Symptoms of web application performance problems

• Long user response time
• Long server response time
• Memory leaks
• High CPU usage
• Too many open connections 
• Length queues for requests
• Too many table scans of database
• Database deadlocks
• Erroneous data returned
• HTTP errors
• Pages not available

Typical database problems

• Insufficient indexing : Tune database indexing to improve query processing
• Fragmented databases : Place table records into adjacent pages
• Out-of-date statistics :Degrade query optimizer performance
• Faulty application design : Excessive DB calls, excessive data requests

Typical Web Server problems

• Poor server design : Inefficient data or page caching
• Memory problems : Physical memory constraints
• High CPU usage : Usage >70% indicates problems

Typical app server problems

• Poor database tuning : Application server sending too many DB requests
• Poor cache management : Produces high CPU usage, disk access
• Poor session management :  Produces high CPU usage, disk access, Time-outs
• Poor security design : Excessive use of https protocol

Network problems

Potential sources of network problems:

• Firewall throughput
• Internet access throughput
• Load balancers, gateways, routers

Typical order of fixes

1. Improve current application design : Algorithms, caching, DB calls, memory use
2. Upgrade hardware : RAM, CPU, network bandwidth
3. Upgrade software infrastructure : OS, web server, database
4. Upgrade system architecture : Client-server to basic n-tier, basic n-tier to enterprise n-tier, software and hardware changes