Monday, 8 September 2008

Top 10 Tips for improving ASP performance

Top 10 Tips For Speeding up ASP Classic Sites

1. Look for nested loops and replace them with SQL stored procs. Its surprising how many times I have looked at sites that when outputting product hierarchies or menus on those old catalogue sites use nested loops to build up the content. Its usually people who got into programming on the web side with little or no SQL knowledge that was then learnt later only as and when they required somewhere to persist the data. Replace nested loops with SQL Stacks (see BOL) or in 2005 a recursive CTE. From tests I have found the Stack to perform slightly faster than the CTE but both will outperform nested loops. The data will most likely be in an adjacency table anyway so its just the method of outputting it. I remember replacing one such beast of nested loops with a stored procedure stack and it increased performance by a factor of 20.

2. Re-use those objects. Do you have helper functions that carry out regular expressions or file system object actions that instantiate the object within the function. If you call these functions
more than once on a page you are creating an unneccesary overhead. Have a global include file where you declare some often used variables. Then the first time you call the function if it doesn't exist initialise it otherwise use the existing object pointer. Then destroy them all in your global footer.

3. Simplify any complex regular expressions by breaking them down into multiple parts. I have had problems with badly written regular expressions causing CPU on our webserver to max at 100%. On our quad it would jump to 25%, four hits at the same time and 100% and then no other pages would load. Also complex expressions that do lots of lookbacks will cause overhead and the longer the string you are testing against the more overhead you will get. Remember VBs Regular Expression engine is not as good as some others so its better to break those long complex expressions up into smaller tests if possible.

4. String concatenation. In ASP.NET you have the string builder class but in ASP classic you should create your own using Arrays to store the string and then do a JOIN at the end to return it. Doing something like the following

For x = 1 to 100
strNew = strNew & strOtherString
Next
May work okay if the size of the string in strOtherString is small and you have few iterations but
once those strings get larger the amount of memory used to copy the existing string and then add it to the new one will grow exponentially.

5. Try to redim arrays as few times as possible especially if you are doing a Preserve. Its always best to dim to the exact size before hand but if you don't know how big your array will be then
dim it to a large number first and then use a counter to hold how many elements you actually add. Then at the end you redim preserve once back down to the number of elements you actually used. This uses a lot less memory than having to redim preserve on each addition to the array.

6. Use stored procedures for complex SQL and try to reduce database calls by calling multiple SQL together and then using NextRecordset() to move to the next set of records when you need to. Using stored procedures will also reduce network traffic as its much easier to connect to the DB once and pass through the names of 3 stored procedures than connect 3 times passing through the X lines of SELECT statements that each recordset requires.
strSQL = "EXEC dbo.usp_asp_get_records1; usp_asp_get_recorddetails; usp_asp_get_country_list;"

Set objRS = objConnection.Execute(strSQL)

If not(objRS.BOF AND objRS.EOF) Then
arrRecords = objRS.GetRows()
Set objRS = objRS.NextRecordset()
End If
If not(objRS.BOF AND objRS.EOF) Then
arrRecordDetails = objRS.GetRows()
Set objRS = objRS.NextRecordset()
End If
If not(objRS.BOF AND objRS.EOF) Then
arrCountryList = objRS.GetRows()
End If
7. Make sure that you don't put multiple conditions in IF statements. ASP doesn't support short circuiting which means it evaluates every condition in an IF statement even if the first one
is false. So rewrite code such as:

If intCount = 1 AND strName = "CBE" AND strDataType = "R" Then
'Do something
End If

If intCount = 1 Then
If strName = "CBE" Then
If strDataType = "R" Then
'Do something
End If
End If
End If
8. Also make sure you evalutate conditions in the correct order if you are checking a value for True and False then you don't waste an extra check when you can just change the order of the conditions.

If Not(bVal) Then
Response.Write("NO")
Else
Respone.Write("YES")
End If
Should obviously be

If (bVal) Then
Response.Write("YES")
Else
Respone.Write("NO")
End If
8. Cache as much data as possible if it doesn't change frequently. If you have lists that come from a database but never change or very infrequently change then you could either store them in memory and reload every so often or write the array to a file and then use that static array and only re-create the file when the data changes. I always add an admin only function into my sites that on the press of a button will reload everything I need to into files and cache. This prevents un-required database lookups.

9. Pages that contain database content that's added through the website that only changes when the user saves that content can be created to static HTML files if possible. Rather than rebuilding the page from the DB each time someone views it you can use the static version. Only rebuild the page when the user updates the content. For example a lot of CMS systems store the content within the DB but create a static version of the page for quick loading.

10. Encode and format content on the way into the database not each time its outputted to be displayed. Its more cost efficent to do something once on the way in that hundreds of times on the way out.

These are just a few of the things I have found out that can be very beneficial in speeding up a classic ASP site on the web side of things. As well as any performance tweaks that can be done application side you should take a look at the database to make sure thats performing as well as possible. If your site is data driven then a lot of the performance will be related to how quick you can build those recordsets up and deliver them to the client.

No comments:

Latest Cheap Amazon Goods