In the world of application management, performance issues are inevitable. While you might have a solid methodology for establishing and improving application performance, emergencies demand a different approach. When a system suddenly shifts from being reliable and predictable to sluggish and unresponsive, immediate action is required to restore normal service.
Responding to Performance Emergencies
When faced with a performance emergency, the first priority is to quickly identify what has changed and take corrective action. Here’s how to navigate through these high-pressure situations effectively:
1. Survey the Problem and Gather Symptoms
Begin by surveying the performance problem to understand the symptoms:
- User Feedback: Get insights from users about how the system is underperforming. Determine whether the issue is related to throughput, response time, or another metric.
- Identify Changes: Ask the critical question, "What has changed since the system last performed well?" While this might seem straightforward, getting accurate answers during an escalated situation can be challenging. Look for objective reference points, such as statistics or log files, to compare the system's performance before and after the issue arose.
- Use Diagnostic Tools: Leverage automatic tuning features and tools like Oracle Enterprise Manager Cloud Control to diagnose the problem. These tools can help identify top SQL queries and sessions that may be contributing to the performance issue.
2. Conduct a Sanity Check on Hardware Utilization
Next, check the hardware utilization across all components of the application system:
CPU, Disk, Memory, and Network Performance: Determine where the highest CPU utilization is occurring and assess disk, memory, and network performance. This quick analysis will help you identify which tier of the system—application, database, or another component—is causing the problem.
Application vs. Database Server: If the issue appears to be with the application, shift your focus to debugging the application. If the problem lies within the database server, proceed with a more detailed analysis of the database.
3. Analyze Database Server Constraints
If the database server is the bottleneck, identify whether it’s constrained by CPU usage or wait events:
- CPU Constraints: If the database server is CPU-constrained, investigate sessions consuming high CPU resources. Use views like V$SESS_TIME_MODEL for database CPU usage and V$SESSTAT and V$SQLSTATS to identify sessions or statements with high buffer gets. Look for execution plan changes that may be causing suboptimal SQL execution, incorrect initialization parameters, or algorithmic issues due to recent code changes or upgrades.
- Wait Events: If the database is experiencing wait events, follow the wait events listed in V$SESSION_WAIT to diagnose what’s causing the delays. The V$ACTIVE_SESSION_HISTORY view provides a sampled history of session activity, which is useful for post-incident analysis. If there’s significant contention, especially for resources like the library cache latch, you may need to rely on historical data to understand the root cause.
4. Apply Emergency Actions
To stabilize the system, you may need to take drastic actions:
- Restrict Workload or Take Components Offline: In some cases, it might be necessary to restrict the workload on the system or take parts of the application offline to reduce the load. This could involve restarting the system or terminating processes that are consuming excessive resources.
- Service Level Implications: Be aware that these emergency actions could have service level implications, such as temporary outages or reduced functionality for users.
5. Validate System Stability
After applying emergency actions, it’s crucial to ensure the system is stable:
- Collect Reference Statistics: Once the system is stabilized, gather a new set of reference statistics for the database. This will help in future performance analysis and in ensuring that the system remains stable.
- Long-Term Performance Improvement: While the immediate issue may be resolved, the work isn’t over. Follow a rigorous performance improvement method to fully restore functionality and user access. This might involve significant reengineering of the application or other components.
Conclusion
Performance emergencies require a swift and methodical approach to bring a system back to normal operation. By following these steps, you can quickly diagnose the problem, apply necessary fixes, and stabilize the system. Remember, keeping detailed notes throughout the process is essential, as it provides valuable insights for both immediate resolution and future prevention. Just like a doctor documenting patient records, your notes will serve as a critical reference for ongoing performance management.
Read more :
DBA's Guide to Troubleshooting Database/Query Performance Problems
&
Addressing Client-Reported Slowness: A DBA's Guide
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