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Of course, as you decrease the percentage of blocks updated, the balance will swing in favour of Nested Loops; but this trace demonstrates that MERGE definitely has it's place in high-volume updates.

MERGE /* FIRST_ROWS*/ INTO test USING test2 new ON (= new.pk) WHEN MATCHED THEN UPDATE SET fk = , fill = ------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| ------------------------------------------------------------------------------- | 0 | MERGE STATEMENT | | 95331 | 7261K| 191K (1)| | 1 | MERGE | TEST | | | | | 2 | VIEW | | | | | | 3 | NESTED LOOPS | | 95331 | 8937K| 191K (1)| | 4 | TABLE ACCESS FULL | TEST2 | 95331 | 4468K| 170 (3)| | 5 | TABLE ACCESS BY INDEX ROWID| TEST | 1 | 48 | 2 (0)| | 6 | INDEX UNIQUE SCAN | TEST_PK | 1 | | 1 (0)| ------------------------------------------------------------------------------- call count cpu elapsed disk query current rows ------- ------ -------- ---------- ---------- ---------- ---------- ---------- Parse 1 0.01 0.01 0 4 1 0 Execute 1 57.67 829.77 95323 383225 533245 100000 Fetch 0 0.00 0.00 0 0 0 0 ------- ------ -------- ---------- ---------- ---------- ---------- ---------- total 2 57.68 829.78 95323 383229 533246 100000 Misses in library cache during parse: 1 Optimizer mode: FIRST_ROWS Parsing user id: 140 Rows Row Source Operation ------- --------------------------------------------------- 1 MERGE TEST (cr=383225 pr=95323 pw=0 time=127458586 us) 100000 VIEW (cr=371028 pr=75353 pw=0 time=619853020 us) 100000 NESTED LOOPS (cr=371028 pr=75353 pw=0 time=619653018 us) 100000 TABLE ACCESS FULL TEST2 (cr=750 pr=386 pw=0 time=505310 us) 100000 TABLE ACCESS BY INDEX ROWID TEST (cr=370278 pr=74967 pw=0 time=615942540 us) 100000 INDEX UNIQUE SCAN TEST_PK (cr=200015 pr=227 pw=0 time=4528703 us)(object id 141439) Elapsed times include waiting on following events: Event waited on Times Max.

It's a bit of a kludge, but we can do this in PL/SQL using a Parallel Enable Table Function. COUNT; END LOOP; CLOSE test_cur; COMMIT; PIPE ROW(cnt); RETURN; END; / Note that it receives its data via a Ref Cursor parameter. FK RUN 1 RUN 2 ----------------------------------- ----- ----- 1. A single bitmap index has added around 10% to the overall runtime of PL/SQL solutions, whereas the set-based (SQL-based) solutions run faster than the B-Tree indexes case (above).

The difference is that the Implicit Cursor internally performs bulk fetches, which should be faster than the Explicit Cursor because of the reduced context switches. I generally recommend against it for high-volume updates because the SET sub-query is nested, meaning it is performed once for each row updated. Using BULK COLLECT and FORALL statements is the new de-facto standard for PL/SQL programmers concerned about performance because it reduces context switching overheads between the PL/SQL and SQL engines.

------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| ------------------------------------------------------------------------------- | 0 | MERGE STATEMENT | | 130K| 9921K| 258K (1)| | 1 | MERGE | TEST | | | | | 2 | VIEW | | | | | | 3 | NESTED LOOPS | | 130K| 11M| 258K (1)| | 4 | TABLE ACCESS FULL | TEST2 | 128K| 6032K| 172 (5)| | 5 | TABLE ACCESS BY INDEX ROWID| TEST | 1 | 48 | 2 (0)| | 6 | INDEX UNIQUE SCAN | TEST_PK | 1 | | 1 (0)| --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| TQ |IN-OUT| PQ Distrib | -------------------------------------------------------------------------------------------------------------------- | 0 | MERGE STATEMENT | | 109K| 8325K| 1880 (1)| | | | | 1 | PX COORDINATOR | | | | | | | | | 2 | PX SEND QC (RANDOM) | : TQ10002 | 109K| 10M| 1880 (1)| Q1,02 | P-P | HYBRID (ROW| | 9 | VIEW | | | | | Q1,00 | PCWP | | | 10 | NESTED LOOPS | | 109K| 10M| 1880 (1)| Q1,00 | PCWP | | | 11 | PX BLOCK ITERATOR | | | | | Q1,00 | PCWC | | | 12 | TABLE ACCESS FULL | TEST2 | 107K| 5062K| 2 (0)| Q1,00 | PCWP | | | 13 | TABLE ACCESS BY INDEX ROWID| TEST | 1 | 48 | 0 (0)| Q1,00 | PCWP | | | 14 | INDEX UNIQUE SCAN | TEST_PK | 1 | | 0 (0)| Q1,00 | PCWP | | -------------------------------------------------------------------------------------------------------------------- This is much easier to do with Data Stage than with native PL/SQL. Parallel PL/SQL 25.3 23.8 Surely no comparison of update methods could possibly be complete without a test of Bitmap index maintenance. The other intesting outcome is the differing impact of the bitmap index on SET-based updates vs transactional updates (SQL solutions vs PL/SQL solutions).

The goal is to have several separate sessions applying UPDATE statements at once, rather than using the sometimes restrictive PARALLEL DML alternative. LAST UPDATE test SET fk = fk_tab(i) , fill = fill_tab(i) WHERE pk = pk_tab(i); cnt := cnt pk_tab. In this round, I have removed the Foreign Key used in Round 2, and included a Bitmap index on TEST. PL/SQL solutions seem to incur a penalty when updating bitmap indexed tables.

Thanks,reacha Sorry this was the error that i am getting ORA-06550: line 2, column 29: PL/SQL: ORA-00904: "RETENTION_ID": invalid identifier ORA-06550: line 2, column 14: PL/SQL: SQL Statement ignored ORA-06550: line 11, column 18: PL/SQL: ORA-00904: "B"."RETENTION_ID": invalid identifier ORA-06550: line 9, column 1: in the update statement inside the for loop can't find the table b (alias)the update statement should read like this UPDATE en.agt_name a SET a.emp_num = i.emp_numwhere a.userid = i.retention_id; Ensure retention_id column is exist on the table, as per your DESC result retention_id is does not exist. In your code, you must refer to tarner.nexros by the name you declared for the cursor in your for loop, "i".

So, change your "b"s to "i"s, re-try, and let us know the results.