This article was previously published under Q319998
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SYMPTOMS
When you retrieve a Microsoft ActiveX Data Objects (ADO)
Recordset from an Excel worksheet that is open in Excel, a memory leak occurs
in the Excel process. Repeated queries may eventually cause Excel to run out of
memory and raise an error, or cause Excel to stop responding.
The memory used by the ADO queries cannot be reclaimed by
closing and releasing the ADO objects. The only way to release the memory is to
quit Excel.
If possible, query the Excel worksheet only while the
file is not open in Excel.
If the worksheet must remain open (for
example, to allow dynamic recalculation of worksheet values on an ongoing
basis) use one of the following methods to work around the behavior:
Method 1
•
Use the SELECT INTO syntax of the Jet OLE DB Provider to
export the Excel data to a new worksheet.
For additional information about using the SELECT INTO syntax to export
data, click the following article number to view the article in the Microsoft Knowledge Base:
295646 (http://support.microsoft.com/kb/295646/)
How To Transfer Data from ADO Data Source to Excel with ADO
Method 2
•
Use the SaveCopyAs method of the Workbook object in the Excel object model to programmatically save the
open Excel file under a new name. You can then query the copy of the file that
you previously saved under a new name from the ADO application.
Create or locate an Excel worksheet with rows and columns
of data that can be queried using ADO. For example, you can use Excel to import
the Customers table from the sample Northwind Access database.
2.
In Visual Basic 6.0, create a Standard EXE project. By
default, Form1 is created. Set a reference to ADO.
3.
Add a module to the project, and then enter the following
declarations for application programming interface (API) calls that allow you
to check memory usage using Performance Monitor counters:
Option Explicit
'Performance monitor functions for Visual Basic from PDH.DLL
Declare Function PdhVbOpenQuery Lib "pdh.dll" _
(ByRef QueryHandle As Long) As Long
Declare Function PdhCloseQuery Lib "pdh.dll" _
(ByVal QueryHandle As Long) As Long
Declare Function PdhVbAddCounter Lib "pdh.dll" _
(ByVal QueryHandle As Long, ByVal CounterPath As String, _
ByRef CounterHandle As Long) As Long
Declare Function PdhRemoveCounter Lib "pdh.dll" _
(ByVal CounterHandle As Long) As Long
Declare Function PdhCollectQueryData Lib "pdh.dll" _
(ByVal QueryHandle As Long) As Long
Declare Function PdhVbGetDoubleCounterValue Lib "pdh.dll" _
(ByVal CounterHandle As Long, ByRef CounterStatus As Long) As Double
Declare Function PdhVbIsGoodStatus Lib "pdh.dll" _
(ByVal StatusValue As Long) As Long
Declare Function PdhVbGetOneCounterPath Lib "pdh.dll" _
(ByVal PathString As String, ByVal PathLength As Long, _
ByVal DetailLevel As Long, ByVal CaptionString As String) As Long
Declare Function PdhVbCreateCounterPathList Lib "pdh.dll" _
(ByVal DetailLevel As Long, ByVal CaptionString As String) As Long
Declare Function PdhVbGetCounterPathFromList Lib "pdh.dll" _
(ByVal Index As Long, ByVal Buffer As String, _
ByVal BufferLength As Long) As Long
Declare Function PdhVbGetCounterPathElements Lib "pdh.dll" _
(ByVal PathString As String, ByVal MachineName As String, _
ByVal ObjectName As String, ByVal InstanceName As String, _
ByVal ParentInstance As String, ByVal CounterName As String, _
ByVal BufferSize As Long) As Long
4.
Add a command button to Form1, and then insert the
following code in the Click event. This code repeatedly queries an Excel file
and displays memory usage in the Debug (Immediate) window.
Dim cn As ADODB.Connection
Dim rs As ADODB.Recordset
Dim i As Integer
Dim max As Integer
Dim r As Long
Dim hPDHQuery As Long 'Handle to performance monitor query
Dim hPDHCounter As Long 'Handle to performance monitor counter
Dim strCounterPath 'Path to performance monitor counter
Dim lngCounterStatus As Long 'Status of counter when checked
Dim dblPrivateBytes As Double 'Value of counter when checked
Set cn = New ADODB.Connection
'Jet connection string.
cn.Open "Provider=Microsoft.Jet.OLEDB.4.0;" & _
"Data Source=" & App.Path & "\test.xls;" & _
"Extended Properties=Excel 8.0"
'Initialize PDH query object.
r = PdhVbOpenQuery(hPDHQuery)
'Initialize counter.
'Edit the value of the "strCounterPath" variable.
strCounterPath = "\\<computername>\Process(Excel)\Private Bytes"
r = PdhVbAddCounter(hPDHQuery, strCounterPath, hPDHCounter)
'Gather data.
r = PdhCollectQueryData(hPDHQuery)
'Get counter value and process data.
dblPrivateBytes = PdhVbGetDoubleCounterValue(hPDHCounter, _
lngCounterStatus)
If PdhVbIsGoodStatus(lngCounterStatus) Then
Debug.Print "Memory used by Excel: " & CLng(dblPrivateBytes)
Else
Debug.Print "Invalid data."
End If
'Edit the value of the "max" variable.
max = 100
ReDim alngPrivateBytes(max)
For i = 1 To max
Set rs = New ADODB.Recordset
rs.CursorLocation = adUseClient
'Edit the query to reflect the name of the worksheet.
rs.Open "SELECT * FROM [Customers$]", cn
Do Until rs.EOF
rs.MoveNext
Loop
rs.Close
Set rs = Nothing
r = PdhCollectQueryData(hPDHQuery)
'Get counter value and process data.
dblPrivateBytes = PdhVbGetDoubleCounterValue(hPDHCounter, _
lngCounterStatus)
'Process data.
If lngCounterStatus = 0 Then
Debug.Print "Memory used by Excel: " & CLng(dblPrivateBytes)
alngPrivateBytes(i) = CLng(dblPrivateBytes)
Else
Debug.Print "Invalid data."
alngPrivateBytes(0) = 0
End If
Next
cn.Close
Set cn = Nothing
Debug.Print "Total increase for " & max & " iterations: " & _
(CStr(alngPrivateBytes(max) - alngPrivateBytes(0)))
Debug.Print "Average increase per iteration: " & _
(CStr((alngPrivateBytes(max) - alngPrivateBytes(0))) / max)
'Clean up.
r = PdhRemoveCounter(hPDHCounter)
r = PdhCloseQuery(hPDHQuery)
5.
Make the following changes in the code:
•
Edit the Jet connection string to reflect the location
of the Excel test file. Note: It is commented as follows: 'Jet connection string.
•
Edit the value of the "strCounterPath" variable to use
the local workstation name. Note: It is commented as follows: 'Edit the value of the
"strCounterPath" variable.
•
Edit the query to reflect the name of the worksheet in
the file with the test data. Note: It is commented as follows: 'Edit the query to reflect the name
of the worksheet.
•
Edit the value of the "max" variable for the desired
number of repetitions. Note: It is commented as follows: 'Edit the value of the "max"
variable.
6.
Run the Excel application, and then open the test Excel
file.
7.
Run the Visual Basic application. Note that there is a
steady increase in memory that is used by the Excel process, even though the
ADO objects have been closed and released.
For additional information, click the following article number to view the article in the Microsoft Knowledge Base:
257819 (http://support.microsoft.com/kb/257819/)
How To Use ADO with Excel Data from Visual Basic or VBA
For additional information
about the use of performance counters from Visual Basic, click the following article number to view the article in the Microsoft Knowledge Base:
296526 (http://support.microsoft.com/kb/296526/)
INFO: Collecting Performance Data Using PDH APIs from Visual Basic
For additional
information about Excel export options, click the article numbers below to view
the articles in the Microsoft Knowledge Base:
247412 (http://support.microsoft.com/kb/247412/EN-US/) INFO: Methods for Transferring Data to Excel from Visual Basic
246335 (http://support.microsoft.com/kb/246335/) How To Transfer Data from an ADO Recordset to Excel with Automation
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