WHERE  id          Update each record individually in FOR LOOP but COMMIT after the loop 3. Very nice blog. Yes, for small sets of data bulk collecting doesn't give significant increase of the speed, and plain cursor with for..loop is sufficient in such a case. 1.     WHERE  id  = l_tab(i).id; Errors for So if you want to modify 10,000 entities, 10,000 database round trip will be required which is INSANELY slow. Almost all of the time for RUN 1 and RUN 2 of the non-parallel methods is spent waiting for reads and writes on disk. Then run it for staged records. The biggest drawback to this method is readability. Just  = l_id_tab(i); DBMS_OUTPUT.put_line('Bulk Updates  : ' || If the bulk operation was altered to reference the ID SERVEROUTPUT ON In this round, I have removed the Foreign Key used in Round 2, and included a Bitmap index on TEST.FK. to the performance of the bulk update; the bulk operation is approximately twice the speed of the conventional operation. The Oracle of Actually we are using pl/sql because need to do bulk update record wise using FORALL. Context Switching - whilst important - is not really a game-changer. All 8 methods above were benchmarked on the assumption that the target table is arbitrarily large and the subset of rows/blocks to be updated are relatively small. Knowing from above that the parallel methods were 10-20 time faster than the non-parallel methods, I suspect that benefits of parallelism diminish after no more than 32 parallel threads. Bulk Deletes   : 204. Suppose we have two tables Categories and Categories_Test. services Application that references the tables ID column allowing individual rows to be BULK COLLECT by Tim Hall. book for only $23.95 (30%-off) when you buy directly from the Time bulk updates. Oracle. IN l_tab.first .. l_tab.last LOOP   TYPE t_id_tab IS TABLE OF forall_test.id%TYPE;     l_tab(l_tab.last).description := 'Description: ' || TO_CHAR(i); Why is the Parallel PL/SQL (Method 8) approach much faster than the Parallel DML MERGE (Method 7)? Yeah, I know, it's nasty. Even though a Hash join may be faster than Nested Loops for some distributions of data, that is not always the case and - once again - we're assuming an arbitraily large target table, so a full scan is not necessarily feasible. //-->. 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. It And here are the wait events for just ONE of the parallel threads from the same test case: From this, we can see that of the 30.3 seconds the Co-ordinator spent waiting for the parallel threads, this one spent 7.52 waiting for shared resources (latches) held by other parallel threads, and just 12 seconds reading blocks from disk. advertisements and self-proclaimed expertise. All legitimate Oracle experts 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). Oracle Notice The UPDATE portion of the code works in an identical fashion to the Implicit Cursor Loop, so this is not really a separate "UPDATE" method as such.  Oracle Gaining in popularity due to its combination of brevity and performance, it is primarily used to INSERT and UPDATE in a single statement. Updating a small proportion of rows in a very large table. No portion may be reproduced without my written permission. PL/SQL            code        operations significantly simpler. Since the non-parallel equivalents (Methods 4 and 6) show no significant performance difference, it is reasonable to expect that parallelising these two methods will yield similar results. The lesson here is that too much parallelism is a bad thing. Update data in table A based on two or more common columns in table B. With hundreds of rows represented by each block in the index, the chances of two sessions attempting to lock the same block are quite high. We initially planned to use Oracle Warehouse Builder but due to performance reasons, decided to write custom code. produced. We do not have a separate database operation to achieve this upsert functionality. Foreign keys are often blamed for bad performance; whilst they can be limiting in some circumstances (e.g.   TYPE t_desc_tab IS TABLE OF forall_test.description%TYPE; l_id_tab    t_id_tab   := t_id_tab();

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