Cursor updating table oracle

03-Jun-2018 19:52

But just bear with me, it is the closest PL/SQL equivalent I can make to a third-party ETL Tool such as Data Stage with native parallelism. For brevity, this time we'll just flush the buffer cache and run about 5 minutes worth of indexed reads to cycle the disk cache. Although we are updating only 1% of the rows in the table, those rows are almost perfectly distributed throughout the table.

In this test, we apply the 100K updated rows in Global Temporary Table TEST to permanent table TEST. UPDATE with nested SET subquery 941.4 891.5 31.5 4. RUN 1 RUN 2 ----------------------------------- ----- ----- 1. As a result, we end up updating almost 100% of the blocks.

Wait Total Waited ---------------------------------------- Waited ---------- ------------ db file sequential read 19606 0.37 41.24 db file scattered read 4720 0.52 34.20 SQL*Net message to client 1 0.00 0.00 SQL*Net message from client 1 0.03 0.03 That's a pretty significant difference: the same method (MERGE) is 6-7 times faster when performed as a Hash Join.

Although the number of physical disk blocks and Current Mode Gets are about the same in each test, the Hash Join method performs multi-block reads, resulting in fewer visits to the disk.

You also mentioned that you are updating rows in another table in your cursor's loop. Finally, are you sure that you cannot perform this as one simple SQL statement rather than updating in a cursor's loop?Since Oracle does not yet provide support for record collections in FORALL, we need to use scalar collections, making for long declarations, INTO clauses, and SET clauses. Gaining in popularity due to its combination of brevity and performance, it is primarily used to INSERT and UPDATE in a single statement. Note that I have included a FIRST_ROWS hint to force an indexed nested loops plan. The Deadlock error raised by Method 8 occurred because bitmap indexes are locked at the block-level, not the row level.DECLARE CURSOR rec_cur IS SELECT * FROM test4; TYPE num_tab_t IS TABLE OF NUMBER(38); TYPE vc2_tab_t IS TABLE OF VARCHAR2(4000); pk_tab NUM_TAB_T; fk_tab NUM_TAB_T; fill_tab VC2_TAB_T; BEGIN OPEN rec_cur; LOOP FETCH rec_cur BULK COLLECT INTO pk_tab, fk_tab, fill_tab LIMIT 1000; EXIT WHEN pk_tab. This is to keep the playing field level when comparing to the other methods, which also perform primary key lookups on the target table. 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.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.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).

You also mentioned that you are updating rows in another table in your cursor's loop. Finally, are you sure that you cannot perform this as one simple SQL statement rather than updating in a cursor's loop?Since Oracle does not yet provide support for record collections in FORALL, we need to use scalar collections, making for long declarations, INTO clauses, and SET clauses. Gaining in popularity due to its combination of brevity and performance, it is primarily used to INSERT and UPDATE in a single statement. Note that I have included a FIRST_ROWS hint to force an indexed nested loops plan. The Deadlock error raised by Method 8 occurred because bitmap indexes are locked at the block-level, not the row level.DECLARE CURSOR rec_cur IS SELECT * FROM test4; TYPE num_tab_t IS TABLE OF NUMBER(38); TYPE vc2_tab_t IS TABLE OF VARCHAR2(4000); pk_tab NUM_TAB_T; fk_tab NUM_TAB_T; fill_tab VC2_TAB_T; BEGIN OPEN rec_cur; LOOP FETCH rec_cur BULK COLLECT INTO pk_tab, fk_tab, fill_tab LIMIT 1000; EXIT WHEN pk_tab. This is to keep the playing field level when comparing to the other methods, which also perform primary key lookups on the target table. 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.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.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.