TechTip: Native OLE DB vs. ODBC

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They're the age-old questions: Paper or plastic? Boxers or briefs? OLE DB or ODBC? OK, maybe that last one needs some explanation. To access your iSeries database from a Windows-based client application, you have several options to choose from. Determining which of these is the best solution can be dizzying. I'll help you figure out which one is best for you, be it IBM's native OLE DB provider, an ODBC data source name (DSN), or an ODBC connection without DSN ("DSNless") .

IBMDA400

IBM introduced its OLE DB database provider with V3R1M3 of Client Access. Originally named "Project Lightning," this provider was designed to give software developers fast record-level access to the iSeries database. The concept behind OLE DB is basically to give a common interface to dissimilar data sources. This means that the same technique used to access an iSeries database can be used to access a Microsoft SQL Server database or an Oracle database.

OLE DB providers are accessed through ActiveX Data Objects (ADO). ADO acts as the programming interface to OLE DB. The early version of the IBMDA400 OLE DB provider only supported a subset of the functionality available through ADO. The RecordCount property of the Recordset object, for example, was not available. This property is used to determine the number of records contained within a recordset. The functionality has been greatly enhanced in recent versions of the IBMDA400 provider.

ODBC

When we talk about using ODBC with ADO, what we're actually talking about is using the Microsoft OLE DB provider for ODBC databases. There are two options for how to use an ODBC data source with ADO. The first option is to define an ODBC data source through the Windows ODBC control panel. This method is not usually preferred because it requires that the data source be configured on each client computer that would be using the ADO application. The second option is to create a DSNless ODBC. With this method, the connection is defined much as an OLE DB connection is defined, but with greater ADO object support. There is also a performance difference between these options, which I'll discuss later.

Making the Connection

These three methods use similar techniques to connect to a data source because ADO is used to access each database provider. The code below illustrates how to connect to a data source using the iSeries OLE DB provider using Visual Basic Scripting language (VBScript).

Set conn = CreateObject("ADODB.Connection")
Set rs = CreateObject("ADODB.Recordset")

conn.open "Provider=IBMDA400;User ID=user;Password=secret;" &  
                  "Data Source=192.168.0.1" 

rs.Open "SELECT * FROM QSYS2.SYSTABLES", conn

The key piece of this code is contained in the Open method of the connection object. The Provider parameter defines the OLE DB provider being used. The Data Source parameter identifies the iSeries' IP address. The User ID and Password parameters are self-explanatory. Below, you can see how this same piece of code would be defined using a DSNless connection.

Set conn = CreateObject("ADODB.Connection")
Set rs = CreateObject("ADODB.Recordset")

conn.open "DRIVER=iSeries Access ODBC Driver" & _ 
                 "UID=user; PWD=secret; System=192.168.0.1;"

rs.Open "SELECT * FROM QSYS2.SYSTABLES", conn

Notice that this example doesn't define the Provider parameter. This is because the default option here is to use the Microsoft OLE DB provider for ODBC databases. The same is true when you use an ODBC connection based on a defined ODBC DSN, as shown below.

Set conn = CreateObject("ADODB.Connection")
Set rs = CreateObject("ADODB.Recordset")

conn.open "DSN=AS400;UID=user; PWD=secret;"

rs.Open "SELECT * FROM QSYS2.SYSTABLES", conn

As I mentioned, this option assumes that you have defined an ODBC data source using the ODBC control panel icon. The advantage to this method is that the application can't be used on a machine that doesn't have the ODBC data source defined. The disadvantage is that the application can't be used on a machine that doesn't have the ODBC data source defined. While this seems a bit contradictory, the fact is that this method can be an advantage if you want to limit access to an application, but it's definitely a disadvantage in that each time an application is used on a different machine, the DSN must be configured on that machine first. The key deciding factor may ultimately be performance.

It's All Timing

To accurately examine how these alternatives perform, you need to test each option under similar circumstances. For the first test, make a connection from a code module within a Microsoft Access database. A version of this database can be downloaded from this Web site. Use the module code for the database, shown below, to test the speed of the ADO provider.

Option Compare Database

Sub ADOTest(ConnectionString As String, RecordSource As String)

Dim objConn As New ADODB.Connection
Dim objRs As New ADODB.Recordset

Rec = 0
strTime = Now()
Debug.Print "Start: " & strTime & Chr(13)
objConn.Open ConnectionString

objRs.Open RecordSource, objConn

Do Until objRs.EOF
objRs.MoveNext
Rec = Rec + 1
DoEvents
Loop
endTime = Now()
Debug.Print "End: " & endTime & Chr(13)

elapsed = DateDiff("s", strTime, endTime)
Debug.Print Rec & " records in " & elapsed; " seconds." & Chr(13)
Debug.Print (Rec / elapsed) & " records per second." & Chr(13)

objRs.Close
objConn.Close

End Sub

This simple Microsoft Access subroutine allows you to test multiple providers and SQL statements to determine which provider performs best under each circumstance. The ADOTest subroutine accepts two parameters: The first is the exact ConnectionString property required by the ADO Connection object; the second is the SQL statement you want to use as the record source for your recordset. This subroutine saves the current time to the variable strTime and then writes this value out to the Access debug window. Next, the routine establishes a connection to the data source through the object objConn. Once a connection is established, the recordset object objRs is opened using the supplied SQL statement. The routine then reads through all of the records in the recordset, while using the variable Rec as a counter of total records read. When the EOF condition occurs, the current time is saved again to the variable endTime, which is then used along with strTime and Rec to determine elapsed time in seconds and records read per second. You can test this routine by typing the following into the Visual Basic for Applications Immediate window within Microsoft Access:

Call ADOTest("Driver=iSeries Access ODBC Driver; System=192.168.0.1; 

UID=user; PWD=secret;","SELECT * FROM QSYS2.SYSTABLES")

Replace the System, UID, and PWD parameters with your iSeries IP address and a valid user ID and password for your iSeries.

The above example would run the test using the iSeries Access ODBC driver using a DSNless connection. To execute this same test using an OLE DB connection, use the following command:

Call ADOTest("Provider=IBMDA400; Data Source =192.168.0.1; User ID=user; 

Password=secret;","SELECT * FROM QSYS2.SYSTABLES")

Again, you need to replace the Data Source, User ID, and Password parameters with valid values for your system.

Finally, the code shown below would execute the test using the defined ODBC data source AS400.

Call ADOTest("DSN=AS400;UID=user; PWD=secret","SELECT * FROM QSYS2.SYSTABLES")

When you execute each of these commands, the system will return test results that indicate the start and end times, total elapsed time, number of records read, and records read per second. The table below shows comparative data returned by my system running V5R2.

Connection Type
Total Elapsed Time
Records Read
Records Per Second
DSNless ODBC
25 Seconds
32884
1315.36
ODBC DSN
26 Seconds
32885
1264.80
IBM OLE DB Provider
59 Seconds
32884
557.35

As this table shows, The DSNless ODBC connection exhibits the best performance, having read 1,315 records per second, while the performance of the OLE DB provider was worst, having taken more than twice as long to read the same number of records.

Wrapping It All Up

As you've seen here, the differences in defining each of the possible ADO providers are small, but the performance differences can be huge. And while an ODBC connection can be defined using an ODBC DSN, the DSNless connection actually offers slightly better performance--without the additional configuration requirement.

Mike Faust is IT Manager for The Lehigh Group in Macungie, Pennsylvania. Mike is also the author of the books The iSeries and AS/400 Programmer's Guide to Cool Things and Active Server Pages Primer from MC Press. You can contact Mike at This email address is being protected from spambots. You need JavaScript enabled to view it..



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