Apress.Expert.Oracle.Database.Architecture.9i.and.10g.Programming.Techniques.and.Solutions.Sep.2005

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CHAPTER 1 ■ DEVELOPING SUCCESSFUL ORACLE APPLICATIONS
If you use bind variables, then everyone who submits the same exact query that references
the same object will use the compiled plan from the pool. You will compile your
subroutine once and use it over and over again. This is very efficient and is the way the database
intends you to work. Not only will you use fewer resources (a soft parse is much less
resource intensive), but also you will hold latches for less time and need them less frequently.
This increases your applications’ performance and scalability.
To give you an inkling of how huge a difference the use of bind variables can make performance-wise,
we only need to run a very small test. In this test, we’ll insert some rows into
a table. The simple table we’ll use is as follows:
ops$tkyte@ORA9IR2> drop table t;
Table dropped.
ops$tkyte@ORA9IR2> create table t ( x int );
Table created.
Now we’ll create two very simple stored procedures. They both will insert the numbers
1 through 10,000 into this table; however, the first procedure uses a single SQL statement with
a bind variable:
ops$tkyte@ORA9IR2> create or replace procedure proc1
2 as
3 begin
4 for i in 1 .. 10000
5 loop
6 execute immediate
7 'insert into t values ( :x )' using i;
8 end loop;
9 end;
10 /
Procedure created.
The second procedure constructs a unique SQL statement for each and every row to be
inserted:
ops$tkyte@ORA9IR2> create or replace procedure proc2
2 as
3 begin
4 for i in 1 .. 10000
5 loop
6 execute immediate
7 'insert into t values ( '||i||')';
8 end loop;
9 end;
10 /
Procedure created.
Now, the only difference between the two is that one uses a bind variable and the other
does not. Both are using dynamic SQL (i.e., SQL that is not known until runtime) and the logic
in both is identical. The only change is the use or nonuse of a bind variable.