CODEWITHSUNDEEP
vb.net
James Stafford
James Stafford

Reputation: 1054

vb.net Formatting for high performance

I have recently noticed on my performance assist tool I use on Visual Studio 2013 any time I make a complex string

as a sample string:

"SELECT * from calls where randid = '" & randid & "'"

it will instead recommend using string format

String.Format("SELECT * from calls where randid = '{0}'", randid)

same with using value initializers instead of

        Dim cb As New MySqlConnectionStringBuilder
        cb.Database = dbfile
        cb.Server = dbserver
        cb.UserID = dbuser
        cb.Password = dbpassw

use

Dim cb As New MySqlConnectionStringBuilder() With {.Database = dbfile, .Server = dbserver, .UserID = dbuser, .Password = dbpassw}

Do these formats actually improve the performance of an application or is it recommending these for aesthetics?

Upvotes: 1

Views: 99

Answers (2)

Steve
Steve

Reputation: 216348

Out of curiosity (I am absolutely sure that mini-optimizations are devilish) I have tested the difference with this code using LinqPad:

Sub Main
    Dim  test = "999"
    Dim sw = new Stopwatch()
    sw.Start()
    for i = 0 to 100000
        Dim s = "SELECT * FROM TABLE WHERE FIELD = '" + test + "'"
    Next
    sw.Stop()
    sw.Elapsed.Dump("Concat")

    sw = new Stopwatch()
    sw.Start()
    for i = 0 to 100000
        Dim  s = string.Format("SELECT * FROM TABLE WHERE FIELD = '{0}'", test)
    Next
    sw.Stop()
    sw.Elapsed.Dump("Format")
End Sub

with these results:

Concat 
00:00:00.0101903 

Format 
00:00:00.0365234

The output changes noticeably if we use an integer for the test variable because now the concatenation should use ToString()

Dim test = 999

Concat 
00:00:00.0198107 

Format 
00:00:00.0485193

So, for whatever reason your tool suggest to use the string.Format approach it is not to get better performance.

Upvotes: 1

MarcinJuraszek
MarcinJuraszek

Reputation: 125650

In the first one compiler will generate String.Concat method call for your string concatenation:

return "test" + value + "test";

it translated into

IL_0000: ldstr "test"
IL_0005: ldarg.0
IL_0006: box [mscorlib]System.Int32
IL_000b: ldstr "test"
IL_0010: call string [mscorlib]System.String::Concat(object, object, object)
IL_0015: ret

Both String.Concat and String.Format will cause boxing (I assumed randid is an int). You should call ToString() on it anyway to make it better.

The second one is a lay. Compiler will generate properties assignments anyway, so 

Dim cb As New MySqlConnectionStringBuilder() With {.Database = dbfile, .Server = dbserver, .UserID = dbuser, .Password = dbpassw}

is transformed into 

Dim cb As New MySqlConnectionStringBuilder
cb.Database = dbfile
cb.Server = dbserver
cb.UserID = dbuser
cb.Password = dbpassw

by compiler.

Upvotes: 1

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