Oracle Database 11g PL/SQL Programming P2

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These enhancements are briefly reviewed in the following subsections. Chapter 3 covers the SIMPLE_INTEGER datatype. Chapter 4 covers the continue statement. Chapter 6 demonstrates the cross-session PL/SQL function result cache, and both mixed, named, and positional notation calls. Automatic subprogram inlining and the PL/SQL Native Compiler are covered in Chapter 9. Chapter 16 covers web application development and the multiprocess connection pool.

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Nội dung Text: Oracle Database 11g PL/SQL Programming P2

Chapter 1: Oracle PL/SQL Overview 15 can also call the FORMAT_CALL_STACK or FORMAT_ERROR_STACK from the same package to work with thrown exceptions. The following is a simple example: DECLARE local_exception EXCEPTION; FUNCTION nested_local_function RETURN BOOLEAN IS retval BOOLEAN := FALSE; BEGIN RAISE local_exception; RETURN retval; END; BEGIN IF nested_local_function THEN dbms_output.put_line('No raised exception'); END IF; EXCEPTION WHEN others THEN dbms_output.put_line('DBMS_UTILITY.FORMAT_CALL_STACK'); dbms_output.put_line('------------------------------'); dbms_output.put_line(dbms_utility.format_call_stack); dbms_output.put_line('DBMS_UTILITY.FORMAT_ERROR_BACKTRACE'); dbms_output.put_line('-----------------------------------'); dbms_output.put_line(dbms_utility.format_error_backtrace); dbms_output.put_line('DBMS_UTILITY.FORMAT_ERROR_STACK'); dbms_output.put_line('-------------------------------'); dbms_output.put_line(dbms_utility.format_error_stack); END; / This script produces the following output: DBMS_UTILITY.FORMAT_CALL_STACK ------------------------------ ----- PL/SQL Call Stack ----- object line object handle number name 20909240 18 anonymous block DBMS_UTILITY.FORMAT_ERROR_BACKTRACE ----------------------------------- ORA-06512: at line 7 ORA-06512: at line 11 DBMS_UTILITY.FORMAT_ERROR_STACK ------------------------------- ORA-06510: PL/SQL: unhandled user-defined exception You will likely find the FORMAT_ERROR_BACKTRACE the most helpful. It captures the line where the first error occurs at the top, and then moves backward through calls until it arrives at
16 Oracle Database 11g PL/SQL Programming the initial call. Line numbers and program names are displayed together when named blocks are involved in an event stack. Chapter 5 contains more on error management. Wrapping PL/SQL Stored Programs Beginning with Oracle 10g Release 2, the database now supports the ability to wrap, or obfuscate, your PL/SQL stored programs. This is done by using the DBMS_DDL package CREATE_WRAPPED procedure. You use it as follows: BEGIN dbms_ddl.create_wrapped( 'CREATE OR REPLACE FUNCTION hello_world RETURN STRING AS ' ||'BEGIN ' ||' RETURN ''Hello World!''; ' ||'END;'); END; / After creating the function, you can query it by using the following SQL*Plus column formatting and query: SQL> COLUMN message FORMAT A20 HEADING "Message" SQL> SELECT hello_world AS message FROM dual; Message -------------------- Hello World! You can describe the function to inspect its signature and return type: SQL> DESCRIBE hello_world FUNCTION hello_world RETURNS VARCHAR2 Any attempt to inspect its detailed operations will yield an obfuscated result. You can test this by querying stored function implementation in the TEXT column of the USER_SOURCE table, like the following: SQL> COLUMN text FORMAT A80 HEADING "Source Text" SQL> SET PAGESIZE 49999 SQL> SELECT text FROM user_source WHERE name = 'HELLO_WORLD'; The following output is returned: FUNCTION hello_world wrapped a000000 369 abcd . . . et cetera . . . This is a very useful utility to hide the implementation details from prying eyes. We will revisit this in Appendix F.
Chapter 1: Oracle PL/SQL Overview 17 Oracle 11g New Features New PL/SQL features introduced in Oracle 11g include ■ Automatic subprogram inlining ■ A continue statement ■ A cross-session PL/SQL function result cache ■ Dynamic SQL enhancements ■ Mixed, named, and positional notation SQL calls ■ A multiprocess connection pool ■ A PL/SQL Hierarchical Profiler ■ That the PL/SQL Native Compiler now generates native code ■ PL/Scope ■ Regular expression enhancements ■ A SIMPLE_INTEGER datatype ■ Direct sequence calls in SQL statements These enhancements are briefly reviewed in the following subsections. Chapter 3 covers the SIMPLE_INTEGER datatype. Chapter 4 covers the continue statement. Chapter 6 demonstrates the cross-session PL/SQL function result cache, and both mixed, named, and positional notation calls. Automatic subprogram inlining and the PL/SQL Native Compiler are covered in Chapter 9. Chapter 16 covers web application development and the multiprocess connection pool. You will also find more information about the Regular Expression, PL/SQL Hierarchical Profiler, and PL/Scope in Appendixes E, G, and H, respectively. Automatic Subprogram Inlining Inlining a subprogram replaces the call to the external subprogram with a copy of the subprogram. This almost always improves program performance. You could instruct the compiler to inline subprograms by using the PRAGMA INLINE compiler directive in PL/SQL starting with the Oracle 11g Database. You must set the PRAGMA when you have the PLSQL_OPTIMIZE_LEVEL parameter set to 2. Let’s say you have an ADD_NUMBERS stored function in a schema; you can then instruct a PL/SQL program unit to inline the call to the ADD_NUMBERS function. This would be very useful when you call the ADD_NUMBERS function in a loop, as in this example: CREATE OR REPLACE PROCEDURE inline_demo ( a NUMBER , b NUMBER ) IS PRAGMA INLINE(add_numbers,'YES'); BEGIN FOR i IN 1..10000 LOOP
18 Oracle Database 11g PL/SQL Programming dbms_output.put_line(add_function(8,3)); END LOOP; END; / The database automates inlining choices when you set the PLSQL_OPTIMIZE_LEVEL parameter to 3. This generally frees you from identifying when it is appropriate to inline function calls. However, these are only recommendations to the compiler. It is recommended that you let the engine optimize your code during compilation. Continue Statement The CONTINUE statement has finally been added to the PL/SQL language. Some may have mixed emotions. There are opinions that the continue statement leads to less-than-optimal programming, but generally it simplifies loop structures. The CONTINUE statement signals an immediate end to a loop iteration and returns to the first statement in the loop. The following anonymous block illustrates using a continue statement when the loop index is an even number: BEGIN FOR i IN 1..5 LOOP dbms_output.put_line('First statement, index is ['||i||'].'); IF MOD(i,2) = 0 THEN CONTINUE; END IF; dbms_output.put_line('Second statement, index is ['||i||'].'); END LOOP; END; / The MOD function returns a zero when dividing any even number, so the second line is never printed, because the CONTINUE statement aborts the rest of the loop. More on using this command is in Chapter 4. Appendix J covers the MOD function. Cross-Session PL/SQL Function Result Cache The cross-session PL/SQL function result cache is a mechanism to share frequently accessed functions in the SGA between sessions. Prior to the Oracle 11g Database, each call to a function with the same actual parameters, or run-time values, was cached once per session. The only work-around to that functionality required you to code the access methods. You designate either of the following to cache results: RESULT_CACHE clause or RESULT_CACHE RELIES_ON(table_name) The RELIES_ON clause places a limitation on the cached result. Any change to the referenced table invalidates the function, as well as any functions, procedures, or views that depend on the function. The overhead when calling the function for the first time is no different than that from calling a non-cached result. Likewise, the cache will age out of the SGA when it is no longer actively called by sessions.
Chapter 1: Oracle PL/SQL Overview 19 Dynamic SQL Enhancements Dynamic SQL still has two varieties in the Oracle 11g Database. You have Native Dynamic SQL, also known as NDS, and the DBMS_SQL built-in package. Both have been improved in this release. Native Dynamic SQL In Oracle 11g, native dynamic SQL now supports dynamic statements larger than 32KB by accepting CLOB. You access it them in lieu of a SQL statement by using the following syntax: OPEN cursor_name FOR dynamic_string; The dynamic string can be a CHAR, VARCHAR2, or CLOB. It cannot be a Unicode NCHAR or NVARCHAR2. This removes the prior restriction that limited the size of dynamically built strings. The DBMS_SQL Built-in Package Several changes have improved the utility of the DBMS_SQL package. Starting with Oracle 11g, you can now use all NDS-supported datatypes. Also, you can now use the PARSE procedure to work with statements larger than 32KB. This is done by using a CLOB datatype. The CLOB replaces the prior work-around that used a table of VARCHAR2 datatypes (typically VARCHAR2A or VARCHAR2S). Fortunately, the DBMS_SQL package continues to support the work-around, but you should consider moving forward to the better solution. DBMS_SQL has added two new functions: the TO_REFCURSOR and TO_CURSOR_NUMBER functions. They let you transfer reference cursors to cursors and vice versa. There naturally are some words of wisdom on using these. You must open either the cursor or system reference cursor before using them, and after running them you cannot access their old structures. Basically, the code reassigns the interactive reference from the cursor to system reference cursor or from the system reference cursor to the cursor. Last but certainly not least, you can now perform bulk binding operations against user-defined collection types. Collection types can be scalar arrays. You were previously restricted to the types defined by the DBMS_SQL package specification. Mixed Name and Position Notation Calls The Oracle 11g Database brings changes in how name and positional notation work in both SQL and PL/SQL. They actually now work the same way in both SQL and PL/SQL. This fixes a long- standing quirk in the Oracle database. PL/SQL Calls Previously, you had two choices. You could list all the parameters in their positional order or address some to all parameters by named reference. You can now use positional reference, named reference, or a mix of both. The following function will let you experiment with the different approaches. The function accepts three optional parameters and returns the sum of three numbers. CREATE OR REPLACE FUNCTION add_three_numbers ( a NUMBER := 0, b NUMBER := 0, c NUMBER := 0 ) RETURN NUMBER IS BEGIN RETURN a + b + c; END; /
20 Oracle Database 11g PL/SQL Programming The first three subsections show how you call using positional, named, and mixed notation. In these you provide actual parameters for each of the formal parameters defined by the function signature. You can also exclude one or more values because all formal parameters are defined as optional, which means they have default values. This is done in the subsection “Exclusionary Notation.” Positional Notation You call the function using positional notation by BEGIN dbms_output.put_line(add_three_numbers(3,4,5)); END; / Named Notation You call the function using named notation by BEGIN dbms_output.put_line(add_three_numbers(c => 4,b => 5,c => 3)); END; / Mixed Notation You call the function using a mix of both positional and named notation by BEGIN dbms_output.put_line(add_three_numbers(3,c => 4,b => 5)); END; / There is a restriction on mixed notation. All positional notation actual parameters must occur first and in the same order as they are defined by the function signature. You cannot provide a position value after a named value. Exclusionary Notation As mentioned, you can also exclude one or more of the actual parameters when the formal parameters are defined as optional. All parameters in the ADD_THREE_NUMBERS function are optional. The following example passes a value to the first parameter by positional reference, and the third parameter by named reference: BEGIN dbms_output.put_line(add_three_numbers(3,c => 4)); END; / When you opt to not provide an actual parameter, it acts as if you’re passing a null value. This is known as exclusionary notation. This has been the recommendation for years to list the optional variables last in function and procedure signatures. Now, you can exclude one or a couple but not all optional parameters. This is a great improvement, but be careful how you exploit it.
Chapter 1: Oracle PL/SQL Overview 21 SQL Call Notation Previously, you had only one choice. You had to list all the parameters in their positional order because you couldn’t use named reference in SQL. This is fixed in Oracle 11g; now you can call them just as you do from a PL/SQL block. The following demonstrates mixed notation in a SQL call: SELECT add_three_numbers(3,c => 4,b => 5) FROM dual; As in earlier releases you can only call functions that have IN mode–only variables from SQL statements. You cannot call a function from SQL when any of its formal parameters are defined as IN OUT or OUT mode–only variables. This is because you must pass a variable reference when a parameter has an OUT mode. Functions return a reference to OUT mode variables passed as actual parameters. Multiprocess Connection Pool Enterprise JavaBeans (EJBs) just got better with the release of multiprocess connection pooling in the Oracle 11g Database. It is officially Database Resident Connection Pooling (DRCP). This feature lets you manage a more scalable server-side connection pool. Prior to this release you would leverage shared server processes or a multithreaded Java Servlet. The multiprocess connection pool significantly reduces the memory footprint on the database tier, and it boosts the scalability of both the middle and database tiers. A standard database connection requires 4.4MB of real memory; 4MB is allotted for the physical connection and 400KB for the user session. Therefore, 500 dedicated concurrent connections would require approximately 2.2GB of real memory. A shared-server model is more scalable and requires only 600MB of real memory for the same number of concurrent users. Eighty percent of that memory would be managed in Oracle’s Shared Global Area (SGA). Database Resident Connection Pooling scales better and would require only 400MB of real memory. Clearly for web-based applications DRCP is the preferred solution, especially when using OCI8 persistent connections. The behaviors of these models dictate their respective scalability. Figure 1-2 graphically depicts memory use for the three models from 500 to 2,000 concurrent users. FIGURE 1-2 Connection scalability
22 Oracle Database 11g PL/SQL Programming The new feature is delivered by the new DBMS_CONNECTION_POOL built-in package. This package lets you start, stop, and configure connection pooling parameters such as size and time limit. You start the connection pool as the SYS user by using the following command: SQL> EXECUTE DBMS_CONNECTION_POOL.START_POOL(); You must enable your tnsnames.ora file to support the connection to the shared pool. The following enables a shared pool connect descriptor, provided you substitute a correct hostname, domain, and Oracle listener port number: ORCLCP = (DESCRIPTION = (ADDRESS = (PROTOCOL = TCP) (HOST = hostname.domain) (PORT = port_number) ) (CONNECT_DATA = (SERVER = POOLED) (SERVICE_NAME = orcl) ) ) The SERVER key in the connect descriptor directs connections to the connection pooling service. You can only use the connection pool when you have a supported Oracle 11g Database or Oracle 11g Client, though this feature could be subsequently backported. The following error is raised when attempting to connect with an older release client or server library: ERROR: ORA-56606: DRCP: Client version does not support the feature The message is signaled from the server when it fails to create an appropriate socket; it indicates that it is dropping the remote connection pool request. Table 1-2 lists the data dictionary views for auditing connection pools. You can use these to monitor connections or performance characteristics. You stop the connection pool as the SYS user by using the following command: SQL> EXECUTE DBMS_CONNECTION_POOL.STOP_POOL(); View Description DBA_CPOOL_INFO The status, maximum and minimum connections, and idle timeouts are available in this view for each connection pool. V$CPOOL_STAT The number of session requests, the number of times a session that matches a request is found in the pool, and the total wait time per session request are available in this view. V$CPOOL_CC_STATS The connection class level statistics for each instance of the connection pool. TABLE 1-2 Connection Pooling Data Dictionary Views
Chapter 1: Oracle PL/SQL Overview 23 It appears that the initial release will only support a single connection pool. The connection pool name is SYS_DEFAULT_CONNECTION_POOL. You also have three other procedures in the DBMS_CONNECTION_POOL package to manage the connection pool: the ALTER_PARAM(), CONFIGURE_POOL(), and RESTORE_DEFAULTS() procedures. You change a single connection pool parameter with the ALTER_PARAM() procedure. When you want to change more than one to all parameters, you use the CONFIGURE_POOL() procedure. The RESTORE_DEFAULTS() procedure resets all connection pool parameters to their defaults. This new Oracle 11g Database feature certainly improves the scalability of web applications. It is a critical feature that empowers the persistent connection feature introduced in the OCI8 libraries in the Oracle 10g Release 2 database. PL/SQL Hierarchical Profiler The hierarchical profiler delivered in the Oracle 11g Database lets you see how all components in an application perform. This differs from a non-hierarchical (flat) profiler that simply records the time spent in each module. Hierarchical profilers follow the execution cycle from the containing program down to the lowest subprogram. The PL/SQL Hierarchical Profiler does the following: ■ It reports the dynamic execution profile of your PL/SQL program, which is organized by subprogram calls. ■ It divides SQL and PL/SQL execution times and reports them separately. ■ It requires no special source or compile-time preparation, like the PRAGMA required for recommending inlining. ■ It stores results in a set of database tables, which you can use to develop reporting tools or alternatively use the plshprof command-line tool to generate simple HTML reports. The subprogram-level summary includes information about the number of subprogram calls, time spent in subprograms or their subtrees, and detailed information between modules. Appendix G covers how to read and use the PL/SQL Hierarchical Profiler. PL/SQL Native Compiler Generates Native Code PL/SQL Native compilation changes in the Oracle 11g Database. Unlike prior versions where the PL/SQL was translated first into C code and then compiled, you can now compile directly. Execution speed of the final code in some cases is twice as fast or an order of magnitude greater. Oracle recommends that you run all PL/SQL in either NATIVE or INTERPRETED mode. INTERPRETED mode is the database default, and PL/SQL modules are stored as clear text or wrapped text. You can view stored programs by querying the ALL_SOURCE, DBA_SOURCE, or USER_SOURCE data dictionary tables. NATIVE-mode code is compiled into an intermediate form before being reduced to machine-specific code. A copy of the code is also stored in the data dictionary, while the library is positioned in an external directory. You map the physical directory to the virtual directory defined by the PLSQL_NATIVE_LIBRARY_DIR database parameter. Natively compiled code is advantageous when the PL/SQL code run time is slow. This can happen with compute-intensive code, but generally performance delays are caused by SQL statement processing. You should use the new PL/SQL Hierarchical Profiler to determine if there is a significant advantage to support your conversion effort.
24 Oracle Database 11g PL/SQL Programming PL/Scope The PL/Scope is a compiler-driven tool that lets you examine identifiers and their respective behaviors in the Oracle 11g Database. It is disabled by default. You can enable it for the database or session. You should consider enabling it for the session, not the database. You enable it by using the following command: ALTER SESSION SET PLSCOPE_SETTINGS = 'IDENTIFIERS:ALL'; The PL/Scope utility does not collect statistics until you enable it. The statistics let you examine how your programs use identifiers. It should be added to your arsenal of tuning tools. Appendix H gives you a brief introduction to this new feature. Regular Expression Enhancement Oracle 11g Release 1 enhances the functionality of the REGEXP_LIKE and REGEXP_INSTR functions and introduces the REGEXP_COUNT function. Appendix E discusses, reviews, and demonstrates regular expressions using the Oracle 11g Database regular expression functions. SIMPLE_INTEGER Datatype The Oracle 11g Database introduces the SIMPLE_INTEGER. It is a derived subtype of BINARY_ INTEGER, and it has the same range of values. Unlike BINARY_INTEGER, SIMPLE_INTEGER excludes the null value and overflow is truncated. Also, the truncation from overflow does not raise an error. You should use the SIMPLE_INTEGER type if you opt to natively compile your code because it provides significant performance improvements in compiled code. This section has reviewed the Oracle 11g Database new features, or it has referred you to other areas of the book for more information. Clearly, the new features make upgrading very appealing. Direct Sequence Calls in SQL Statements Oracle 11g finally lets you call a sequence with the .nextval or .currval inside SQL commands, which means you can dispense with this: SELECT some_sequence.nextval INTO some_local_variable FROM dual; This book uses the old and new style. The new style is simpler and easier to use. Summary This chapter has reviewed the history, utility, coding basics, and recent features added to the PL/SQL programming language. It has also explained the importance of PL/SQL, and how it can leverage your investment in the Oracle 11g database. You should now see that a combination of SQL and PL/SQL can simplify your external application development projects in languages like Java and PHP.