ORA-01555 error when updating 200 million rows with BULK COLLECT - oracle

Question

I have the following PL/SQL code, which updates one column of each row in a table with about 200 million rows. I use BULK COLLECT to repeatedly fetch 150,000 rows from the table and update the rows. I do a commit after 50,000 updates.
DECLARE
CURSOR jobs_cursor IS
SELECT e.ID, e.PTI, e.CAT, e.JOBNAME, e.JOBDATE, e.WORK_DESCRIPTION
FROM JOB e
WHERE length(e.WORK_DESCRIPTION) > 1000;
TYPE JOBS_TYPE IS TABLE OF jobs_cursor%ROWTYPE;
v_jobs JOBS_TYPE;
fetch_jobs_limit PLS_INTEGER := 150000;
trimmed_work_description VARCHAR2(2000 CHAR);
sub_string_work_description_left VARCHAR2(1000 CHAR);
sub_string_work_description_right VARCHAR2(1000 CHAR);
update_counter NUMBER := 0;
commit_counter NUMBER := 50000;
BEGIN
OPEN jobs_cursor;
LOOP
FETCH jobs_cursor BULK COLLECT INTO v_jobs LIMIT fetch_jobs_limit;
EXIT WHEN v_jobs.COUNT = 0;
FOR idx IN 1..v_jobs.COUNT
LOOP
trimmed_work_description := ' ';
IF v_jobs(idx).WORK_DESCRIPTION IS NOT NULL THEN
trimmed_work_description := TRIM(TRAILING ' ' FROM v_jobs(idx).WORK_DESCRIPTION);
END IF;
IF length(trimmed_work_description) <= 1000 THEN
UPDATE JOBS j SET j.WORK_DESCRIPTION = trimmed_work_description WHERE j.ID = v_jobs(idx).ID;
update_counter := update_counter + 1;
IF mod(update_counter, commit_counter) = 0 THEN
COMMIT;
update_counter := 0;
END IF;
CONTINUE;
ELSIF length(trimmed_work_description) > 1000 THEN
sub_string_work_description_left := SUBSTR(trimmed_work_description, 1, 1000);
sub_string_work_description_right := SUBSTR(trimmed_work_description, 1001, 2000);
END IF;
UPDATE JOBS j SET j.WORK_DESCRIPTION = sub_string_work_description_left WHERE j.ID = v_jobs(idx).ID;
INSERT INTO JOBS j VALUES ("SEQUENCE_JOBS".NEXTVAL, j.PTI, j.CAT, j.JOBNAME, j.JOBDATE, sub_string_work_description_right);
update_counter := update_counter + 1;
IF mod(update_counter, commit_counter) = 0 THEN
COMMIT;
update_counter := 0;
END IF;
END LOOP;
END LOOP;
COMMIT;
CLOSE jobs_cursor;
END;
The code runs for several hours, but then Oracle raises an ORA-01555 - Snapshot too old - Rollback segment number 14 with name xxxx too small.
Could you please tell me what is wrong with my PL/SQL? I already did the Google research and found some threads saying that this error could be avoided by expanding the UNDO table space, however this is not an option in my case. Thus, I need to modify the PL/SQL code.

Answer 1

On first view I don't see any reason why you make the update in a loop, it should be possible with single statements. Would be similar to this (not verified/tested)
update JOBS j SET
WORK_DESCRIPTION = SUBSTR(TRIM(TRAILING ' ' FROM WORK_DESCRIPTION), 1, 1000)
WHERE length(WORK_DESCRIPTION) > 1000;
INSERT INTO JOBS
SELECT SEQUENCE_JOBS.NEXTVAL, j.PTI, j.CAT, j.JOBNAME, j.JOBDATE,
SUBSTR(WORK_DESCRIPTION, 1001, 2000)
FROM JOBS j
WHERE length(TRIM(TRAILING ' ' FROM WORK_DESCRIPTION)) > 1000;