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Siddharth_Shah
Explorer
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:

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