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Consider three stand-alone procedures, p1, p2 , and p3, such that p2 invokes p1 and p3 invokes p2: benchmark@ORA10G> create or replace procedure p1 2 as 3 begin 4 dbms_output.put_line( 'p1' ); 5 end; 6 / Procedure created.
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benchmark@ORA10G> create or replace procedure p2 2 as 3 begin 4 p1; 5 dbms_output.put_line( 'p2' ); 6 end; 7 / Procedure created. benchmark@ORA10G> create or replace procedure p3 2 as 3 begin 4 p2; 5 dbms_output.put_line( 'p3' ); 6 end; 7 / Procedure created. The dependency chain refers to the fact that p2 depends on p1 and p3 depends on p2. Note that p3 also depends on p1 indirectly. Oracle maintains information in its data dictionary about this dependency chain. Note that this dependency chain may also include schema objects such as tables, views, etc. used by a procedure. Now each time procedure code is changed and recompiled, or a table accessed by the procedure is altered, Oracle makes all the dependent objects invalid in the database. An example will make this clear. Let s first examine the status (valid or invalid) of each of the procedures in the database: benchmark@ORA10G> select object_name, object_type, status 2 from all_objects 3 where object_name in( 'P1', 'P2', 'P3' ) 4 and owner = 'BENCHMARK'; OBJECT_NAME -----------------------------P1 P2 P3 OBJECT_TYPE ------------------PROCEDURE PROCEDURE PROCEDURE STATUS ------VALID VALID VALID
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As expected, all three procedures are valid. Let s now make a simple change to the procedure p1 and recompile it: benchmark@ORA10G> -- modify p1 and recompile it benchmark@ORA10G> create or replace procedure p1 2 as 3 begin 4 dbms_output.put_line( 'p1 modified' ); 5 end; 6 / Procedure created.
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Since p2 and p3 are dependent on procedure p1, Oracle will mark them as invalid in the database, as shown by the following query results: benchmark@ORA10G> select object_name, object_type, status 2 from all_objects 3 where object_name in( 'P1', 'P2', 'P3' ) 4 and owner = 'BENCHMARK'; OBJECT_NAME -----------------------------P1 P2 P3 OBJECT_TYPE ------------------PROCEDURE PROCEDURE PROCEDURE STATUS ------VALID INVALID INVALID
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Note that Oracle automatically tries to recompile an invalid procedure (and all other procedures it is directly or indirectly dependent on) the very first time it is invoked. We can see this in action by first executing p2 and rerunning the query to see the status of each procedure: benchmark@ORA10G> exec p2 p1 modified p2 PL/SQL procedure successfully completed. benchmark@ORA10G> select object_name, object_type, status 2 from all_objects 3 where object_name in( 'P1', 'P2', 'P3' ) 4 and owner = 'BENCHMARK'; OBJECT_NAME -----------------------------P1 P2 P3 OBJECT_TYPE ------------------PROCEDURE PROCEDURE PROCEDURE STATUS ------VALID VALID INVALID
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When we executed p2, Oracle automatically compiled it and ran it. Note, however, that p3 is still invalid. Now, the problem is that if we have a large dependency chain of stand-alone procedures and functions (as may well be the case in a real-life project), then every time a deeply nested procedure is recompiled due to changes, all the procedures depending on it directly or indirectly will become invalid. Oracle will have to recompile each of them as and when they are executed for the first time. Since recompilation is resource-intensive, this can result in performance degradation. Let s see how packages help mitigate this problem. We re-create the same procedures again, only this time, each of them is in its own package (pkg1, pkg2, and pkg3 contain procedures p1, p2, and p3, respectively): benchmark@ORA10G> -- putting the procedures in a package benchmark@ORA10G> create or replace package pkg1 as 2 procedure p1;
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end; /
Package created. benchmark@ORA10G> create or replace package body pkg1 as 2 procedure p1 3 as 4 begin 5 dbms_output.put_line( 'p1' ); 6 end; 7 end; 8 / Package body created. benchmark@ORA10G> create or replace package pkg2 as 2 procedure p2; 3 end; 4 / Package created. benchmark@ORA10G> create or replace package body pkg2 as 2 procedure p2 3 as 4 begin 5 dbms_output.put_line( 'p2' ); 6 pkg1.p1; 7 end; 8 end; 9 / Package body created. benchmark@ORA10G> create or replace package pkg3 as 2 procedure p3; 3 end; 4 / Package created. benchmark@ORA10G> create or replace package body pkg3 as 2 procedure p3 3 as 4 begin
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