Job Class2

Key Characteristics

• * Single-character designation (A-Z, 0-9) - 36 possible classes * Controls job selection from input queue * Influences scheduling priority and execution order * Determines initiator assignment and availability * Groups similar workload types for management * Specified on JOB statement CLASS parameter * Can be changed by operators or automation
• Class Usage Patterns:
• *Production Classes (A-D):* * Critical business processing jobs * Highest priority execution * Guaranteed resources * Restricted to production datasets * Monitored service levels
• *Development/Test Classes (T-Z):* * Application development and testing * Lower priority than production * Limited resource consumption * Access to test datasets * Flexible scheduling
• *Resource-Based Classes:* * Short Jobs (Q, S): < 5 minutes execution * Medium Jobs (M): 5-30 minutes execution * Long-Running (L, X): > 30 minutes execution * High CPU (H): Compute-intensive processing * High I/O (I): Data-intensive operations
• *Special Purpose Classes:* * Overnight Batch (N): Night processing window * Weekend Processing (W): End-of-week jobs * Month-End (E): Financial close activities * Ad-hoc/Emergency (Z): Urgent requests
• Class Assignment Factors:
• *Job Characteristics:* * Estimated run time and duration * CPU requirements and intensity * Memory (region) requirements * DASD space needs * Tape drive requirements * Print volume expectations
• *Business Requirements:* * Business criticality and priority * Service level agreements (SLAs) * Time-of-day restrictions * Processing window constraints * Dependencies on other jobs
• *Operational Considerations:* * System capacity at run time * Resource contention management * Load balancing requirements * Backup and recovery windows
• JCL Specification
• `jcl //JOBNAME JOB (ACCT),'DESCRIPTION', // CLASS=A, ← Production class // MSGCLASS=X, ← Output class // MSGLEVEL=(1,1)
• //TESTJOB JOB (DEVACCT),'TEST RUN', // CLASS=T, ← Test class // TIME=(,5), ← 5 minute limit // REGION=4M
• //LONGJOB JOB (BATCHACCT),'MONTH END', // CLASS=L, ← Long-running class // TIME=1440, ← 24 hour limit // NOTIFY=&SYSUID `
• Initiator Configuration:
• *Initiator Setup:* * Each initiator assigned to one or more classes * Multiple initiators can serve same class * Class-based selection priority * Dynamic initiator class changes * Maximum concurrent jobs per class
• Example Configuration:

  Initiator 1: Classes A,B,C (Production - Priority 15)
  Initiator 2: Classes A,B,C (Production - Priority 15)
  Initiator 3: Classes D,M (Medium - Priority 10)
  Initiator 4: Classes L,X (Long-running - Priority 5)
  Initiator 5: Classes T,Z (Test/Dev - Priority 3)

• Selection Algorithm:
  * Higher class priority selected first * Within class: submission time order * Job priority parameter override * Affinity and dependency considerations * Resource availability requirements
• Class Management:
• Static Assignment:
  * Defined in JCL CLASS parameter * Set by application standards * Based on job categories * Documented in operations procedures
• Dynamic Class Changes:
  * Operator commands: $T J=jobname,Q=class * Automated class routing * WLM-based adjustments * Time-of-day reclassification * Emergency priority escalation
• Monitoring and Tuning:
  * Class utilization reports * Queue depth by class * Service level attainment * Resource consumption patterns * Initiator efficiency analysis
• Integration with WLM:
• Service Classes:
  * Job class maps to WLM service class * Performance goals by class * Resource group assignment * Velocity goals and importance * Multi-level priority structure
• Policy Management:
  * Different policies by time period * Business importance mapping * Resource distribution goals * Response time objectives
• Alphabetic Scheme:

  A = Critical Production (Priority 15)
  B = Standard Production (Priority 12)
  C = Medium Priority (Priority 10)
  D = Development/Test (Priority 8)
  E = Long-Running Batch (Priority 6)
  F-Z = Special purposes

• Numeric/Mixed Scheme:

  0-3 = Production levels
  4-6 = Development tiers
  7-9 = Special processing
  A-Z = Application-specific

• Class-Related JES2 Commands:
• Display Class Information:

  $DJQ,Q=A              Display jobs in class A
  $DI                   Display initiator status
  $DJOBQ               Display all job queues

• Modify Class Assignments:

  $T J=jobname,Q=A     Change job to class A
  $T I=initid,CL=ABC   Modify initiator classes
  $P I=initid          Stop initiator
  $S I=initid,CL=T     Start initiator for class T

• Class Priority Changes:

  $T J=jobname,P=15    Change job priority

• Best Practices:
• Class Design:
  * Limit number of classes (8-12 typical) * Clear naming conventions * Documented class purposes * Balance between granularity and simplicity * Regular review and optimization
• Operations:
  * Monitor class queue depths * Balance initiator assignments * Document emergency procedures * Establish class change authorities * Track service level by class
• Application Standards:
  * Standard class assignments by application * Developer guidelines for class selection * Review process for class changes * Documentation in run books
• Performance Considerations:
• Queue Management:
  * Avoid class starvation * Balance short and long jobs * Prevent queue backups * Monitor hold/wait conditions
• Resource Optimization:
  * Match initiators to workload * Consider time-of-day patterns * Adjust for month-end processing * Plan for peak periods
• Capacity Planning:
  * Analyze class trends * Forecast growth by class * Plan initiator capacity * Consider specialty engines (zIIP, zAAP)
• Troubleshooting:
• * Jobs stuck in queue - check initiator availability * Wrong class assignment - verify JCL standards * Class starvation - adjust initiator mix * Priority inversion - review class priorities * Resource contention - analyze concurrent jobs
• Diagnostic Commands:

  $DJOBQ               Review all queues
  $DI                  Check initiator status
  $DA                  Display active jobs
  $DJ,Q=class          Focus on specific class

Use Cases

• Production Workload Segregation:
  * Separate critical from non-critical jobs * Ensure production processing windows * Prevent test jobs from impacting production * Guarantee resources for business-critical work
• Resource Management:
  * Control long-running job impact * Balance I/O and CPU intensive work * Manage tape drive allocation * Prevent system resource exhaustion
• Business Priority Implementation:
  * Express business importance through class * Different service levels by class * Time-critical processing prioritization * Customer-specific processing classes
• Operational Control:
  * Enable/disable classes for maintenance * Emergency job processing * Scheduled downtime management * Disaster recovery prioritization
• Capacity Planning:
  * Workload classification for analysis * Growth trending by job category * Resource forecasting by class * Chargeback by processing type
• See Also:
  * Job - Unit of work assigned to class * Job Step - Individual program execution within job * Initiator - Executes jobs from class queues * WLM (Workload Manager) - Dynamic resource management * JES2/JES3 - Job entry subsystems managing classes * JCL (Job Control Language) - Language specifying class * Batch Processing - Primary context for job classes

Related Concepts