Microsoft KB Archive/251203

Knowledge Base

PRB: DAO OpenRecordset Hangs if Table and Index Name Are Over 63 Characters

Article ID: 251203

Article Last Modified on 4/22/2003

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APPLIES TO

• Microsoft Visual Basic 5.0 Professional Edition
• Microsoft Visual Basic 6.0 Professional Edition
• Microsoft Visual Basic 5.0 Enterprise Edition
• Microsoft Visual Basic 6.0 Enterprise Edition

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This article was previously published under Q251203

SYMPTOMS

Microsoft Visual Basic appears to hang on the OpenRecordset method when opening a Microsoft SQL Server 7.0 table as a dbOpenDynaset when either the table name or the combination of the table name and any index name is longer than 63 characters.

If you launch Task Manager, the VB6.exe process uses approximately 99 percent of the processor time (on a single processor machine) and allocates memory quickly.

RESOLUTION

Either of the following are workarounds for the problem:

1. Rename the SQL Server table or index so that the combination of names is 63 characters or fewer.
   

Open the recordset with dbOpenSnapshot or dbOpenForwardOnly instead of dbOpenDynaset.

1. Open the recordset with dbOpenSnapshot or dbOpenForwardOnly instead of dbOpenDynaset.

Both workarounds are illustrated in the code below.

MORE INFORMATION

Steps to Reproduce Behavior

1. Run the following script on SQL Server 7.0 in the pubs database to create the table and an index. The table name is 31 characters long and the index name is 33 characters long.

   Use Pubs
   GO
   
   if exists (select * from sysobjects where id = object_id(N'[dbo].[MyTableNameIsThirtyOneCharacter]') 
   and OBJECTPROPERTY(id, N'IsUserTable') = 1)
   drop table [dbo].[MyTableNameIsThirtyOneCharacter]
   GO
   
   CREATE TABLE [dbo].[MyTableNameIsThirtyOneCharacter] (
   [id] [int] NOT NULL ,
   [fld1_char] [char] (10) NULL 
   ) ON [PRIMARY]
   GO
   
   CREATE  UNIQUE  INDEX [I_MyTableNameIsThirtyOneCharacter] ON [dbo].[MyTableNameIsThirtyOneCharacter]([id]) ON [PRIMARY]
   GO
   
   INSERT MyTableNameIsThirtyOneCharacter(id, fld1_char)
   VALUES(1, "Record1")
   GO
   
   INSERT MyTableNameIsThirtyOneCharacter(id, fld1_char)
   VALUES(2, "Record2")
   GO
                       

2. Create a new Visual Basic Standard EXE project. Form1 is created by default.
3. From the Project menu, select References , and make a reference to the DAO 3.51 Object Library.

4. Add the following code to the Form_Load() Event:

   Dim daoDB As Database
      Dim rs As DAO.Recordset
      
   'You will need to create an ODBC DSN, pointing to the SQL Server Pubs database.
      Set daoDB = DBEngine.OpenDatabase("Pubs_DSN", dbDriverNoPrompt, True, "ODBC;DATABASE=pubs;UID=sa;PWD=;DSN=DSN_Name")
   
      Set rs = daoDB.OpenRecordset("MyTableNameIsThirtyOneCharacter", dbOpenDynaset, dbSeeChanges)
   
      'If you remove the comment marker from this line and comment out the dbOpenDynaset line below, it will be successful.
      'Set rs = daoDB.OpenRecordset("MyTableNameIsThirtyOneCharacter", dbOpenSnapshot)  'You could also use dbOpenForwardOnly
   
      'If you rename the SQL Server table and remove a few characters from the name and reference the new shorter table name, 
      'this line will be successful.
   
      Set rs = daoDB.OpenRecordset("MyTableNameIsThirtyOneCharacter", dbOpenDynaset, dbSeeChanges)
      
      rs.Close
      daoDB.Close
      Set rs = Nothing
      Set daoDB = Nothing
                       

5. Edit the OpenDatabase line to refer to a DSN that points to your SQL Server.
6. Save the project if you want to run it more than once, because running the code forces you to end the VB6.exe process.
7. Step through the project. Visual Basic should appear to hang on the OpenRecordset.
8. Start Task Manager and note VB6.exe is monopolizing the CPU and allocating memory quickly. You need to end the VB6.exe process.

NOTE: This behavior occurs only when using DAO 3.5x and Jet 3.5x, and accessing a SQL Server 7.0 table. The problem does not occur with DAO/Jet 3.5x and a SQL Server 6.5 table (SQL Server 6.5 object names are restricted to 30 characters). It does not occur when using DAO 3.6 and Jet 4.0 with either version SQL Server 6.5 or 7.0, and also does not occur when accessing a Microsoft Access database.

Additional query words: cpu spin memory leak

Keywords: kbbug kbdatabase kbprb KB251203

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