Performance Sin - Chatty Database Access And Loops (Plus Another Free Performance Tool)
Chatty database access is the surefire way for slow performance caused by resources starvation that might even lead to denial of service. Following is a real world case.
Customer
Service Unavailable message is consistently observed when there are more than 150 users access the web site. We think IIS cannot handle more than 150 users. What would you suggest?
Support
Let's see what "Service Unavailable" means. "IIS cannot start any new worker processes because of limited system resources...". Let's see the code.
The code
The code was calling on DB Access function that was put inside for loop that was called inside event handler. The event handler was called on each GridVew's row creation. Meaning, DB access in nested loop. In case of small GridVew of 10 rows and 10 cells the database would be accessed 100 times for each request. 150 concurrent users would create significant load of 15,000 connections:
SQL Server Profiler
After running SQL Server profiler it became clear that database access should be significantly improved. Following is the number of SQL Commands performed as a result of single request:
Conclusion
For improved performance avoid chatty data base access. Apply caching techniques instead.
More free performance tools
If you use SQL Server 2005 Express which does not come with built-in profiler you might find useful the following free tool:
Profiler for Microsoft SQL Server 2005 Express Edition
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