bulk collect operations performance optimization in plsql

Thursday, 01 May 2008 10:55 Anshuman Ghosh

Bulk Collect operations (performance optimization) in PL/SQL

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This post is relevant in context of bulk operations we do in PLSQL (mostly as part of processes or batch jobs. A practical example is, having a cursor which returns a BIG collection of data, which then has to be processed row by row.

Without using Bulk Collect

The slow (read inefficient) way to do it is to read the cursor row by row, and process the data.

Example-

DECLAREmy_sal emp.sal%TYPE;CURSOR c1 IS SELECT sal FROM emp WHERE job = my_job;

BEGIN...

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OPEN c1; LOOP

FETCH c1 INTO my_sal;EXIT WHEN c1%NOTFOUND;bonus := sal * 0.15; ... further processing (business logic)......

END LOOP;END;

Using Bulk Collect

When using bulk collect, the complete cursor data is fetched into a collection in 1 shot, thereby saving of multiple reads from cursor (and the associated overhead time consumed in context switching between SQL fetches and PLSQL program process).

Example-

PROCEDURE process_all_rowsIS

TYPE employees_collection IS TABLE OF employees%ROWTYPE

INDEX BY PLS_INTEGER;l_employees employees_collection;

BEGINSELECT *BULK COLLECT INTO l_employees

FROM employees;FOR indx IN 1 .. l_employees.COUNT LOOP

my_function_call(l_employees(indx));END LOOP;

END process_all_rows;

Performance metrics

If you wish to have real time metrics of advantages of using bulk_collect, we can do so by timing the processes - once using normal cursor operation and once using bulk collect.

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How to schedule a stored procedure using dbms_scheduler (frequency 3 min )written by Kallepalli Sridhar , May 04, 2008

Hi Anil

Can you please guide me how to use DBMS_SCHEDULER for a stored procedure where the frquency for the program should be for every three min.

Regards SridharVotes: +1


...written by nani , May 26, 2008

Hi ghosh,

Thanks a lot for guidence on bulk collectVotes: +2


THANKSwritten by needhelp , May 30, 2008

Nice explaination regarding BULK COLLECTION. I want some tips regarding how to write query in distributed database..? how many main drawbacks should be keep in mind when writing query.? Because due to it sometime query takes so much time to fetch single record even.

Votes: +1


returing plsqltable as refcursorwritten by venki , June 03, 2008

how an plsql table can be used in select and i want to send it as trhrough refcursor as out parameter can u explain itVotes: +0

...written by Anshuman Ghosh , June 03, 2008

Venki,

In the bulk collect example given above, "l_employees" is indeed a pl/sql table.

TYPE employees_collection IS TABLE OF employeesRO;WTYPE INDEX BY PLS_INTEGER; l_employees employees_collection;

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Last Updated ( Thursday, 01 May 2008 15:21 )

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SELECT * BULK COLLECT INTO l_employees FROM employees;

I shall post a new article on usage of refcursors..Votes: +0

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bulk collect operations performance optimization in plsql

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