premium guide to online dating sold at 197 pdf - Oracle updating

You do this by specifying values to be matched against one or more columns in the table.Not using a WHERE clause will result in updating all of the rows table. ), how I might cluster rows together that are subject to updates, and what I might do if I just get too many updates to handle. The fastest way to update every row in the table is to rebuild the table from scratch. Case 2 is common in Data Warehouses and overnight batch jobs.

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.

There are 3 runs: RUN 1 RUN 2 RUN 3 ----------------------------------- ----- ----- ----- 1. This makes it a good candidate for hash joins and full scans to out-perform indexed nested loops.

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.

A Hash join may or may not be faster, that's not the point - I could increase the size of the target TEST table to 500M rows and Hash would be slower for sure. The very clear lesson here: don't update bitmap indexed tables in parallel sessions; the only safe parallel method is PARALLEL DML.

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).

Here's the function: CREATE OR REPLACE FUNCTION test_parallel_update ( test_cur IN SYS_REFCURSOR ) RETURN test_num_arr PARALLEL_ENABLE (PARTITION test_cur BY ANY) PIPELINED IS PRAGMA AUTONOMOUS_TRANSACTION; test_rec TEST%ROWTYPE; 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; cnt INTEGER := 0; BEGIN LOOP FETCH test_cur BULK COLLECT INTO pk_tab, fk_tab, fill_tab LIMIT 1000; EXIT WHEN pk_tab. This is a feature of Oracle's parallel-enabled functions; they will apportion the rows of a single Ref Cursor amongst many parallel slaves, with each slave running over a different subset of the input data set. Parallel PL/SQL 28.2 27.2 6.3 Let's see how a Foreign Key constraint affects things. Although not shown here, this effect is magnified with each additional bitmap index.

I spend an inordinate proportion of design time of an ETL system worrying about the relative proportion of rows inserted vs updated.

I want to test on a level playing field and remove special factors that unfairly favour one method, so there are some rules: TEST (Update Source) - 100K rows TEST (Update target) - 10M rows Name Type Name Type ------------------------------ ------------ ------------------------------ ------------ PK NUMBER PK NUMBER FK NUMBER FK NUMBER FILL VARCHAR2(40) FILL VARCHAR2(40) Not many people code this way, but there are some Pro*C programmers out there who are used to Explicit Cursor Loops (OPEN, FETCH and CLOSE commands) and translate these techniques directly to PL/SQL.

The overhead on DML must involve these operations: In this discussion we see a case where the Oracle 11g compression is allegedly "undone" by a update to the table.

The author cites that after updating all of the rows in table, his compress ration is reduced dramatically.

- When you start inserting into this block, data is stored in an uncompressed format (like for uncompressed tables).

Tags: , ,