oracle delete data from table with rownum - oracle

Question

I have a procedure that deletes the data from table1. Five instances of the procedure running the same time and all ran without any error/exception.
But still, there are many records in the table1 where EndTime <= v_purgedate. Please help.
declare
rowcount1 NUMBER;
begin
LOOP
delete table1 eh
where eh.EndTime <= v_purgedate
and rownum <= 30000 ;
rowcount1 := rowcount1 + sql%rowcount;
commit;
exit when rowcount1=0;
rowcount1=0;
END LOOP;
end;
/

Answer 1

You are trying to do what is called "do it yourself parallelism", as opposed to the parallel processing that Oracle can do by itself if you ask nicely.
There is a package called DBMS_PARALLEL_EXECUTE that does this for you. You split the data into chunks (based on ROWIDs or numbers), then call the RUN_TASK procedure to process each chunk, either serially or in parallel. There is one commit per chunk.
Here is a demonstration that deletes 30,000 rows per commit. First, test data:
SQL> create table table1(endtime) as
2 select trunc(sysdate) - level/24 from dual
3 connect by level <= 240000;
Table TABLE1 created.
SQL> insert into table1 select * from table1;
240,000 rows inserted.
SQL> insert into table1 select * from table1;
480,000 rows inserted.
SQL> insert into table1 select * from table1;
960,000 rows inserted.
SQL> select count(*) from table1;
COUNT(*)
----------
1920000
Now, here is the code:
SQL> declare
2 l_task_name varchar2(128) := 'Delete_TABLE1';
3 l_sql_chunk clob := q'§
4 select date '2100-01-01' - min(endtime) start_id,
5 date '2100-01-01' - max(endtime) end_id,
6 chunk
7 from (
8 select endtime,
9 ceil(row_number() over(order by endtime) / 30000) chunk
10 from table1 where endtime < sysdate - 8000
11 )
12 group by chunk
13 §';
14 l_sql_run clob := q'§
15 delete from table1
16 where endtime between
17 date '2100-01-01' - :start_id and
18 date '2100-01-01' - :end_id
19 §';
20 l_boolean boolean := false;
21 task_not_found EXCEPTION;
22 PRAGMA EXCEPTION_INIT(task_not_found, -29498);
23 begin
24 begin
25 DBMS_PARALLEL_EXECUTE.DROP_TASK (l_task_name);
26 exception when task_not_found then null;
27 end;
28 DBMS_PARALLEL_EXECUTE.CREATE_TASK (l_task_name);
29 DBMS_PARALLEL_EXECUTE.CREATE_CHUNKS_BY_SQL (
30 task_name => l_task_name,
31 sql_stmt => l_sql_chunk,
32 by_rowid => l_boolean
33 );
34 DBMS_PARALLEL_EXECUTE.RUN_TASK (
35 task_name => l_task_name,
36 sql_stmt => l_sql_run,
37 language_flag => 1,
38 parallel_level => 0 -- 0 for serial, 2+ for parallel
39 );
40 end;
41 /

Answer 2

you have an endless Loop, because rowcount1 will never be 0 when your table contains data that will be deleted.
i think what you what is
declare
rowcount1 NUMBER;
begin
LOOP
delete table1 eh
where eh.EndTime <= v_purgedate -- you should also initialize a variable
and rownum <= 30000 ;
--rowcount1 := rowcount1 + sql%rowcount;
commit;
exit when sql%rowcount = 0;
rowcount1=0;
END LOOP;
end;
/

Answer 3

When you declare the variable rowcount1, you do not assign any number to it, so its value is NULL. Afterwards, when you add a number to NULL the result is always NULL. This is surely not what you want. To illustrate:
SQL> declare
2 rowcount1 NUMBER;
3 begin
4 dbms_output.put_line('<'||rowcount1||'>');
5 rowcount1 := rowcount1 + 1;
6 dbms_output.put_line('<'||rowcount1||'>');
7 end;
8 /
<>
<>
PL/SQL procedure successfully completed.
It seems your code will go in an endless loop. You say that is not the case, so clearly you are not showing us any real code.
Anyway, this is not a good way to do what you want. I'll post another answer saying why.
Regards, Stew Ashton

Answer 4

It's a easy code for delete data in a table .
Try it.
declare
cursor c is
select * from table1 where rownum<=30000;
begin
for i in c loop
delete from table1 where EndTime <= v_purgedate;
end loop;
commit;
end;