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1 The perfect c PLSQL error handler www. syntegris.de

2 www. syntegris.de Blog: svenweller.wordpress.com

3 the perfect c error handler TOPICS Callstack Errorstack optimization levels Error Backtrace UTL_CALLSTACK trace and error logs

4 the perfect c error handler ERROR HANDLER THINK What do we expect from the perfect error handler? How does a typical (g) error handler look like? How does c change the game?

5 the perfect c error handler ERROR HANDLER Questions about PLSQL? Ask this friendly fellow Steven Feuerstein "Handle exceptions at outermost layer to make sure that you present a non-scary feedback to your users, but be ready to add exception handlers in sub-programs and blocks in which you need to log critical application state for later debugging."

6 the perfect c error handler ERROR HANDLER What do we expect from the perfect error handler? Complete information - What: Error stack, Error backtrace - Where: Line, Module, Callstack - Additional Details: Parameters, Current Object No unwanted information No negative performance impact - unless error happens Robust to use, easy to add to code

7 the perfect c error handler ERROR HANDLER How does a typical (g) error handler look like? order_api.create_order(); exception when others then logger.log_error (p_scope=> Create Order ); Exception Section + Logging Framework raise;

8 the perfect c error handler ERROR HANDLER How does c change the game? UTL_CALL_STACK Other c error related enhancements? SQL: VALIDATE_CONVERSION DBMS_PLSQL_CODE_COVERAGE Improved Debugger PRAGMA DEPRECATE

9 PLSQL BASICS capture error messages SQLERRM dbms_utility.format_error_stack dbms_utility.format_call_stack dbms_utility.format_error_backtrace utl_call_stack

10 PLSQL BASICS capture error messages - EXAMPLE declare val number; function divide(a in number, b in number) return number is v_result number; v_result := ab; return v_result; end divide; val := divide(0,0); ORA-07: divisor is equal to zero ORA-0: at line 7 ORA-0: at line No handler

PLSQL BASICS capture error messages - EXAMPLE set serveroutput on declare val number; function divide(a in number, b in number) return number is v_result number;

11 PLSQL BASICS capture error messages - EXAMPLE set serveroutput on declare val number; function divide(a in number, b in number) return number is v_result number; v_result := ab; return v_result; end divide; val := divide(0,0); exception when others then dbms_output.put_line(sqlerrm); ORA-07: divisor is equal to zero SQLERRM

12 PLSQL BASICS capture error messages - EXAMPLE set serveroutput on declare val number; function divide(a in number, b in number) return number is v_result number; v_result := ab; return v_result; end divide; val := divide(0,0); exception when others then dbms_output.put_line(dbms_utility.format_error_stack); ORA-07: divisor is equal to zero ORA-0: at line 7 Error Stack

13 PLSQL BASICS capture error messages - EXAMPLE set serveroutput on declare val number; function divide(a in number, b in number) return number is v_result number; v_result := ab; return v_result; end divide; val := divide(0,0); exception when others then dbms_output.put_line(dbms_utility.format_error_backtrace); ORA-0: at line 7 ORA-0: at line Error Backtrace

14 PLSQL BASICS capture error messages - EXAMPLE set serveroutput on declare val number; function divide(a in number, b in number) return number is v_result number; v_result := ab; return v_result; end divide; val := divide(0,0); exception when others then dbms_output.put_line(dbms_utility.format_call_stack); PLSQL Call Stack object line object handle number name 0x889f0 anonymous block Call Stack

15 PLSQL BASICS STACKS Callstack Which modules have been called so far? Dynamic Callstack Lexical 0 ErrorStack What is the Error (-cascade)? Error Backtrace Where does the Error originate from? Error 0 Errorstack Back- trace 0 Error Backtrace

16 PLSQL BASICS UTL_CALLSTACK Dynamic How big is my call stack Dynamic Callstack Lexical 0 Lexical How many components has my sub module name Error How big is my Error Stack Error 0 Errorstack Back- trace 0 Error Backtrace Backtrace How big is the Error Backtrace

17 PLSQL BASICS.create or replace package body order_api. procedure create_order is. Dynamic. for i in.. loop. create_item;. end loop; 7. exception 8. when others then 9. raise_application_error( , Problem while creating order',true);. Callstack Lexical anonymous_block 0. procedure create_item is. procedure validate is.. raise zero_divide; 7. end validate; validate; 0. exception. when others then. logger.log_error;. raise;. end ;.end order_api;. Error 0 Errorstack Error Backtrace Back- trace 0 order_api.create_order; 7

18 PLSQL BASICS.create or replace package body order_api. procedure create_order is. Dynamic. for i in.. loop. create_item;. end loop; 7. exception 8. when others then 9. raise_application_error( , Problem while creating order,true);. Callstack Lexical anonymous_block 0. procedure create_item is. procedure validate is.. raise zero_divide; 7. end validate; validate; 0. exception. when others then. logger.log_error;. raise;. end ;.end order_api;. Error 0 Errorstack Error Backtrace Back- trace 0 order_api.create_order; 7

19 PLSQL BASICS.create or replace package body order_api. procedure create_order is. Dynamic. for i in.. loop. create_item;. end loop; 7. exception 8. when others then 9. raise_application_error( , Problem while creating order',true);. Callstack Lexical ORDER_API.CREATE_ORDER anonymous_block 0. procedure create_item is. procedure validate is.. raise zero_divide; 7. end validate; validate; 0. exception. when others then. logger.log_error;. raise;. end ;.end order_api;. Error 0 Errorstack Error Backtrace Back- trace 0 order_api.create_order; 7

20 PLSQL BASICS.create or replace package body order_api. procedure create_order is. Dynamic. for i in.. loop. create_item;. end loop; 7. exception 8. when others then 9. raise_application_error( , Problem while creating order',true);. Callstack Lexical ORDER_API.CREATE_ORDER anonymous_block 0. procedure create_item is. procedure validate is.. raise zero_divide; 7. end validate; validate; 0. exception. when others then. logger.log_error;. raise;. end ;.end order_api;. Error 0 Errorstack Error Backtrace Back- trace 0 order_api.create_order; 7

21 PLSQL BASICS.create or replace package body order_api. procedure create_order is. Dynamic. for i in.. loop. create_item;. end loop; 7. exception 8. when others then 9. raise_application_error( , Problem while creating order,true);. Callstack Lexical ORDER_API.CREATE_ORDER anonymous_block 0. procedure create_item is. procedure validate is.. raise zero_divide; 7. end validate; validate; 0. exception. when others then. logger.log_error;. raise;. end ;.end order_api;. Error 0 Errorstack Error Backtrace Back- trace 0 order_api.create_order; 7

22 PLSQL BASICS.create or replace package body order_api. procedure create_order is. Dynamic. for i in.. loop. create_item;. end loop; 7. exception 8. when others then 9. raise_application_error( , Problem while creating order,true);. Callstack Lexical ORDER_API.CREATE_ORDER anonymous_block 0. procedure create_item is. procedure validate is.. raise zero_divide; 7. end validate; validate; 0. exception. when others then. logger.log_error;. raise;. end ;.end order_api;. Error 0 Errorstack Error Backtrace Back- trace 0 order_api.create_order; 7

23 PLSQL BASICS.create or replace package body order_api. procedure create_order is. Dynamic. for i in.. loop. create_item;. end loop; 7. exception 8. when others then 9. raise_application_error( , Problem while creating order,true);. Callstack Lexical ORDER_API.CREATE_ITEM ORDER_API.CREATE_ORDER anonymous_block 0. procedure create_item is. procedure validate is.. raise zero_divide; 7. end validate; validate; 0. exception. when others then. logger.log_error;. raise;. end ;.end order_api;. Error 0 Errorstack Error Backtrace Back- trace 0 order_api.create_order; 7

24 PLSQL BASICS.create or replace package body order_api. procedure create_order is. Dynamic. for i in.. loop. create_item;. end loop; 7. exception 8. when others then 9. raise_application_error( , Problem while creating order,true);. Callstack Lexical ORDER_API.CREATE_ITEM ORDER_API.CREATE_ORDER anonymous_block 0. procedure create_item is. procedure validate is.. raise zero_divide; 7. end validate; validate; 0. exception. when others then. logger.log_error;. raise;. end ;.end order_api;. Error 0 Errorstack Error Backtrace Back- trace 0 order_api.create_order; 7

25 PLSQL BASICS.create or replace package body order_api. procedure create_order is. Dynamic. for i in.. loop. create_item;. end loop; 7. exception 8. when others then 9. raise_application_error( , Problem while creating order,true);. Callstack Lexical ORDER_API.CREATE_ITEM ORDER_API.CREATE_ORDER anonymous_block 0. procedure create_item is. procedure validate is.. raise zero_divide; 7. end validate; validate; 0. exception. when others then. logger.log_error;. raise;. end ;.end order_api;. Error 0 Errorstack Error Backtrace Back- trace 0 order_api.create_order; 7

26 PLSQL BASICS.create or replace package body order_api. procedure create_order is. Dynamic. for i in.. loop. create_item;. end loop; 7. exception 8. when others then 9. raise_application_error( , Problem while creating order',true);. Callstack Lexical ORDER_API.CREATE_ITEM.VALIDATE ORDER_API.CREATE_ITEM ORDER_API.CREATE_ORDER anonymous_block 0. procedure create_item is. procedure validate is.. raise zero_divide; 7. end validate; validate; 0. exception. when others then. logger.log_error;. raise;. end ;.end order_api;. Error 0 Errorstack Error Backtrace Back- trace 0 order_api.create_order; 7

27 PLSQL BASICS.create or replace package body order_api. procedure create_order is. Dynamic. for i in.. loop. create_item;. end loop; 7. exception 8. when others then 9. raise_application_error( , Problem while creating order',true);. Callstack Lexical ORDER_API.CREATE_ITEM.VALIDATE ORDER_API.CREATE_ITEM ORDER_API.CREATE_ORDER anonymous_block 0. procedure create_item is. procedure validate is.. raise zero_divide; 7. end validate; validate; 0. exception. when others then. logger.log_error;. raise;. end ;.end order_api;. Error 0 Errorstack Error Backtrace Back- trace 0 order_api.create_order; 7

28 PLSQL BASICS.create or replace package body order_api. procedure create_order is. Dynamic. for i in.. loop. create_item;. end loop; 7. exception 8. when others then 9. raise_application_error( , Problem while creating order',true);. Callstack Lexical ORDER_API.CREATE_ITEM.VALIDATE ORDER_API.CREATE_ITEM ORDER_API.CREATE_ORDER anonymous_block 0. procedure create_item is. procedure validate is.. raise zero_divide; 7. end validate; validate; 0. exception. when others then. logger.log_error;. raise;. end ;.end order_api;. Error Errorstack 7 divisor is equal to zero Error Backtrace Back- trace ORDER_API order_api.create_order; 7

29 PLSQL BASICS.create or replace package body order_api. procedure create_order is. Dynamic. for i in.. loop. create_item;. end loop; 7. exception 8. when others then 9. raise_application_error( , Problem while creating order',true);. Callstack Lexical ORDER_API.CREATE_ITEM ORDER_API.CREATE_ORDER anonymous_block 0. procedure create_item is. procedure validate is.. raise zero_divide; 7. end validate; validate; 0. exception. when others then. logger.log_error;. raise;. end ;.end order_api;. Error Errorstack 7 divisor is equal to zero at "HR.ORDER_API", line Error Backtrace Back- trace ORDER_API ORDER_API 9 order_api.create_order; 7

30 PLSQL BASICS.create or replace package body order_api. procedure create_order is. Dynamic. for i in.. loop. create_item;. end loop; 7. exception 8. when others then 9. raise_application_error( , Problem while creating order',true);. Callstack Lexical ORDER_API.CREATE_ITEM ORDER_API.CREATE_ORDER anonymous_block 0. procedure create_item is. procedure validate is.. raise zero_divide; 7. end validate; validate; 0. exception. when others then. logger.log_error;. raise;. end ;.end order_api;. Error Errorstack 7 divisor is equal to zero at "HR.ORDER_API", line Error Backtrace Back- trace ORDER_API ORDER_API 9 order_api.create_order; 7

31 PLSQL BASICS.create or replace package body order_api. procedure create_order is. Dynamic. for i in.. loop. create_item;. end loop; 7. exception 8. when others then 9. raise_application_error( , Problem while creating order',true);. Callstack Lexical ORDER_API.CREATE_ITEM ORDER_API.CREATE_ORDER anonymous_block 0. procedure create_item is. procedure validate is.. raise zero_divide; 7. end validate; validate; 0. exception. when others then. logger.log_error;. raise;. end ;.end order_api;. Error Errorstack 7 divisor is equal to zero at "HR.ORDER_API", line at "HR.ORDER_API", line 9 Error Backtrace Back- trace ORDER_API ORDER_API ORDER_API 9 order_api.create_order; 7

32 PLSQL BASICS.create or replace package body order_api. procedure create_order is. Dynamic. for i in.. loop. create_item;. end loop; 7. exception 8. when others then 9. raise_application_error( , Problem while creating order',true);. Callstack Lexical ORDER_API.CREATE_ORDER anonymous_block 0. procedure create_item is. procedure validate is.. raise zero_divide; 7. end validate; validate; 0. exception. when others then. logger.log_error;. raise;. end ;.end order_api;. Error Errorstack 7 divisor is equal to zero at "HR.ORDER_API", line at "HR.ORDER_API", line at "HR.ORDER_API", line 9 Error Backtrace Back- trace ORDER_API ORDER_API ORDER_API 9 ORDER_API order_api.create_order; 7

33 PLSQL BASICS.create or replace package body order_api. procedure create_order is. Dynamic. for i in.. loop. create_item;. end loop; 7. exception 8. when others then 9. raise_application_error( , Problem while creating order',true);. Callstack Lexical ORDER_API.CREATE_ORDER anonymous_block 0. procedure create_item is. procedure validate is.. raise zero_divide; 7. end validate; validate; 0. exception. when others then. logger.log_error;. raise;. end ;.end order_api;. Error Errorstack 000 Problem while creating order 7 divisor is equal to zero at "HR.ORDER_API", line at "HR.ORDER_API", line Error Backtrace Back- trace ORDER_API 9 ORDER_API ORDER_API ORDER_API 9 order_api.create_order; at "HR.ORDER_API", line 9 at "HR.ORDER_API", line 7 ORDER_API

34 PLSQL BASICS.create or replace package body order_api. procedure create_order is. Dynamic. for i in.. loop. create_item;. end loop; 7. exception 8. when others then 9. raise_application_error( , Problem while creating order',true);. Callstack Lexical anonymous_block 0. procedure create_item is. procedure validate is.. raise zero_divide; 7. end validate; validate; 0. exception. when others then. logger.log_error;. raise;. end ;.end order_api;. Error 7 Errorstack 000 Problem while creating order at "HR.ORDER_API", line 9 7 divisor is equal to zero at "HR.ORDER_API", line Error Backtrace Back- trace ORDER_API 9 ORDER_API ORDER_API ORDER_API 9 order_api.create_order; at "HR.ORDER_API", line at "HR.ORDER_API", line 9 7 at "HR.ORDER_API", line ORDER_API NO ENTRY

35 PLSQL BASICS UTL_CALL_STACK Conclusion Callstack Errorstack Error Backtrace utl_call_stack dbms_utility.format_error_stack dbms_utility.format_error_backtrace For capturing call stack, switch to utl_call_stack. As of now Error stack and Error backtrace are easier to use with dbms_utility. Consider how and what to add inside logging framework! Idea: Instead of capturing complete backtrace, only capture the last line.

36 UTL_CALLSTACK USAGE EXAMPLES UTL_CALL_STACK.SUBPROGRAM ( dynamic_depth IN PLS_INTEGER) RETURN UNIT_QUALIFIED_NAME; returns varray() of varchar(k) Where am I? utl_call_stack.concatenate_subprogram( utl_call_stack.subprogram()); Current Submodule ORDER_API.CREATE_ITEM.VALIDATE utl_call_stack.subprogram()(utl_callstack.lexical_depth()+); VALIDATE

37 UTL_CALLSTACK USAGE EXAMPLES - LOGGING FRAMEWORK direct log call logger.log_error(p_scope=> utl_call_stack.subprogram()(utl_call_stack.lexical_depth()+) ); internal log call logger.log_errorc; create or replace package body logger procedure log_errorc is PRAGMA INLINE (log_errorc, 'NO') log_error(p_scope => utl_call_stack.subprogram(+) (utl_callstack.lexical_depth(+)+) ); end log_errorc; Callstack LOGGER.LOG_ERRORC ORDER_API.CREATE_ITEM.VALIDATE ORDER_API.CREATE_ITEM ORDER_API.CREATE_ORDER anonymous_block end logger;

38 UTL_CALLSTACK CONCLUSION + very detailed information + Name of the sub module - Difficult to understand at first - + Compiled Code and Runtime Code can differ (general problem) Usable inside logging framework

39 OPTIMIZATION LEVELS Why is the Line of Error sometimes not correct? In the past SQL Developerdbms_metadata moved the line by because of this: CREATE OR REPLACE procedure myproc as Since 0g: Compiler Code Optimization! Optimisation Level and can move plsql code. The effect is usually very small for optimisation level, but high for level.

OPTIMIZATION LEVELS LEVELS http:stevenfeuersteinonplsql.blogspot.de008plsql-optimization-levels-and-native.html 0. Esoteric for some long-since-passed compatibility issues with release 9 and before.

40 OPTIMIZATION LEVELS LEVELS 0. Esoteric for some long-since-passed compatibility issues with release 9 and before. Basic code generation with debugging data created. Global optimization. Automatic inlining of local procedures Each level builds on the level before. Debugging data is not created above level. Generally, native code generation is independent of optimization level. Native code generation is turned off at levels (and 0) because it interferes with debugging. In other words, PLSQL code compiled at optimization levels 0 and is always interpreted when executed. You should never use level 0. That is a blanket prescription. Certainly no new code should ever require it.

41 OPTIMIZATION LEVELS SETTING THE LEVEL. alter session set PLSQL_OPTIMIZE_LEVEL = ; alter package mypackage compile body;. alter package mypackage compile body plsql_optimize_level = ;. alter package mypackage compile body reuse settings; Info select * from user_plsql_object_settings where object_name = MYPACKAGE ;

42 OPTIMIZATION LEVELS SETTING THE LEVEL SQL Developer TOOLS PREFERENCES DATABASE PLSQL COMPILER LOG

43 OPTIMIZATION LEVELS EXAMPLE A PLSQL Inlining Primer Charles Wetherell

44 OPTIMIZATION LEVELS Manual Inlining with PRAGMA Enforce Inlining PRAGMA INLINE (subprogram, 'YES') Optimisation Level = : Allow Inlining Optimisation Level = : Higher Priority Suppress Inlining PRAGMA INLINE (subprogram, 'NO') Overwrites all YES settings

45 OPTIMIZATION LEVELS REMEMBER PLSQL code optimisation can change the line (level >= ) and the module (level = ) of error (all stacks affected) The only way to find the correct line of error is to compile with a lesser level ( or ). Compile in Prod => PLSQL_OPTIMIZE_LEVEL = Compile in Dev => PLSQL_OPTIMIZE_LEVEL = ( or ) Enable Compiler Warnings! PRO Tipp: Edition Based Redefinition may help to find out correct line of error Use extra edition to run the same code again with a lower optimisation level.

46 ERROR HANDLERS GOOD vs BAD practices

47 GOOD ERROR HANDLERS NO HANDLER order_api.create_order; Gold Standard! Every other exception handler needs to improve the situation compared to having no handler!

48 GOOD ERROR HANDLERS SPECIALIZED EXCEPTION declare r_order order%rowtype; select * into r_order from orders where order_id = ; exception when no_data_found then null; order_api.create_order(); exception when no_data_found then null; Expected errors as soon as possible! Specialized handlers inside modules

49 GOOD ERROR HANDLERS ADD ERROR TO ERROR STACK order_api.create_order(); exception when others then raise_application_error(-000, Problem with creating order, true); rd parameter of raise_application_error adds error to stack. Usefull to capture additional detail information

50 GOOD ERROR HANDLERS LOG AND RERAISE order_api.create_order(); exception when others then logger.log_error( Problem while creating order ); raise; Capture the error and add data to the logged message

51 BAD ERROR HANDLERS DBMS_OUTPUT order_api.create_order(); exception when others then dbms_output.put_line(sqlerrm); raise; DBMS_OUTPUT can be used for debugging, not for permanent error handling SQLERRM looses crucial data, line line of error

52 BAD ERROR HANDLERS SWALLOWED EXCEPTIONS order_api.create_order(); exception when others then null; All calling tools (sql*plus, APEX, Java, ) have ways to handle errors No reason to suppress them at database level! Not always wrong! In very specific circumstances suppressing all errors can be acceptable. But error has to be logged. Comment why breaking the rule!

53 THE WORST ERROR HANDLER DBMS_OUTPUT WITHOUT RAISE order_api.create_order(); exception when others then dbms_output.put_line(sqlerrm); dbms_output + sqlerrm + no raise Special type of hidden swallowed exception

54 BAD ERROR PRACTICES LOG SPAM Antipattern order_api.create_order(); exception when others then logger.log_error; raise; Multiple almost identical entries in log Avoid error handlers that do not capture new information create or replace package body order_api procedure create_order(p_id in number) is for i in.. loop create_item; end loop; exception when others then logger.log_error; raise; procedure create_item is procedure validate is raise zero_divide; exception when others then logger.log_error; raise; end validate; validate; exception when others then logger.log_error; raise; end ; end order_api;

55 BAD ERROR PRACTICES LOG SPAM Antipattern - correction order_api.create_order(); Good but not perfect yet! c does not allow to capture name of submodule in backtrace stack. Message and line of error can be tracked. PLSCOPE could be used to find name of module. But PLSCOPE has compile time, not run time information. create or replace package body order_api procedure create_order(p_id in number) is for i in.. loop create_item; end loop; exception when others then logger.log_error; raise; procedure create_item is procedure validate is raise zero_divide; end validate; validate; end ; end order_api;

56 TRACE AND LOG Catch Module Name create or replace package body order_api procedure create_order is co_module constant varchar(9) := $$PLSQL_UNIT.create_order ; logger.log_trace(p_scope=>co_module, ); do_something; exception when others then logger.log_error(p_scope=>co_module); raise; end order_api; module name constant can be replaced now with utl_call_stack.concatenate_subprogram( utl_call_stack.subprogram()); create or replace package body pkg_example as gc_scope_prefix constant varchar() := lower($$plsql_unit) '.'; procedure todo_proc_name( p_param_todo in varchar) as l_scope logger_logs.scope%type := gc_scope_prefix 'todo_proc_name'; l_params logger.tab_param; logger.append_param(l_params, 'p_param_todo', p_param_todo); logger.log('start', l_scope, null, l_params); -- All calls to logger should pass in the scope... logger.log('end', l_scope); exception when others then logger.log_error('unhandled Exception', l_scope, null, l_params); raise; end todo_proc_name;... example from logger GitHub page end pkg_example;

57 TRACE AND LOG Performance recommendation quick performance create or replace package body order_api procedure create_order(p_id in number) is v_params logger.tab_param; logger.append_param(l_parms, p_id,p_id); logger.log( START,p_params=>v_params); do_something; logger.log( END ); exception when others then logger.log_error( p_message => unhandled exception, p_params => v_params ); raise; end order_api; removal of scope has no noticeable performance effect maximal performance create or replace package body order_api procedure create_order(p_id in number) is $IF $$PLSQL_DEBUG $THEN v_params logger.tab_param; $END $IF $$PLSQL_DEBUG $THEN logger.append_param(l_parms, p_id,p_id); logger.log( START,p_params=>v_params); $END do_something; $IF $$PLSQL_DEBUG $THEN logger.log( END ); $END exception when others then logger.log_error( p_message => unhandled exception $IF $$PLSQL_DEBUG $THEN, p_params => v_params $END ); raise; end order_api; remove trace call completely with compiler directives

58 the perfect c error handler Fazit line of error - bear optimisation levels in mid use utl_call_stack to capture submodule name submodule of error - not reliably know yet, need to ask utl_call_stack.subprogram() less error handlers are better never ever use SQLERRM time to rewrite your error logging framework SQLERRM

59 the perfect c error handler Fazit The perfect PLSQL error handler? Not in c yet! but we are getting closer

60 the perfect c error handler Wishlist for future DB versions a way to inspect optimized code add submodule to backtrace stack use error stack for error messages, backtrace stack to find out where error originates from avoid issues (access error bug) at max backtrace stack depth improved custom error messages to include object information

61 Questions?

The Quest for the perfect PLSQL error handler. Deep Dive into UTL_CALL_STACK. Sven-Uwe Weller.

The Quest for the perfect PLSQL error handler Deep Dive into UTL_CALL_STACK Sven-Uwe Weller www.syntegris.de Sven-Uwe Weller Syntegris CEO, CTO "Design and Development" Oracle Certified Professional,