What causes a page to render slow?

Question

I am puzzled. I looked at the trace of a pagecall that was "slow" to load according to my boss, causing the page to partially load, and then "jump" to the memorized scroll-place on a postback.

I found out eventually, using my trace, that my whole loading, from Begin PreInit to End Render, took 1.94 seconds, 1.5 of which are spent between Begin PreRender and End PreRender.

Any idea on what could cause that? The next biggest loadtime is 0.14 seconds, for End PreRenderComplete.

Could the problem originate from my queries to SQL Server, or a too vast quantity of controls on the page, even though most are "hidden"?

[edit:]It seems that my page load is very long when I show a certain form. My total render size is of 91537 bytes, 44483 of which are dedicated to that specific form. My viewstate seems kindof enormous. Also: Can a 404 to a JS file cause that kind of lag on load?

[update:] So I found the longest-running query, and it seems that even though it DOES seem quite chunky, it has ended running long before the page is even loaded. As added information: I am using quite a bit of SqlDataSources troughout the controls, to fill my dropdownlists and other interesting stuff of the like. Is that cluttering my app?

Answer 1

In order to identify the cause of a bottleneck you really ought to profile your code with a tool like ANTS Profiler or something similar.

A profiler will allow you to pinpoint the problem area by showing you which lines of code are slower than others.

Answer 2

In my experience (same problem as you), it's 90% a SQL issue.

Put some Stopwatch(es) around the query you are calling to find out which query is running slow.

Rendering asp.net control can't take so long....

Answer 3

I would use YSlow to determine if its from something on the client side or server side. We sometimes add timers to some queries then output the time to execute in an html comment... of course removing them when the testing is complete.

Does the page call anything hosted on an external site?

Answer 4

Your best bet is to use the Perfomance Wizard in Visual Studio and look at the Call Tree for your page. It will give you more details into the exact performance bottleneck.

I have seen this type of performance when there are too many complex controls declared on the page. Although it could easily be SQL related as well. To know for certain you need to look at the Call Tree and find out what the most expensive call is.

Answer 5

Of course, if it is sql-related, as many people have noted, "sql server profiler" is the tool to use (given that you're running mssql). mysql has "jetprofiler" (.com) which i haven't tried. once you've found the slow query, it's not rarely an indexing issue.

Answer 6

Check this out...

http://www.dotnetscraps.com/dotnetscraps/post/How-to-troubleshoot-issues-with-Page-Rendering-in-ASPNET.aspx