Troubleshooting slow jobs on IBM i (AS400) requires a systematic approach. Here's a breakdown of common causes and how to investigate them:
1. Identify the Slow Job
- WRKACTJOB: Use the
WRKACTJOB command to display active jobs. Look for jobs that have been running for an unusually long time or have a high CPU percentage.
- Job Logs: Check the job log of the suspected job for any error messages, long-running SQL queries, or other clues about the cause of the slowdown.
2. Common Causes and Solutions
-
CPU Bottleneck:
- Cause: The job might be CPU-intensive, and the system's CPU might be overloaded.
- Investigation:
- Check CPU utilization using
WRKACTJOB or performance monitoring tools.
- Identify other CPU-intensive jobs that might be competing for resources.
- Solutions:
- Increase the job's priority if it's critical.
- Optimize the job's code to reduce CPU usage (e.g., improve algorithms, reduce unnecessary calculations).
- If the system is generally overloaded, consider upgrading the CPU or adding more processing power.
-
Memory Bottleneck:
- Cause: The job might require more memory than is available, leading to excessive paging and poor performance.
- Investigation:
- Monitor memory usage and paging activity using performance monitoring tools.
- Check the job's memory pool to see if it's experiencing high faulting rates.
- Solutions:
- Increase the amount of memory allocated to the job's memory pool.
- Reduce the memory demands of the job (e.g., process data in smaller chunks).
- If the system is generally low on memory, consider adding more RAM.
-
I/O Bottleneck:
- Cause: The job might be waiting for data to be read from or written to disk, and disk I/O might be slow.
- Investigation:
- Monitor disk I/O activity using performance monitoring tools.
- Check for disk contention or slow disk drives.
- Solutions:
- Optimize database queries (e.g., use indexes effectively).
- Reduce the amount of data being read or written.
- Consider upgrading to faster disk drives or using RAID to improve disk performance.
-
Lock Contention:
- Cause: The job might be waiting for a lock on a file or database record that is held by another job.
- Investigation:
- Use the
DSPRCDLCK command to display record locks and identify which job is holding the lock.
- Solutions:
- If possible, reschedule jobs to avoid lock contention.
- Optimize application logic to reduce the duration of locks.
-
Network Bottleneck:
- Cause: If the job involves network communication, network latency or bandwidth limitations can cause slowdowns.
- Investigation:
- Monitor network traffic and identify any network congestion.
- Check for network errors or connectivity issues.
- Solutions:
- Upgrade network infrastructure or increase bandwidth.
- Optimize network communication protocols.
-
Database Issues:
- Cause: Slow SQL queries, missing indexes, or database configuration issues can affect job performance.
- Investigation:
- Analyze SQL queries used by the job using tools like Visual Explain.
- Check for missing or inefficient indexes.
- Review database configuration settings.
- Solutions:
- Optimize SQL queries (e.g., add indexes, rewrite queries).
- Tune database parameters.
-
Software Issues:
- Cause: Bugs in the application code or inefficient algorithms can lead to slow performance.
- Investigation:
- Review the application code for potential performance bottlenecks.
- Use debugging tools to trace the execution of the job.
- Solutions:
- Fix bugs in the code.
- Optimize algorithms and data structures.
3. Performance Monitoring Tools
- Performance Monitor: Use the Performance Monitor (part of IBM Navigator for i) to collect and analyze performance data. This tool can help you identify bottlenecks and track performance trends.
- Collection Services: Enable Collection Services to gather detailed performance data that can be used for in-depth analysis.
4. Other Tips
- Check for System Errors: Review system logs for any errors that might be affecting job performance.
- Consider System Values: Some system values can influence job scheduling and resource allocation. Review system values related to performance.
- Update the System: Ensure the system is running the latest PTFs (Program Temporary Fixes) to address any known performance issues.
Troubleshooting slow jobs often involves a process of elimination. Start by identifying the job, then systematically investigate potential causes, using the tools and techniques described above. Remember to document your findings and any changes you make to the system or application.
