Using SMS Extended Format for Datacom databases

Products

• Datacom
• Datacom/AD
• Datacom/DB

Issue/Introduction

Can Datacom databases be allocated as SMS Extended Format datasets?

Resolution

Datacom database files for the index and data areas cannot be defined as SMS Extended Format or as Sequential Extended Format. This means that they cannot be defined with the DSNTYPE=EXTSMS Data Class, nor can they be defined with DSNTYPE=EXTREQ or DSNTYPE=EXTPREF or DSORG=PS-E  in the JCL.

Furthermore, DCB parms and sub parms should not be used for allocating a new dataset when using BDAM/EXCP for Datacom data or index areas. The DCB sub parms will be updated automatically once a DBUTLITY INIT is performed after initial allocation of the dataset.

Additional Information

As noted in the z/OS 3.1 version of IBM DFSMS Using Data Sets on page 375, in the section Processing Extended-Format Sequential Data Sets, "Data sets defined as extended-format sequential must be accessed using BSAM or QSAM, and not EXCP or BDAM."

Until recently, Datacom has used only EXCP processing for all database data and index areas (as well as the CXX, LXX and FXX), so these files cannot be defined as Extended-Format. The reason for this exclusion is that extended format changes the internal structure of the data records, and the actual records will not match the DCB characteristics of the dataset. Also, the internal structure of the blocks is changed slightly, so an EXCP-based program would not be able to read the dataset correctly.

Recent enhancements have introduced the use of Linear VSAM processing in addition to the existing BDAM/EXCP processing, and there are special requirements noted in the Datacom documentation for this. For more information about the use of Linear VSAM, please see the Datacom documentation topic VSAM Linear Datasets with Media Manager for the LXX.