How can I determine why a Visualforce page is slow?

Question

The page in question takes a full minute to load. But only for one client, and I only have access to that clients sandbox.

If I was developing normally, I would use the Developer's Console and logs to determine why a Visualforce page loads very slowly. However the slowness only occurs for one client. They are a very large company and have thousands of users and fields and objects etc on Salesforce. I tested a few suspicious SOQL queries on the page, but found they all completed within .5 seconds.

I am at a loss as to how I can find the cause of the problem. I tried to get my developer account 'big' enough to recreate the issue but I could only create a max of 200 users and only 5,000 roles which was not enough to cause the slowness.

My current plan of action would be to make a few educated guesses about what the problem could be, make those changes, then get the client to install that new package in their sandbox. However, since they are large, they are slow :) and it could take weeks to install each package. I would like to be relatively certain I have a good idea what the problem is before I try random fixes that will take a long time to test.

Any ideas?

Answer 1

My organization had a similar issue with Visualforce and Apex code that was developed for us by a consultant. The code ran reasonable quickly in a full data sandbox. In our production instance, the same code often timed out on the query. The consultant, a Salesforce MVP, worked directly with Salesforce support. The end result was that the queries used were changed significantly based on feedback from Salesforce support.

You could start by looking at the query optimization cheat sheet to see if anything suggested there looks likely to help. There's also this page that talks about working with very large SOQL queries. It's hard to get more specific without more detail. If you're uncertain where the problem lies, start by using log files and added "system.debug" statements to narrow down the code causing the delay.

One thing we learned was that Salesforce gives no performance guarantees with respect to how fast your code runs in a sandbox versus how fast it runs in production.

Note: the time-out issues were experienced by users who had access to all the organization's data. Users with more restricted access generally had no trouble.