Tuning PLSQL procedures using DBMS_PROFILER

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Northeast Ohio Oracle Users Group
Tuning PL/SQL procedures using DBMS_PROFILER22-M
ay 2009Tim GormanEvergreen Database
Technologies, Inc.
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Agenda

• Overview of tuning tools in Oracle
• Tuning SQL
• SQL Trace
• TKPROF
• Oracle Trace Analyzer
• Method-R Profiler (www.method-r.com)
• Tuning PL/SQL
• DBMS_PROFILER
• Log4plsql
• ???

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Overview of performance tuning

• In order to improve anything, you have to measure
  it
• Is it processing?
• If so, what exactly is it doing?
• Is it waiting on something?
• If so, what exactly is it waiting for?
• Performance tuning is not an art, but a science
• Instrumentation is key

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Understanding where time is spent
Wait Event
User
App server
DB Server
Web server
User Response Time
SQLNet message from client (wait)
CPU (service)
db file sequential read (wait)
CPU (service)
SQLNet message from client (wait)
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Measuring time

• Tracing
• Tracing is the recording of actions performed by
  a program, as they are performed
• Oracle SQL tracing
• Event 10046
• alter session set events 10046 trace name
  context forever, level 8
• exec dbms_support.start_trace
• Optimizing Oracle Performance by Cary Millsap
  and Jeff Holt (OReilly Associates, Sep 2003)
• ISBN 059600527X

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Summarizing tracing data

• Recording every action performed by a program
  generates huge volumes of data to analyze
• Forest and trees
• Look at the trees for diagnosing failures
• Look at the forest to tune performance
• Application profiling
• LOG4PLSQL on http//log4plsql.sourceforge.net/
• C/C programs UNIX prof utility
• Java programs EJP on http//www.sourceforge.net
• Commercial products from http//www.semdesigns.com
  
• profilers for Java, C, C, C, COBOL, other
  languages
• TKPROF for SQL trace data
• Method-R Profiler http//www.method-r.com/software
  /profiler-info
• Profiling is the summarization of trace data

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Profiling

• Using the UNIX prof utility as an example
• Compile a C program using the -p option to
  the cc compiler command
• When compiled/linked program is executed, trace
  information is output to a file specified by
  PROFDIR environment variable (default is
  ./mon.out)
• UNIX prof utility then reads trace information
  and produces a summarized profile report which
  summarizes
• Number of calls to functions
• Amount of time spent in each function

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Profiling

• SQL Trace is another example
• SQL trace is enabled on a session
• All SQL statements executed in that session dump
  trace information to a .trc file in
  USER_DUMP_DEST
• TKPROF program simply reads information in the
  .trc file and summarizes it, displaying
• Execution counts
• CPU and elapsed times
• Number of physical, logical I/O
• Number of rows fetched
• Number of waits and time waited

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What if the problem is not SQL?

• SQL statements perform work in the database
• Summarizing SQL trace info is the best tool for
  tuning SQL
• What if the performance problem was in
• The network? Operating system? DB instance?
• Database wait events can help
• An application program, such as
• Java, C, C, C, COBOL, Fortran, Lisp?
• PL/SQL?

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DBMS_PROFILER

• Introduced with Oracle8i (circa 1998)
• Not installed automatically
• Some files in ORACLE_HOME/rdbms/admin
• Documented in MetaLink note 243755.1
• Download prof.zip from MetaLink
• Oracle PL/SQL Supplied Packages reference on
  DBMS_PROFILER
• Generates trace data in PL/SQL programs
• Trace data saved to tables in database
• SQLPlus script produces summarized profile
  report as HTML

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DBMS_PROFILER

• Files found in ORACLE_HOME/rdbms/admin
• SQLPlus script profload.sql creates the
  package DBMS_PROFILER
• Run once for global setup on database
• Must be performed by SYS user
• Also validates package after creation
• SQLPlus script proftab.sql creates tables to
  store trace data
• Create private sets of tables for each user
• Each user has the three tables and single
  sequence
• Create a global set of tables for all users
• DBA is responsible for granting appropriate
  permissions and creating synonyms for the three
  tables and the single sequence

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DBMS_PROFILER

• Important extra files provided in prof.zip
• SQLPlus script profiler.sql
• Queries data generated by runs of the
  DBMS_PROFILER package
• Generates HTML profiler report as output
• SQLPlus script profgsrc.sql
• Extracts the source of a stored package,
  procedure, or function to an ASCII text file for
  editing
• So that DBMS_PROFILER procedures can be added to
  that source code

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Using DBMS_PROFILER

• Initial setup
• DBMS_PROFILER package has been created by the DBA
  using profload.sql
• developer/user has created the tables using
  proftab.sql
• Add profiler procedures to PL/SQL source
• Procedure START_PROFILER(run-comment)
• Procedure STOP_PROFILER
• Recompile and run the procedure

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Using DBMS_PROFILER

• After running an instrumented PL/SQL program
• Execute the SQLPlus script profiler.sql
• It will display each sessions RUN-ID, a
  timestamp, and the RUN-COMMENT
• Choose the appropriate RUN-ID
• Produces spooled output to a file named
  profiler_ltRUNIDgt.html

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Case Study 1

• A PL/SQL procedure named PROFTEST1
• It queries data from a table
• Stores the data in a comma-separated string
• Then, repeatedly parses and displays each item in
  the string
• There are (at least) two ways to call the INSTR()
  function here
• instr(string, ,, 1, n)
• instr(string, ,, x, 1)
• Which is faster??? Is there a difference?

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Case Study 1

• Files
• proftest1.sql
• DDL to create stored procedure and table
• Including use of DBMS_PROFILER
• run_proftest1.sql
• SQLPlus script to run the test
• proftest1.tkp
• Output from tkprof lttrc-filegt lttkp-filegt
  sortprsela,exeela,fchela explainltungt/ltpwdgt
• proftest1_18.html
• proftest1_19.html

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Case Study 1

• No real surprise when you think about it
• But using instr(string, pattern, m, n) is
  faster
• But THAT MUCH FASTER???
• An easy mistake to make, in hindsight?
• Everything seems obvious in hindsight

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Case Study 2

• Script to estimate the number of rows per block
• Originally written for Oracle v6
• Adapted to Oracle7 without modification
• New ROWID formats in v8 forced changes to the
  script
• Started using DBMS_ROWID package in query
• Extremely slow

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Case Study 2

• DBMS_PROFILER is not recursive
• PL/SQL modules called within instrumented
  procedures are not traced
• PL/SQL modules called within SQL statements are
  not traced
• unless they themselves are instrumented with
  START/STOP_PROFILER calls
• The resolution of replacing DBMS_ROWID package
  calls with SUBSTR was easily determined using SQL
  Trace and TKPROF
• But DBMS_PROFILER pinpointed the exact cause
• Replacing DBMS_ROWID with SUBSTR was just a guess
  with SQL tracing

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Q A?

• Questions? Comments?
• URL http//www.EvDBT.com
• Email Tim_at_EvDBT.com