AS400 Is Not the Bottleneck – The Workflow Logic Often Is

Many AS400-based systems are still performing well — until they’re not. The degradation is rarely due to hardware or the OS, but rather due to operational inefficiencies baked into job schedules, CL program structures, file usage, and data handling.

The issue isn’t that AS400 is outdated — it’s that its logic has been rigidly layered over time without rethinking execution paths, dependencies, or modularity. Now, what are the bottlenecks? Is this something that expert AS400 services can solve? Let’s find out.

Bottleneck #1 – Poorly Sequenced Job Scheduling

The Root Cause

As business needs expanded, many AS400 systems accumulated new jobs that were inserted into existing chains, often in a serial fashion. Over time, this created massive, inflexible batch runs — usually overnight — with:

• Tight dependencies between jobs
• Poor queue prioritization
• Manual checkpoints

The Fix

• Use tools like WRKJOBSCDE and IBM i Navigator to visualize all scheduled jobs
• Reevaluate sequences — identify which jobs can run in parallel
• Use conditional job triggering via SBMJOB, DLYJOB, and MONMSG
• Group jobs into logical subsystems and route them to different job queues to manage load

Bottleneck #2 – Overreliance on Physical Files for Intermediate Storage

The Root Cause

Many workflows rely on intermediate physical files for data transformation and staging. This leads to:

• High disk I/O
• File locks during critical operations
• Performance degradation during copy or reorganize operations

The Fix

• Replace physical staging files with logical file views
• Use in-memory processing techniques wherever feasible
• Implement DB2 Common Table Expressions (CTEs) to eliminate temporary file usage
• Archive unused or redundant files to reduce contention

Bottleneck #3 – Inefficient Data Transfer Between Systems

The Root Cause

Traditional AS400 setups often rely on FTP scripts or manual data exports using CPYTOIMPF, CPYFRMIMPF, or spool files. These methods:

• Transfer entire files even for minor updates
• Increase processing time
• Are error-prone and hard to monitor

The Fix

• Use data queues or message queues for event-driven data exchange
• Filter exports using SQL queries to send only deltas
• Replace FTP with REST APIs or JDBC connections for dynamic access
• Automate exports using timestamp-based filtering and scheduling

Bottleneck #4 – Green Screen User Tasks Embedded in Critical Processes

The Root Cause

Some CL programs expect user interaction mid-run — a leftover from menu-driven logic. These manual steps:

• Halt batch jobs until a user responds
• Cause unpredictable wait times
• Increase chances of human error

The Fix

• Eliminate interactive prompts in CL using program messages (SNDPGMMSG)
• Replace UI dependencies with data queue triggers or automated decisions
• Use RPA to simulate user input for non-removable green screen interfaces

Bottleneck #5 – Inflexible CL and RPG Program Design

The Root Cause

Legacy code often includes hardcoded file paths, program calls, and date logic. These designs:

• Are hard to maintain
• Don’t allow for dynamic input
• Force rigid processing paths

The Fix

• Convert fixed-format RPG to free-form RPGLE for better readability and modularity
• Use parameters and service programs for reusable logic
• Introduce modular design using procedure calls
• Document and decouple program chains

Bottleneck #6 – No Centralized Monitoring or Logging

The Root Cause

Without centralized error reporting, issues often surface only after job failures. Most organizations rely on:

• Manual log checks (DSPJOBLOG, DSPLOG)
• Inconsistent error trapping
• No real-time visibility into job health

The Fix

• Route messages to QSYSOPR queue and trap MSGW status
• Implement alerting systems using SNMP or Syslog integrations
• Automate job summary emails using WRKACTJOB snapshots
• Use IBM i Services (SQL interfaces) to create dashboards

Modernizing Without Rewriting – Your Practical Playbook

Where to Start

Begin by targeting areas with the highest impact:

• Long-running nightly/weekly jobs
• Manual checkpoints
• File copy-heavy processes
• Frequently failing programs

Tools That Help Without Full Modernization

• IBM i Navigator – Job scheduling & performance insights
• Performance Explorer (PEX) – Analyze CPU, disk, and job behaviors
• DB2 Web Query – Build modern reports from legacy data
• SQL Services (ACS) – Direct querying and automation

Summary: Fix the Logic, Not the Platform

Most IBM i systems are slowed down not by the hardware or OS, but by inefficient workflows that have compounded over time. Before considering a complete rewrite, look under the hood:

• Are jobs sequenced properly?
• Are intermediate files adding unnecessary load?
• Is user input stalling automation?
• Is your system silently waiting for something you don’t need anymore?

The platform is rock solid — you just need to modernize the logic layer to match today’s business demands.

What’s Next? Start With a System Workflow Audit

Before embarking on large-scale modernization, conduct a workflow audit:

• What runs
• When it runs
• Who triggers it
• How data flows

This audit will uncover optimization opportunities that can deliver outsized performance and efficiency benefits — all without rewriting core business logic.