Here’s a fun little .Net speed optimization I found out today:
(In both of these “Reader” is a DataReader which I’m using to loop through a set of database records.)
dim myValue as string While Reader.Read() Try myValue = Reader("FieldWhichMayNotExist") Catch myValue = "This is a default value" End Try end While
And here’s Code #2:
dim myValue as string dim fieldExists as Boolean = FigureOutIfFieldExists(Reader, "FieldWhichMayNotExist") While Reader.Read() if fieldExists then myValue = Reader("FieldWhichMayNotExist") else myValue = "This is a default value" end if End While
So, what’s the big difference? The first one traps for the field not existing and inserts a default value if so; and the second one wastes a bunch of time going through a routine to see if the field exists, then loops through and uses the result of that first scan to use either the field value or the default value accordingly.
You might think that the two would run in similar amounts of time–or maybe even Code #1 would be a little faster, since it didn’t waste a few precious milliseconds scanning to see if the field exists.
But here’s the shocker: Code sample #2 runs about 20 times faster than code sample #1, since it doesn’t need to deal with the whole .Net exception architecture. In the case of the actual code upon which this was based, it meant the difference between being able to insert 630,000 records in around 100 seconds, vs. more than an hour.
Exception handling: it’s more expensive than you think–particularly inside loops. Prevention in this case was worth 20 times more than a cure.