Question

I have seen this show up several places in code, never with an explanation, just a cryptic comment above it (Declaration and execution included for an idea of context. It’s just a standard procedure of running a SqlCommand):

//SqlCommand cmd = new SqlCommand();
//cmd.ExecuteReader();
//Read off the results

//Cancel the command. This improves query time.
cmd.Cancel ();

Basically, after finishing a query, it goes back and cancels it, claiming some performance boost. I suppose you might get some memory back when it goes and frees up the XmlReader, but usually it’s about to go out of scope anyways.

I’ve never bothered with it before, but it’s finally showed up in some code I’m reviewing. Does canceling a SqlCommand after running it in the code actually somehow speed it up, or is this just some weird programmer superstition?

Answer 1

According to MSDN, this is correct.

The Close method fills in the values
for output parameters, return values
and RecordsAffected, increasing the
time that it takes to close a
SqlDataReader that was used to process
a large or complex query. When the
return values and the number of
records affected by a query are not
significant, the time that it takes to
close the SqlDataReader can be reduced
by calling the Cancel method of the
associated SqlCommand object before
calling the Close method.

Weird!