Learn how to integrate VSAM files with CICS applications effectively. Master FCT entries, CI/CA sizing, performance tuning, and best practices for optimal VSAM performance in CICS environments.
VSAM (Virtual Storage Access Method) is the primary file system for CICS applications, providing high-performance, indexed access to data. Proper integration ensures optimal performance, reliability, and maintainability of your CICS applications.
Optimized VSAM integration delivers fast data access and efficient resource utilization.
Robust error handling and recovery mechanisms ensure data integrity and system stability.
Proper design supports growth in data volume and concurrent user access.
Understanding VSAM basics is essential for effective CICS integration. VSAM provides three main file organizations: KSDS (Key Sequenced Data Set), ESDS (Entry Sequenced Data Set), and RRDS (Relative Record Data Set).
Structure: Index + Data components
Access: Random by key, sequential
Use Case: Customer files, lookup tables
Performance: Fast key-based access
Structure: Data component only
Access: Sequential, relative record
Use Case: Log files, audit trails
Performance: Fast sequential access
Structure: Fixed-length records
Access: Relative record number
Use Case: Direct access files
Performance: Fast direct access
Control Interval (CI):
Control Area (CA):
The File Control Table (FCT) defines how CICS accesses VSAM files. Proper FCT configuration is crucial for performance, security, and error handling in VSAM operations.
File Name: Logical name used in programs
Dataset Name: Physical VSAM file name
Access Method: VSAM, QSAM, or other
File Status: Enabled/disabled
Basic FCT Entry:
1234567FCT CUSTFILE DSNAME=CICS.CUSTOMER.FILE ACCMETH=VSAM STATUS=ENABLED OPENTIME=FIRSTREF CLOSETIME=LASTREF STRNO=1
OPENTIME: When file opens (FIRSTREF, PREOPEN)
CLOSETIME: When file closes (LASTREF, IMMEDIATE)
STRNO: Number of strings (concurrent access)
RECOVERY: Recovery options
Advanced FCT Entry:
123456789FCT CUSTFILE DSNAME=CICS.CUSTOMER.FILE ACCMETH=VSAM STATUS=ENABLED OPENTIME=PREOPEN CLOSETIME=IMMEDIATE STRNO=5 RECOVERY=YES SHARED=YES
Performance Optimization:
Security & Recovery:
Control Interval (CI) and Control Area (CA) sizing significantly impact VSAM performance. Proper sizing reduces I/O operations, improves response time, and optimizes storage utilization.
Factors: Record size, access pattern, I/O efficiency
Common Sizes: 2KB, 4KB, 8KB, 16KB, 32KB
Guidelines: 50-80% CI utilization
Impact: I/O performance, storage efficiency
CI Sizing Example:
123456789* For 500-byte records with 80% utilization * CI Size = 500 bytes / 0.80 = 625 bytes * Round up to next power of 2: 1KB * Recommended CI size: 1KB * For 2KB records with 75% utilization * CI Size = 2048 bytes / 0.75 = 2730 bytes * Round up to next power of 2: 4KB * Recommended CI size: 4KB
Purpose: Storage allocation unit
Relationship: Multiple of CI size
Considerations: Growth, performance, storage
Guidelines: Balance efficiency and growth
CA Sizing Example:
1234567891011* For 4KB CI size * Common CA sizes: 16KB, 32KB, 64KB * 16KB = 4 CIs (good for small files) * 32KB = 8 CIs (balanced approach) * 64KB = 16 CIs (good for large files) * For 8KB CI size * Common CA sizes: 32KB, 64KB, 128KB * 32KB = 4 CIs * 64KB = 8 CIs * 128KB = 16 CIs
CI Size Optimization:
CA Size Optimization:
CICS provides comprehensive VSAM support through EXEC CICS commands. Understanding these operations and their performance characteristics is essential for effective VSAM integration.
READ: Retrieve records by key or position
WRITE: Add new records to file
REWRITE: Update existing records
DELETE: Remove records from file
VSAM Operations Example:
12345678910111213141516171819202122232425262728IDENTIFICATION DIVISION. PROGRAM-ID. VSAMOPS. ENVIRONMENT DIVISION. DATA DIVISION. WORKING-STORAGE SECTION. 01 WS-CUSTOMER-RECORD. 05 WS-CUST-ID PIC X(10). 05 WS-CUST-NAME PIC X(30). 05 WS-CUST-ADDR PIC X(50). PROCEDURE DIVISION. * Read customer record EXEC CICS READ FILE('CUSTFILE') INTO(WS-CUSTOMER-RECORD) RIDFLD(WS-CUST-ID) RESP(WS-RESPONSE) END-EXEC * Update customer address MOVE 'NEW ADDRESS' TO WS-CUST-ADDR * Rewrite updated record EXEC CICS REWRITE FILE('CUSTFILE') FROM(WS-CUSTOMER-RECORD) RESP(WS-RESPONSE) END-EXEC EXEC CICS RETURN END-EXEC.
STARTBR: Begin browse operation
READNEXT: Read next record
READPREV: Read previous record
ENDBR: End browse operation
Browse Example:
1234567891011121314151617181920212223242526272829303132333435IDENTIFICATION DIVISION. PROGRAM-ID. VSAMBROWSE. ENVIRONMENT DIVISION. DATA DIVISION. WORKING-STORAGE SECTION. 01 WS-CUSTOMER-RECORD. 05 WS-CUST-ID PIC X(10). 05 WS-CUST-NAME PIC X(30). PROCEDURE DIVISION. * Start browse from beginning EXEC CICS STARTBR FILE('CUSTFILE') RIDFLD(LOW-VALUES) END-EXEC * Read first 10 records PERFORM VARYING WS-COUNTER FROM 1 BY 1 UNTIL WS-COUNTER > 10 EXEC CICS READNEXT FILE('CUSTFILE') INTO(WS-CUSTOMER-RECORD) RIDFLD(WS-CUST-ID) RESP(WS-RESPONSE) END-EXEC IF WS-RESPONSE = DFHRESP(NORMAL) PERFORM PROCESS-CUSTOMER ELSE EXIT PERFORM END-IF END-PERFORM * End browse EXEC CICS ENDBR FILE('CUSTFILE') END-EXEC EXEC CICS RETURN END-EXEC.
Continuous monitoring and tuning of VSAM performance is essential for maintaining optimal application performance. Use CICS monitoring tools and VSAM statistics to identify bottlenecks.
CEMT: Monitor file status and performance
CMF: CICS Monitoring Facility
SMF Records: System Management Facility
Performance Analyzer: Detailed analysis
CEMT Commands:
12345678* Display file status CEMT INQUIRE FILE(CUSTFILE) * Display file statistics CEMT INQUIRE FILE(CUSTFILE) STATISTICS * Display all files CEMT INQUIRE FILE(*)
CI Splits: Performance impact indicator
Free Space: Storage efficiency measure
I/O Counts: Access pattern analysis
Response Times: Performance measurement
Key Metrics:
1234567* Monitor these VSAM statistics: * - CI splits (should be minimal) * - Free space utilization * - I/O operations per transaction * - Average response time * - Buffer hit ratios * - String utilization
Question 1:
What is the difference between CI and CA in VSAM?
Question 2:
When should you use PREOPEN vs FIRSTREF in FCT entries?
Question 3:
What are the main factors to consider when sizing VSAM CIs?