Surprising results on BSEG

Question

I read that  instead of using BSEG, using index tables BSIS & BSA, we can improve performance. We have a old code in our system and I tried to modify using BSIS & BSAS... but my changes are taking more time than the old code.
Old:
loop at TEMPBKPF.
Keep index
  tmpidx = sy-tabix.
Transfering Sy-MANDT value.
  TEMPBKPF-MANDT = SY-MANDT.
  select        BUKRS            "Company Code
                BELNR            "Accounting document number
                GJAHR            "Fiscal year
                BUZEI            "Number of Line Item Within Accounting
                                 "Document
                SHKZG            "Debit/credit indicator
                DMBTR            "Amount in local currency
                SGTXT            "Item Text
                KOSTL            "Cost Center
                HKONT            "General ledger account
                PRCTR            "Profit Center
    into (tempbseg-bukrs,
          tempbseg-belnr,
          tempbseg-gjahr,
          tempbseg-buzei,
          tempbseg-shkzg,
          tempbseg-dmbtr,
          tempbseg-sgtxt,
          tempbseg-kostl,
          tempbseg-hkont,
          tempbseg-prctr)
    from BSEG                    "[Accounting Document Segment]
   where BUKRS = tempbkpf-bukrs  "Company Code
     and GJAHR = tempbkpf-gjahr  "Fiscal year
     and BELNR = tempbkpf-belnr. "Accounting document Number.
        TEMPBSEG-MANDT = SY-MANDT.
        append TEMPBSEG.
Updating TEMPBKPF internal table.
  endselect.
  modify tempbkpf index tmpidx.
endloop.
My Code:
I replaced the loop with FOR ALL ENTRIES & used BSIS & BSAS
access the index tables, for each record in bseg
  SELECT bukrs
         hkont
         gjahr
         belnr
         buzei
         shkzg
         dmbtr
         sgtxt
         kostl
         prctr
         INTO TABLE i_bsis
         FROM bsis
         FOR ALL ENTRIES IN i_bkpf[]
        WHERE bukrs EQ i_bkpf-bukrs        " Company Code
          AND gjahr EQ i_bkpf-gjahr        " Fiscal year
          AND belnr EQ i_bkpf-belnr.       " Accounting document Number.
  IF sy-subrc EQ 0.
    SORT i_bsis.
  ENDIF.
  SELECT bukrs
         hkont
         gjahr
         belnr
         buzei
         shkzg
         dmbtr
         sgtxt
         kostl
         prctr
         INTO TABLE i_bsas
         FROM bsas
         FOR ALL ENTRIES IN i_bkpf[]
        WHERE bukrs EQ i_bkpf-bukrs        " Company Code
          AND gjahr EQ i_bkpf-gjahr        " Fiscal year
          AND belnr EQ i_bkpf-belnr.       " Accounting document Number.
  IF sy-subrc EQ 0.
    SORT i_bsas.
  ENDIF.
Finally, I will loop through both these itabs and build my final itab.
Any thoughts please.
Thanks,
Kiran

Answer 1

I don't know where you read that you should avoid BSEG and use BSIS and BSAS instead, but you should have read Please Read before Posting in the Performance and Tuning Forum instead.
You can also have a look at [Performance - what will kill you and what will leave you with only a flesh wound|/people/rob.burbank/blog/2006/11/16/performance--what-will-kill-you-and-what-will-leave-you-with-only-a-flesh-wound]
A SELECT/ENDSELECT within a loop is something we generally try to avoid, but in your old code, it was using the primary key; in the new code, it is using two SELECTS with at best a secondary index (depending on your release). Then you LOOP through both table to create a final table. But both BSIS and BSAS have the same structure. You could have used the APPENDING option on the second SELECT and avoided some extra work (both programming and execution time).
Finally, depending on what you are trying to do, you will be missing any line items against customers and vendors. BSIS and BSAS have only GL items.
Rob
Edited by: Rob Burbank on Jun 25, 2010 9:59 AM