Bdc questions asked in interv

Question

Hi all
pls clarify doughts on below.
1. what is meant by synchronous and asynchronous ?  how can u capture errors while using call transaction in both synchronous and asynchronous.
pls tell the code.
2. while large amount of data is coming in  a file  , i want to split the  some amount of data into number of sessions( it may be 6 or 7 sessions  ) with same name of session  . how can we do this .

Answer 1

Hi Nagendra,
                  In the “CALL TRANSACTION USING” statement, you can specify the update mode as synchronous or asynchronous.  To restate the difference:
Synchronous updating indicates that an update is completed for the transaction before processing returns to the “calling” program.
Asynchronous updating indicates that processing returns to the “calling” program immediately after the transaction is completed, even before the update is completed.
The difference in these update modes creates a trade-off between the execution speed and the meaning of the return code.
With respect to the execution speed:
Synchronous updating is slower than asynchronous updating because processing does not return to the “calling” program until the update is complete. 
Remember that the update mode when processing batch input sessions is always synchronous.
With respect to the meaning of the return code:
The return code (SY-SUBRC) after synchronous updating indicates the success or failure of the actual update.  The return code after asynchronous updating only indicates the success or failure of the transaction, not the update.
Starting with the 3.1 release it is possible to specify the update mode also when we create a BDC session via a BDC program by setting the POST_LOCAL parameter equal to ‘X’ which would then set the update to asynchronous. 
This is synchronous :
DO.
     PERFORM FILL_BDC_TAB.
     CALL TRANSACTION ‘FK02’
          USING          BDC_TAB
          MODE          ‘N’
          UPDATE          ‘S’.
     IF SY-SUBRC <> 0.
          WRITE: / ‘Error’.
     ENDIF.
ENDDO.
With synchronous updating, we can check SY-SUBRC to determine the success of the transaction and the actual update to the database.
This is asynchronous ::
DO.
     PERFORM FILL_BDC_TAB.
     CALL TRANSACTION ‘FK02’
          USING          BDC_TAB
          MODE          ‘N’
          UPDATE          ‘A’.
     IF SY-SUBRC <> 0.
          WRITE: / ‘Transaction error’.
     ENDIF.
ENDDO.
With asynchronous updating, we can check SY-SUBRC to determine the success of the transaction only, not the actual update to the database
Error Handling :
With the “CALL TRANSACTION USING” statement (and the “CALL DIALOG” statement), errors are not handled automatically by the system.  Therefore, you must handle these errors in the batch input program.
After a “CALL TRANSACTION USING” statement (or a “CALL DIALOG” statement), the value of SY-SUBRC indicates the success or failure  of the transaction:
If SY-SUBRC is zero, the transaction (or dialog module) was successful.
If SY-SUBRC is not zero, the transaction (or dialog module) was  not successful.
You can handle an error in many ways:
Write an error report.
Send the record(s) in error to an error file.
Create a batch input session with the record(s) in error.
This list of error handling methods is not complete.  The exact method chosen will depend on your specific requirements.  Also, these methods can be combined (i.e., you can create an error report and send the records in error to an error file).
For ur second query read this.. It may be helpful..
The “BDC_INSERT” function module inserts transaction data into a batch  input session.
The exporting parameters are:
Tcode (required) - The transaction code that is to be executed.  In other words, the information in the BDC table refers to this transaction.
POST_LOCAL - if you set this parameter to ‘X’ the update will run in asynchronous mode instead of the default synchronous one (for the differences between the two update types see the chapter on CALL TRANSACTION)
The only tables parameter is:
Dynprotab (required) - The BDC table with the transaction data.
The “BDC_INSERT” function module is “called” for each transaction entered into the batch input session.
In our simple example where we update one vendor, we will only “call” this function module once.
In a more realistic example where we will read multiple records from a sequential file, we will “call” this function module for each record.
A batch input session can include data for different transactions.  The “TCODE” parameter indicates the appropriate transaction code.  The BDC table contents must mimic the transaction code specified or an error will occur when the batch input session is processed.
For example, if you read vendor information from a sequential file, you will use the “Change Vendor” transaction (“FK02”) if the vendor already exists or the “Create Vendor” transaction (“FK01”) if the vendor does not exist.  The BDC table for each of these transactions will be different because different screens are encountered and different fields must be filled.
Post local is a new, 4.0 parameter in the BDC_INSERT function module.
Reward Points if u find helpful.
Regards,
Rajesh