Strange behaviour of BULK COLLECT - oracle

Question

I tinkered together the following PL/SQL BULK-COLLECT which works astonishingly fast for updates on huge tables (>50.000.000). The only problem is, that it does not perform the updates of the remaining < 5000 rows per table. 5000 is the given limit for the FETCH instruction:
DECLARE
-- source table cursor (only columns to be updated)
CURSOR base_table_cur IS
select a.rowid, TARGET_COLUMN from TARGET_TABLE a
where TARGET_COLUMN is null;
TYPE base_type IS
TABLE OF base_table_cur%rowtype INDEX BY PLS_INTEGER;
base_tab base_type;
-- new data
CURSOR new_data_cur IS
select a.rowid,
coalesce(b.SOURCE_COLUMN, 'FILL_VALUE'||a.JOIN_COLUMN) TARGET_COLUMN from TARGET_TABLE a
left outer join SOURCE_TABLE b
on a.JOIN_COLUMN=b.JOIN_COLUMN
where a.TARGET_COLUMN is null;
TYPE new_data_type IS TABLE OF new_data_cur%rowtype INDEX BY PLS_INTEGER;
new_data_tab new_data_type;
TYPE row_id_type IS TABLE OF ROWID INDEX BY PLS_INTEGER;
row_id_tab row_id_type;
TYPE rt_update_cols IS RECORD (
TARGET_COLUMN TARGET_TABLE.TARGET_COLUMN%TYPE
);
TYPE update_cols_type IS
TABLE OF rt_update_cols INDEX BY PLS_INTEGER;
update_cols_tab update_cols_type;
dml_errors EXCEPTION;
PRAGMA exception_init ( dml_errors,-24381 );
BEGIN
OPEN base_table_cur;
OPEN new_data_cur;
LOOP
FETCH base_table_cur BULK COLLECT INTO base_tab LIMIT 5000;
IF base_table_cur%notfound THEN
DBMS_OUTPUT.PUT_LINE('Nothing to update. Exiting.');
EXIT;
END IF;
FETCH new_data_cur BULK COLLECT INTO new_data_tab LIMIT 5000;
FOR i IN base_tab.first..base_tab.last LOOP
row_id_tab(i) := new_data_tab(i).rowid;
update_cols_tab(i).TARGET_COLUMN := new_data_tab(i).TARGET_COLUMN;
END LOOP;
FORALL i IN base_tab.first..base_tab.last SAVE EXCEPTIONS
UPDATE (SELECT TARGET_COLUMN FROM TARGET_TABLE)
SET row = update_cols_tab(i)
WHERE ROWID = row_id_tab(i);
COMMIT;
EXIT WHEN base_tab.count < 5000; -- changing to 1 didn't help!
END LOOP;
COMMIT;
CLOSE base_table_cur;
CLOSE new_data_cur;
EXCEPTION
WHEN dml_errors THEN
FOR i IN 1..SQL%bulk_exceptions.count LOOP
dbms_output.put_line('Some error occured');
END LOOP;
END;
Where is my mistake? It looks correct to me though.

Answer 1

The problem is this line:
IF base_table_cur%notfound THEN
The cursor meets %NOTFOUND when the number of records found is less than the LIMIT value. So if the last fetch is not exactly 5000 those records won't be processed.
It's a common gotcha for people using BULK COLLECT ... LIMIT for the first time. The solution is to change the exit condition to
EXIT when base_tab.count() = 0;
"I need to ensure, that the base_table_cur is not empty and exit if it is. I'l get an error if it is empty"
The new_data_cur cursor includes the table which is selected in base_table_cur cursor. So I don't think you need the two loops. You need a simple test to see whether the first cursor returns something, then just loop round the second cursor.
I'm not entirely clear on your logic, so I have changed as little as possible to demonstrate the sort of structure I think you need. However, the UPDATE statement looks a little odd, so you may still run into issues.
OPEN base_table_cur;
FETCH base_table_cur BULK COLLECT INTO base_tab LIMIT 1;
if base_table_tab.count = 0 then
DBMS_OUTPUT.PUT_LINE('Nothing to update. Exiting.');
else
OPEN new_data_cur;
LOOP
FETCH new_data_cur BULK COLLECT INTO new_data_tab LIMIT 5000;
exit when new_data_tab.count() = 0;
FOR i IN base_tab.first..base_tab.last LOOP
row_id_tab(i) := new_data_tab(i).rowid;
update_cols_tab(i).TARGET_COLUMN := new_data_tab(i).TARGET_COLUMN;
END LOOP;
FORALL i IN base_tab.first..base_tab.last SAVE EXCEPTIONS
UPDATE (SELECT TARGET_COLUMN FROM TARGET_TABLE)
SET row = update_cols_tab(i)
WHERE ROWID = row_id_tab(i);
END LOOP;
CLOSE new_data_cur;
end if;
COMMIT;
CLOSE base_table_cur;