ActiveLogFile performance Article

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ActiveLogFile performance

Performance notes and comparison with FileSystemObject and its use to do log files in ASP.

      Maybe, you need some logging for your asp application. You want to log current time and some other values to the log file and you need to have daily logs. This page contains some small info about performance and locking problems in ASP.
      1. The first solution you can use is Scripting.FileSystemObject :
<%
....

DoLogFS1 "Some log value"

 
Function DoLogFS1(LogLine)
  Dim OutStream, FileName
  Const LogSeparator = " "
  FileName = "D:\LogFiles\fs1" & Right("0" & _
    Year(Now), 2) & Right("0" & Month(Now), 2) & Right("0" & Day(Now), 2) & ".Log"

  Set OutStream = CreateObject("Scripting.FileSystemObject").OpenTextFile _
    (FileName, 8, True)
  OutStream.WriteLine Now() & LogSeparator & LogLine
End Function

%>
      Simple function. But it takes most of the time to create filesystem object. 
      2. You can put the FileSystemObject to global.asa and modify your function:
<Object RunAt=Server ID=FS ProgID=Scripting.FileSystemObject Scope=Application></Object>
and use the FileSystemObject i your ASP page:
<%
....

DoLogFS2 "Some log value"
 
Function DoLogFS2(LogLine)
  Dim OutStream, FileName
  Const LogSeparator = " "
  FileName = "D:\LogFiles\fs2" & _
    Right("0" & Year(Now), 2) & Right("0" & Month(Now), 2) & Right("0" & Day(Now), 2) & ".Log"

  Set OutStream = FS.OpenTextFile (FileName, 8, True)
  OutStream.WriteLine Now() & LogSeparator & LogLine
End Function
%>

      This function takes 4 times less time than version 1. But this function takes most of the time to open log file for append.
      3. We can do last optimalization - store the file stream in application :
<Object RunAt=Server ID=FS ProgID=Scripting.FileSystemObject Scope=Application></Object>
<SCRIPT LANGUAGE=VBScript RUNAT=Server>

Sub Application_OnStart
  Dim OutStream, FileName
  FileName = "D:\LogFiles\fs2" & _
Right("0" & Year(Now), 2) & Right("0" & Month(Now), 2) & Right("0" & Day(Now), 2) & ".Log" Set OutStream = FS.OpenTextFile (FileName, 8, True) Set Application("OutStream") = OutStream End Sub </SCRIPT>
and use the stream i an ASP page:
<%
  ....

DoLogFS3 "Some log value"

Function DoLogFS3(LogLine)
  Const LogSeparator = " "
  Application("OutStream").WriteLine Now() & LogSeparator & LogLine
End Function

%>
      The codes number 1. and 2. have also also another problem - simultaneous requests. When the page is used by many browsers, open of the log file for append may fail. For example, if you do 10 000 requests from 10 browsers to the page, you wil have 9542 records in your log file (or similar number). Some log records will be lost because first call of OpenTextFile for append locks the log file and second call from another request will fail.
      The code number 3 solves the problem, but you have another problem - now you have no daily logs, but only one log with date of start of ASP application.

      4. We can compare performance of a best solution for the problem, LogFile class. The class solves problems with daily file name, simultaneous requests and many other problems and tasks. Global.asa:
<Object RunAt=Server ID=LogFile ProgID=ScriptUtils.LogFile Scope=Application></Object>
<SCRIPT LANGUAGE=VBScript RUNAT=Server>

Sub Application_OnStart
  LogFile.TemplateFileName = "D:\Log\LG%y%m%d.Log"
End Sub

</SCRIPT>
ASP page:
<%
  ....

  LogFile.Log "Some log value" 
%> 

      Next table contains a short performance comparison of the four source codes. The times was from PII Celeron/500MHz.

 Code number  Microsecond
 1. Simple FileSystemObject   3 800 
 2. FileSystemObject in Application   950 
 3. TextStream in Application   150 
 4. LogFile class   60 

 
      5. But you want to log more values than only one.
  Dim vCurr, vDbl, vStr, vDate, vEmpty

  vCurr = CCur (256.235)
  vDbl  = CDbl (23215.132154)
  vStr  = "Some string value"
  vDate = Now

      We can use FileSystemObject and code no. 3 or LogFile class:

  DoLogFS4 vStr & LogSeparator & vCurr & LogSeparator & _
    vDbl & LogSeparator & vDate & LogSeparator & vEmpty

  or
 
  LogFile.Log vStr, vCurr, vDbl, vDate, vEmpty
 Code  Microsecond
 FileSystemObject   230 
 LogFile class   115 

      You can see that LogFile class has at least 2 times better performance than text Stream from FileSystemObject. And the class solves many other problems and work with logging ...

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