Crotty Plsql Bulk Collect Forall

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April 14, 2004 Next InformationSystems

PL/SQL Bulk Collectionsin Oracle 9i and 10g

Kent Crotty

Burleson Consulting

October 13, 2006




AGENDA

• Performance gains with Bulk Processing

• Array processing with BULK COLLECT andFORALL

• Oracle 10g FORALL improvements.• Error handling.




Top Books on PL/SQL

Dr. Tim Hall Oracle ACEAnd Oracle’s ACE of theYear

John GarmanyA fantastic beginner book onPL/SQL




Bulk Processing

• Supercharge your PL/SQL code with BULKCOLLECTand FORALL

• Working at a table-level instead of the row-level

• Simple and easy to use




PL/SQL Code

• Consists of two types of statementsProcedural (declare, begin, if, while, for …)

SQL (select, insert, update, delete)

•

Oracle has two engines to process that informationPL/SQL EngineSQL Engine

• A Content Switch occurs each time the PL/SQL engine

needs to execute a SQL statement

• Switches are fast but large loops can cause performancedelays




Context Switches

Session PL/SQL

Block

PL/SQL

Block

PL/SQLEngine

Oracle Server

SQL Engine

Procedural

StatementExecutor

SQL Statement

Executor

Data

SQL

PL/SQL

Block




PL/SQL CodeConsider this procedure code

CREATE OR REPLACE PROCEDURE update_price (product_type_in IN product.product_type%TYPE,multiplier_in IN number(2,2) )

ISCURSOR products_cur IS

SELECT product_id, product_priceFROM products WHERE product_type = product_type_in;

BEGINFOR prod_rec IN products_cur LOOPUPDATE products

SET product_price = product_price * multiplier_inWHERE product_id = prod_rec.product_id;

END LOOP;END update_price;




PL/SQL Code

• For each iteration of this loop, there is going to be aconventional bind and a context switch!

• Overhead for these statements can be large

• But there is a solution – Bulk Collections

FOR prod_rec IN products_cur LOOPUPDATE products

SET product_price = product_price * multiplier_inWHERE product_id = prod_rec.product_id;

END LOOP;




Bulk Collection Categories

• SELECT or FETCH statementsBULK COLLECT INTO

• Out-Bind binding

RETURNING clause

• In-Bind binding

FORALL – INSERT, UPDATE, DELETE




SELECT / FETCH statements

Data may be Bulk Collected/Fetched into:

Table.column%TYPE

Record of arrays

Table%ROWTYPE

Cursor%ROWTYPE

Array of records

Nested tables




Products Table

SQL> create table products (2 product_id number,

3 product_name varchar2(15),

4 effective_date date );

Table created.

SQL> begin -- inserting 100000 records into the products table

1 for i in 1 .. 100000 loop

2 insert into products values (i, 'PROD'||to_char(i),sysdate-1);

3 end loop;

4 end;

5 /

PL/SQL procedure successfully completed.

SQL> commit;

Commit complete.




BULK COLLECT clause

• Used in a SELECT statement

• Binds the result set of the query to acollection

• Much less communication between thePL/SQL and SQL engines

• All variables in the INTO clause must be a

collection




BULK COLLECTSET SERVEROUTPUT ON

DECLARE

TYPE prod_tab IS TABLE OF products%ROWTYPE; products_tab prod_tab := prod_tab();

start_time number;

end_time number;

BEGINstart_time := DBMS_UTILITY.get_time;

FOR prod_rec in (SELECT * FROM products

WHERE effective_date BETWEEN sysdate - 2 AND TRUNC(sysdate))

LOOP

products_tab.extend;

products_tab(products_tab.last) := prod_rec;

END LOOP;

end_time := DBMS_UTILITY.get_time;

DBMS_OUTPUT.PUT_LINE(‘Conventional (‘||products_tab.count||’): ’||to_char(end_time-start_time));

Start_time := DBMS_UTILITY.get_time;

SELECT *




BULK COLLECTSQL> /

Conventional (100000): 40

Bulk Collect (100000): 27


Bulk Collect is quite a bitfaster!




BULK COLLECT – Explicit Cursor- FetchDECLARETYPE prod_tab IS TABLE OF products%ROWTYPE;

products_tab prod_tab := prod_tab();

start_time number;

end_time number;

CURSOR products_data IS SELECT * FROM products;

BEGINstart_time := DBMS_UTILITY.get_time;

OPEN products_data;

LOOP

products_tab.extend;

FETCH products_data INTO products_tab(products_tab.last);

IF products_data%NOTFOUND THEN

products_tab.delete(products_tab.last);

EXIT;

END IF;

END LOOP;

CLOSE products_data;


‘ ‘ ’ ’




BULK COLLECTSQL> /

Conventional (100000): 117

Bulk Collect (100000): 14


Bulk Collect is significantly faster – over 8times!




BULK COLLECT - LIMIT

•

Collections are arrays held in memory –massive

collections can eat up all the memory

•

By using the LIMIT clause, we can nowprocess theresult set in chunks

• Explicit cursors must be used with the LIMIT

clause




BULK COLLECT – Explicit Cursor- LIMITDECLARE

TYPE prod_tab IS TABLE OF products%ROWTYPE;

products_tab prod_tab := prod_tab();start_time number;

end_time number;

CURSOR products_data IS SELECT * FROM products;

BEGIN

Start_time := DBMS_UTILITY.get_time;

OPEN products_data;

LOOPFETCH products_data BULK COLLECT INTO products_tab LIMIT 10000;

EXIT WHEN products_data%NOTFOUND;

DBMS_OUTPUT.PUT_LINE('Processed '||to_char(products_tab.count)||' rows');

END LOOP;

CLOSE products_data;


DBMS_OUTPUT.PUT_LINE('Bulk Collect: ‘||to_char(end_time-start_time));

end;Result Set is limited to only 10000 rows – more memoryefficient!

Will the processing be slower because of the LIMIT?




BULK COLLECT – Explicit Cursor- LIMIT

SQL> /

Processed 10000 rows









Processed 10000 rowsBulk Collect: 15


Yes, but only slightly. Still over 8 times better thanconventional!




BULK COLLECT - RETURNING• The RETURNING clause can be used to return

specific columns after a DML statement

• This is referred to as OUT-BINDING

DECLARETYPE prod_tab IS TABLE OF products.product_id%TYPE; products_tab prod_tab := prod_tab();BEGINDELETE FROM productsWHERE product_id > 20000

RETURNING product_id BULK COLLECT INTO products_tab;DBMS_OUTPUT.PUT_LINE('Deleted Product Ids: '||

products_tab.count||' rows');end;SQL> /Deleted Product Ids: 80000 rows





BULK COLLECT Use Considerations

• Use the LIMIT clause to manage

memory requirements

• NO_DATA_FOUND will not be raised

if no records are returned – check

contents to make sure records areretrieved




BULK COLLECT - FORALL

• We have seen BULK COLLECT with the SELECTstatements

• For the INSERT, UPDATE and DELETE

statements there is the FORALL statement

• This is referred to as IN-BINDING




BULK COLLECT – INSERT - FORALLDECLARETYPE prod_tab IS TABLE OF products%ROWTYPE; products_tab prod_tab := prod_tab();start_time number; end_time number;

BEGIN-- Populate a collection - 100000 rowsSELECT * BULK COLLECT INTO products_tab FROM products;

EXECUTE IMMEDIATE 'TRUNCATE TABLE products';Start_time := DBMS_UTILITY.get_time;FOR i in products_tab.first .. products_tab.last LOOPINSERT INTO products (product_id, product_name, effective_date)VALUES (products_tab(i).product_id, products_tab(i).product_name,

products_tab(i).effective_date);END LOOP;end_time := DBMS_UTILITY.get_time;DBMS_OUTPUT.PUT_LINE(‘Conventional Insert: ’||to_char(end_time-start_time));

EXECUTE IMMEDIATE 'TRUNCATE TABLE products';Start_time := DBMS_UTILITY.get_time;FORALL i in products_tab.first .. products_tab.lastINSERT INTO products VALUES products_tab(i);end_time := DBMS_UTILITY.get_time;DBMS_OUTPUT.PUT_LINE(‘Bulk Insert: ’||to_char(end_time-start_time));COMMIT;END;




BULK COLLECT – INSERT - FORALL

SQL> /

Conventional Insert: 686

Bulk Insert: 22


The Bulk Operation is considerablyfaster!




BULK COLLECT – UPDATE - FORALLDECLARETYPE prod_id_tab is TABLE OF products.product_id%TYPE;TYPE prod_tab IS TABLE OF products%ROWTYPE; products_id_tab prod_id_tab := prod_id_tab();

products_tab prod_tab := prod_tab();start_time number;end_time number;BEGIN-- Populate a collection - 10000 rowsFOR i in 1 .. 10000 LOOPproducts_id_tab.extend;products_id_tab(products_id_tab.last) := i+10;

products_tab.extend;products_tab(products_tab.last).product_id := i;END LOOP;

Start_time := DBMS_UTILITY.get_time;FOR i in products_tab.first .. products_tab.last LOOPUPDATE products SET ROW = products_tab(i) -- ROW available in 9.2WHERE product_id = products_tab(i).product_id;

END LOOP;end_time := DBMS_UTILITY.get_time;DBMS_OUTPUT.PUT_LINE('Conventional Update: '||to_char(end_time-start_time));

Start_time := DBMS_UTILITY.get_time;FORALL i in products_tab.first .. products_tab.lastUPDATE products SET ROW = products_tab(i) – ROW available in 9.2 WHERE product_id = products_id_tab(i);end_time := DBMS_UTILITY.get_time;DBMS_OUTPUT.PUT_LINE('Bulk Update: '||to_char(end_time-start_time));END;




BULK COLLECT – UPDATE - FORALL

SQL> /

Conventional Update: 301

Bulk Update: 116


The Bulk Operation is again considerablyfaster!




FORALL Use

•

Only a single DML statement isallowed per FORALL

• In 9i, the binding array must be

sequentially filled• Use SAVE EXCEPTIONS to continue

past errors

•

SQL%BULK_ROWCOUNT returns thenumber of affected rows




The Finer Points

•

Use bulk bind techniques for recurring SQLstatements in a PL/SQL loop.• Bulk bind rules:

• Can be used with any type of collection•

Collection subscripts cannot be expressions• Collections should be densely filled• If error, statement is rolled back. Prior

successful DML statements are not rolled back.

• Bulk Collects• Can be used with implicit or explicit cursors• Collection is always filled sequentially starting

with 1




New in 10g – FORALL Improvements

•

FORALL driving array no longer needs tobe processed in sequential order

• The INDICES OF clause is used toreference the row numbers defined inanother array

• The VALUES OF clause is used toreference the values defined in another

array




New in 10g – FORALL - INDICES

DECLARETYPE prod_id_tab is TABLE OF BOOLEAN INDEX BY PLS_INTEGER;TYPE prod_tab IS TABLE OF products%ROWTYPE;products_id_tab prod_id_tab := prod_id_tab();products_tab prod_tab := prod_tab();BEGINproducts_tab(10).effective_date := sysdate;products_tab(100).effective_date := sysdate + 10;products_tab(1000).effective_date := sysdate + 100;

products_id_tab(10) := TRUE;products_id_tab(100) := TRUE;products_id_tab(1000) := TRUE;

FORALL i IN INDICES OF products_id_tabUPDATE products SET ROW = products_tab(i)WHERE product_id = products_id_tab(i);

END;




New in 10g – FORALL - VALUES

DECLARETYPE prod_id_tab is TABLE OF BOOLEAN INDEX BY PLS_INTEGER;TYPE prod_tab IS TABLE OF products%ROWTYPE;products_id_tab prod_id_tab := prod_id_tab();products_tab prod_tab := prod_tab();BEGINproducts_tab(10).effective_date := sysdate;products_tab(100).effective_date := sysdate + 10;products_tab(1000).effective_date := sysdate + 100;

products_id_tab(100) := 10;products_id_tab(200) := 100;products_id_tab(300) := 1000;

FORALL i IN VALUES OF products_id_tabUPDATE products SET ROW = products_tab(i)WHERE product_id = products_id_tab(i);

END;




FORALL – Error Handling

•

No more FULL rollback in case of anEXCEPTION• SAVE EXCEPTIONS clause• SQL%BULK_EXCEPTIONS – Collection of

records• SQL%BULK_EXCEPTIONS(i).ERROR_INDEX –

stores iteration “i” when exception is raised• SQL%BULK_EXCEPTIONS(i).ERROR_CODE –

stores the Oracle error code• SQL%BULK_EXCEPTIONS.count – returns the

count of the exceptions




Context Switches – Conventional Binds

Session PL/SQL

BlockPL/SQLBlock

PL/SQLEngine

Oracle Server

SQL Engine

Procedural

StatementExecutor

SQL StatementExecutor

Data

SQL

PL/SQL

Block



April 14 2004 Next Information

Context Switches – Bulk Binds

Session PL/SQL

BlockPL/SQLBlock

PL/SQLEngine

Oracle Server

SQL Engine

Procedural

StatementExecutor

SQL StatementExecutor

Data

SQL

PL/SQL

Block

Documents

Crotty Plsql Bulk Collect Forall