Further Reading — Chapter 12: Indexed File Processing (VSAM KSDS)

IBM Official Documentation

DFSMS Access Method Services for Catalogs (IDCAMS) — The definitive reference for defining and managing VSAM clusters, alternate indexes, and paths. Available on the IBM Knowledge Center.
DFSMS Using Data Sets — Chapters on VSAM data set organization, including detailed coverage of CIs, CAs, index structures, and buffer management.
Enterprise COBOL for z/OS: Programming Guide — Chapter on file processing, covering SELECT statements, access modes, and file status codes specific to Enterprise COBOL.
z/OS DFSMS Macro Instructions for Data Sets — Low-level detail on VSAM macros and return codes, useful for understanding extended status codes.

Murach's CICS for the COBOL Programmer by Raul Menendez and Doug Lowe — Excellent coverage of VSAM file processing in the context of online CICS programs, including practical examples of browse and update operations.
VSAM: Access Method Services and Application Programming by Doug Lowe — A focused treatment of VSAM from both the systems programmer and application programmer perspectives.
Advanced COBOL for Structured and Object-Oriented Programming by Gary DeWard Brown — Covers indexed file processing with attention to enterprise patterns and performance considerations.

IBM Z Xplore (https://www.ibm.com/z/resources/zxplore) — Free hands-on mainframe access where you can define and work with real VSAM files.
GnuCOBOL FAQ — Indexed Files — Documentation on how GnuCOBOL implements indexed file support, including configuration options for different back-end storage engines.
VSAM Tutorial on IBM Developer — Step-by-step tutorials covering VSAM cluster definition, loading, and access from COBOL programs.

z/OS DFSMS Using the New Functions — Coverage of VSAM performance enhancements including System-Managed Buffering (SMB) and data striping.
VSAM Demystified (IBM Redbook SG24-6105) — A comprehensive IBM Redbook covering VSAM internals, performance tuning, and best practices for production environments.

Chapter 11: Sequential File Processing — foundational concepts for all file processing
Chapter 13: Relative Files and RRDS — the third VSAM file organization
Chapter 14: Advanced File Techniques — multi-file processing, balanced-line algorithm
Chapter 29: CICS Fundamentals — online VSAM access from CICS transactions
Chapter 38: Batch Processing Patterns — production batch patterns using VSAM files
Appendix E: VSAM and File Organization Reference — quick-reference tables for all VSAM concepts