Choosing Between Native Dynamic SQL and the DBMS_SQL Package

Native Dynamic SQL is Faster than DBMS_SQL

Native dynamic SQL in PL/SQL performs comparably to the performance of static SQL, because the PL/SQL interpreter has built-in support for it. Programs that use native dynamic SQL are much faster than programs that use the DBMS_SQL package. Typically, native dynamic SQL statements perform 1.5 to 3 times better than equivalent DBMS_SQL calls. (Your performance gains may vary depending on your application.)

Native dynamic SQL bundles the statement preparation, binding, and execution steps into a single operation, which minimizes the data copying and procedure call overhead and improves performance.

The DBMS_SQL package is based on a procedural API and incurs high procedure call and data copy overhead. Each time you bind a variable, the DBMS_SQL package copies the PL/SQL bind variable into its space for use during execution. Each time you execute a fetch, the data is copied into the space managed by the DBMS_SQL package and then the fetched data is copied, one column at a time, into the appropriate PL/SQL variables, resulting in substantial overhead.

Performance Tip: Using Bind Variables When using either native dynamic SQL or the DBMS_SQL package, you can improve performance by using bind variables, because bind variables allow Oracle Database to share a single cursor for multiple SQL statements.

For example, the following native dynamic SQL code does not use bind variables:

CREATE OR REPLACE PROCEDURE del_dept ( my_deptno dept.deptno%TYPE) IS

BEGIN

EXECUTE IMMEDIATE 'DELETE FROM dept WHERE deptno = ' || to_char (my_deptno); END;

/

SHOW ERRORS;

For each distinct my_deptno variable, a new cursor is created, causing resource contention and poor performance. Instead, bind my_deptno as a bind variable:

CREATE OR REPLACE PROCEDURE del_dept ( my_deptno dept.deptno%TYPE) IS

BEGIN

EXECUTE IMMEDIATE 'DELETE FROM dept WHERE deptno = :1' USING my_deptno; END;

/

SHOW ERRORS;

6-14 Oracle Database Application Developer's Guide - Fundamentals