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PL/SQL : Stop making the same performance mistakes

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1 PL/SQL : Stop making the same performance mistakes
Tim Hall Oracle ACE Director Oracle ACE of the Year 2006 OakTable Network OCP DBA (7, 8, 8i, 9i, 10g, 11g) OCP Advanced PL/SQL Developer Oracle Database: SQL Certified Expert Books Oracle PL/SQL Tuning Oracle Job Scheduling

2 Stop using PL/SQL… … when you could use SQL.
PL/SQL is a procedural extension to SQL, not a replacement for it. SQL is usually quicker than the PL/SQL alternative. Be an SQL expert who knows some PL/SQL, not the other way round. Learning cool stuff like Analytic Functions will help you avoid writing unnecessary PL/SQL. (setup.sql)

3 Stop using unnecessary PL/SQL
Stop using UTL_FILE to read text files if you can use external tables. (external_table.sql) Stop writing PL/SQL merges if you can use the MERGE statement. (merge.sql) Stop coding multi-table inserts manually. (multitable.sql) Stop using FORALL when you could use DML error logging (DBMS_ERRLOG) to trap failures in DML (dml_el.sql) All use DML, which is easily parallelized.

4 Overview of the PL/SQL Engine
Oracle Server PL/SQL Engine PL/SQL Block Procedural Statement Executor SQL Statement PL/SQL contains procedural and SQL code. Each type of code is processed separately. Switching between code types causes an overhead. The overhead is very noticeable during batch operations. Bulk binds minimize this overhead.

5 Stop Avoiding Bulk-Binds (BULK COLLECT)
Populate collections directly from SQL using BULK COLLECT. (bulk_collect.sql) Collections are held in memory, so watch collection sizes. (bulk_collect_limit.sql) Implicit array processing introduced in 10g. (implicit_array_processing.sql) SELECT * BULK COLLECT INTO l_tab FROM tab1; OPEN c1; LOOP FETCH c1 BULK COLLECT INTO l_tab LIMIT 1000; EXIT WHEN l_tab.count = 0; -- Process chunk. END LOOP; CLOSE c1; FOR cur_rec IN (SELECT * FROM tab1) LOOP -- Process row. END LOOP;

6 Stop Avoiding Bulk-Binds (FORALL)
Bind data in collections into DML using FORALL. (insert_forall.sql) Triggers may not work as you expect. Use INDICIES OF and VALUES OF for sparse collections. Use SQL%BULK_ROWCOUNT to return the number of rows affected by each statement. The SAVE EXCEPTIONS allows bulk operations to complete. Exceptions captured in SQL%BULK_EXCEPTIONS. FORALL i IN l_tab.FIRST .. l_tab.LAST INSERT INTO tab2 VALUES l_tab(i);

7 Stop Using Pass-By-Value (NOCOPY)
By-value: Procedure uses temporary buffer. Copies value back on successful completion. By-reference: Procedure uses original memory location directly. The NOCOPY hint allows OUT and IN OUT parameter to be passed by-reference, rather than by-value. (nocopy.sql) Beware of affect of error handling and parameter aliasing on parameter values. It’s a hint, not a directive, so it can be ignored PROCEDURE myproc (p_tab IN OUT NOCOPY CLOB) IS BEGIN -- Do something. END;

8 Stop Using the Wrong Datatypes
When you use the wrong datatypes, Oracle performs implicit conversions. Datatype conversions take/waste time. Oracle provide multiple numeric datatypes with differing performance characteristics. (numeric_types.sql) Use the appropriate datatype for the job.

9 Quick Points Stop using index searches when you can use ROWIDs.
Stop using custom code when Oracle provide built-in functions. Stop using explicit cursors. Stop avoiding instrumentation in your code. Short-Circuit Evaluations. Logic/Branching order. Stop waiting for requests to complete when you could decouple processes.

10 The End… Questions? References:

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