Very slow itab loop with nested SELECTs - abap

Question

I have declare an internal table like:
DATA: wa_collectoraction TYPE zcollectoraction,
it_collectoraction LIKE STANDARD TABLE OF zcollectoraction.
Then I fill the table with:
SELECT bukrs kunnr yearmonth MAX( dat ) AS dat
FROM zcollectoraction
INTO CORRESPONDING FIELDS OF TABLE it_collectoraction
WHERE bukrs IN so_bukrs AND
kunnr IN so_kunnr AND
dat IN so_date
GROUP BY bukrs kunnr yearmonth.
and finally I have the following loop
LOOP AT it_collectoraction INTO wa_collectoraction.
PERFORM progress_bar USING 'Retrieving data...'(035)
sy-tabix
i_tab_lines.
"Get the MAX TIME for all lines in order to cover the case we have more than 1 line."
SELECT SINGLE * FROM zcollectoraction
INTO CORRESPONDING FIELDS OF wa_collectoraction
WHERE bukrs = wa_collectoraction-bukrs AND
kunnr = wa_collectoraction-kunnr AND
dat = wa_collectoraction-dat AND
time = ( SELECT MAX( time ) AS time
FROM zcollectoraction
WHERE bukrs = wa_collectoraction-bukrs AND
kunnr = wa_collectoraction-kunnr AND
dat = wa_collectoraction-dat ).
MODIFY it_collectoraction FROM wa_collectoraction.
ENDLOOP.
This loop is doing 5 minutes for 3000 records.
Can someone tell me what to do in order to be faster?
Thanks in advance

Answer 1

The best tool to analyze a standalone report's performance is ST12, so if you have the chance, trace it.
Without a trace, we have to guess, the biggest problem is either the SELECT with the subSELECT, or the MODIFY.
1) SELECTs in a LOOP are always slow
Here you actually make two for every line in it_collectoraction.
Try reducing the number of SELECTs
Depending on the number of lines with the same dat, it might be much faster to replace the SELECT in the LOOP with a SELECT with FOR ALL ENTRIES from zcollectoraction outside the LOOP, and find the MAX(time) on ABAP side.
Index coverage
Seems to be fine.
2) MODIFY is slow on STANDARD tables
You have to sieve through the whole table just to find the relevant line. If you define it_collectoraction as SORTED, this will be much faster. If you use a field symbol in the LOOP, it can be avoided altogether.
Coding
Replace your LOOP with this:
TYPES: BEGIN OF tty_coll_act,
bukrs TYPE burks,
kunnr TYPE kunnr,
dat TYPE dat,
time TYPE time,
END OF tty_coll_act.
DATA: lt_coll_act TYPE TABLE OF tty_coll_act,
ls_coll_act LIKE LINE OF lt_coll_act.
FIELD-SYMBOLS: <fs_collectoraction> LIKE LINE OF it_collectoraction.
SELECT bukrs kunnr dat time
INTO TABLE lt_coll_act
FROM zcollectoraction
FOR ALL ENTRIES IN it_collectoraction
WHERE bukrs = wa_collectoraction-bukrs AND
kunnr = wa_collectoraction-kunnr AND
dat = wa_collectoraction-dat.
SORT lt_coll_act BY bukrs kunnr dat time DESCENDING.
LOOP AT it_collectoraction ASSIGNING <fs_collectoraction>.
" the READ TABLE finds the first matching row,
" it will be MAX(TIME) as TIME is sorted descending
READ TABLE lt_coll_act INTO ls_coll_act
WITH KEY bukrs = <fs_collectoraction>-bukrs
kunnr = <fs_collectoraction>-kunnr
dat = <fs_collectoraction>-dat BINARY SEARCH.
<fs_collectoraction> = ls_coll_act.
ENDLOOP.

Answer 2

Instead of adding a selection query inside a loop, get all data into an internal table and handle it with read statements inside the loop.
Adding select queries inside a loop will always slow down the execution of an application as the application has to execute database queries for each loop. Loading all required information into an internal table and then handling data within the application is much more faster.
Let me know if you require any further details on this.

Answer 3

First of all I want to thank all of you for your help.
I change the logic of select by using an internal table with all records from dbtab according to the selection data of the user.
So the code became as follow:
DATA: wa_collectoraction TYPE zcollectoraction,
it_collectoraction TYPE TABLE OF zcollectoraction,
itsort_collectoraction TYPE HASHED TABLE OF zcollectoraction
WITH UNIQUE KEY mandt bukrs kunnr yearmonth dat time.
FIELD-SYMBOLS: <fs_collectoraction> LIKE LINE OF it_collectoraction.
SELECT bukrs kunnr yearmonth MAX( dat ) AS dat
FROM zcollectoraction
INTO CORRESPONDING FIELDS OF TABLE it_collectoraction
WHERE bukrs IN so_bukrs AND
kunnr IN so_kunnr AND
dat IN so_date
GROUP BY bukrs kunnr yearmonth.
" Keep the total records which will be inserted.
i_tab_lines = sy-dbcnt.
SELECT * INTO TABLE itsort_collectoraction
FROM zcollectoraction
WHERE bukrs IN so_bukrs AND
kunnr IN so_kunnr AND
dat IN so_date.
SORT itsort_collectoraction
BY mandt bukrs kunnr yearmonth dat time DESCENDING.
LOOP AT it_collectoraction ASSIGNING <fs_collectoraction>.
PERFORM progress_bar USING 'Retrieving data...'(035)
sy-tabix
i_tab_lines.
READ TABLE itsort_collectoraction INTO wa_collectoraction
WITH KEY bukrs = <fs_collectoraction>-bukrs
kunnr = <fs_collectoraction>-kunnr
yearmonth = <fs_collectoraction>-yearmonth
dat = <fs_collectoraction>-dat.
<fs_collectoraction> = wa_collectoraction.
ENDLOOP.
This code run 43000 records in 1 minute.
The only problem is that after the first 10000 to 15000 records the process is slowing down. I don't know if there is any command to clear sth. I don't know what to clear.
Again thanks a lot all of you.
Regards
Elias
PS. In the 1st 10 sec it process 14.000 records.
In 1 minute process 38.500 and
In 1 minute & 50 seconds finished the 54.500 records.
It gives me the impression that it fulfills sth which slow-down the process. ANY IDEA?

Answer 4

I am a little late to the party, but what I see in your first post is that you just want to read the latest (max(date) and max(time)) entries from one table per bukrs and kunnr?
Use one select to get the table's content. Select only by keyfields or indexes:
I assume that date is not a key field, but bukrs and kunnr:
SELECT bukrs kunnr yearmonth dat time
FROM zcollectoraction
INTO CORRESPONDING FIELDS OF TABLE it_collectoraction
WHERE bukrs IN so_bukrs AND
kunnr IN so_kunnr
.
Delete non key fields from itab:
DELETE it_collectoraction WHERE dat NOT IN so_date.
Sort itab by date and time descending so that the latest entry is the first combination of bukrs and kunnr
SORT it_collectoraction BY bukrs kunnr date DESCENDING time DESCENDING.
Delete all adjacent (=all with same compare key after the first) entries per bukrs and kunnr
DELETE ADJACENT DUPLICATES FROM it_collectoraction COMPARING bukrs kunnr.