Performance Impact due to Memory Allocation

[Siddharth_Shah]

Hi All,

Memory plays important role in performance of the program. I am writing this blog to explain why we should give equal importance to memory we are allocating to variables/internal tables.

Lets say I have fetched 100000 records from BSEG table and stored in one internal table (say LT_BSEG). As soon as I gets 100000 records into LT_BSEG table, LT_BSEG internal table gets allocated with required memory.

select * from bseg into table @data(lt_bseg) UP TO 100000 rows.

 

Now I am processing this 100000 records and calculating how much time it takes.

loop at lt_bseg ASSIGNING FIELD-SYMBOL(<lfs_bseg>).

  <lfs_bseg>-sgtxt = 'Changing Text Value'.

ENDLOOP.



GET TIME STAMP FIELD lv_t2.



lv_diff1 = lv_t2 - lv_t1.

On second instance I am copying LT_BSEG to another internal table LT_BSEG_COPY. As soon as i am copying, further memory gets allocated to LT_BSEG_COPY.

At this time, I have got memory allocated for two Internal tables having 100000 rows each.

Now I am processing same 100000 records again and calculating how much time it takes.

data(lt_bseg_copy) = lt_bseg[].

GET TIME STAMP FIELD lv_t1.



loop at lt_bseg ASSIGNING <lfs_bseg>.

  <lfs_bseg>-sgtxt = 'Changing Text Value'.

ENDLOOP.



GET TIME STAMP FIELD lv_t2.



lv_diff2 = lv_t2 - lv_t1.



lv_percentage =  ( lv_diff2   / lv_diff1 ) .

On Third instance I am FREEing memory from unwanted internal table (LT_BSEG_COPY) and does same processing on those 100000 records and calculating how much time it takes.

 

********************************

****** FREEing Memory *********

********************************

FREE lt_bseg_copy.

loop at lt_bseg ASSIGNING <lfs_bseg>.

  <lfs_bseg>-sgtxt = 'Changing Text Value'.

ENDLOOP.



GET TIME STAMP FIELD lv_t2.



lv_diff3 = lv_t2 - lv_t1.

 

I have got 6 times impact on performance when I copied internal table to another internal table and processed same number of rows.

 

Code:

DATA:      lv_t1    TYPE timestampl,

           lv_t2    TYPE timestampl,

           lv_diff1        type p DECIMALS 2,

           lv_diff2        type p DECIMALS 2,

           lv_diff3        type p DECIMALS 2,

           lv_percentage        type i.



select * from bseg into table @data(lt_bseg) UP TO 100000 rows.





cl_demo_output=>begin_section( | Processing Internal table having { lines( lt_bseg ) } rows |  ).

*********************************************************

****** Memory Allocated to One Internal Table *********

*********************************************************

cl_demo_output=>begin_section( |Memory Allocated to one internal table | ).



GET TIME STAMP FIELD lv_t1.



loop at lt_bseg ASSIGNING FIELD-SYMBOL(<lfs_bseg>).

  <lfs_bseg>-sgtxt = 'Changing Text Value'.

ENDLOOP.



GET TIME STAMP FIELD lv_t2.



lv_diff1 = lv_t2 - lv_t1.



cl_demo_output=>write_text( |Time Taken to process { lines( lt_bseg ) } rows is - { lv_diff1 }|  ).



*********************************************************

****** Memory Allocated to TWO Internal Tables *********

************ ITAB COPY *********************************

*********************************************************

data(lt_bseg_copy) = lt_bseg[].



cl_demo_output=>begin_section( | Memory Allocated to two internal table | ).



GET TIME STAMP FIELD lv_t1.



loop at lt_bseg ASSIGNING <lfs_bseg>.

  <lfs_bseg>-sgtxt = 'Test'.

ENDLOOP.



GET TIME STAMP FIELD lv_t2.



lv_diff2 = lv_t2 - lv_t1.



cl_demo_output=>write_text( |Time Taken to process { lines( lt_bseg ) } rows is - { lv_diff2 }|  ).



lv_percentage =  ( lv_diff2   / lv_diff1 ) .

cl_demo_output=>write_text( |Performance decreased by { lv_percentage } times | ).





********************************

****** FREEing Memory *********

********************************

FREE lt_bseg_copy.



cl_demo_output=>begin_section( |Deallocating memory from one of the internal table|  ).

GET TIME STAMP FIELD lv_t1.



loop at lt_bseg ASSIGNING <lfs_bseg>.

  <lfs_bseg>-sgtxt = 'Test'.

ENDLOOP.



GET TIME STAMP FIELD lv_t2.



lv_diff3 = lv_t2 - lv_t1.



cl_demo_output=>write_text( |Time Taken to process { lines( lt_bseg ) } rows is - { lv_diff3 }|  ).

lv_percentage =  ( lv_diff2   / lv_diff3 ) .

cl_demo_output=>write_text( |Performance again increased by { lv_percentage } times| ).





cl_demo_output=>display( ).

 

Output: