	CXDFMAA
	Format	Sequential	CXFMTAA
BMC AMI DevX Abend-AID for CICS Shared Directory	Allocate and Format	VSAM	CXALLMC	CXDCRTSD¹
BMC AMI DevX Abend-AID for CICS Transaction Database	Allocate and Format	VSAM	CXALLVSD	CXDCRTDB
BMC AMI DevX Abend-AID for CICS Transaction Database	Allocate and Format	Sequential	CXALLBSD
Source Listing Shared Directory	Allocate and Format	VSAM	CXALLDLP	CXDCRLSD¹
Source Listing Database	Allocate and Format	VSAM	CXALLVLP	CXDCRLDB
Source Listing Database	Allocate and Format	Sequential	CXALLBLP
BMC AMI DevX Abend-AID Shared Directory	Allocate and Format	VSAM	CXALLDAA	CXDCRASD¹
BMC AMI DevX Abend-AID Report Database	Allocate and Format	VSAM	CXALLVAA	CXDCRADB
BMC AMI DevX Abend-AID Report Database	Allocate and Format	Sequential	CXALLBAA

¹This job contains the JCL to create a single volume shared directory and a multi-volume database.

File access methods

Selecting a file access method

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