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Tuning PL/SQL procedures using DBMS_PROFILER

20-August 2009

Tim GormanEvergreen Database Technologies, Inc.

Northern CaliforniaOracle Users Group

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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

User Web server App server DB Server

SQL*Net message from client (wait)

SQL*Net message from client (wait)

CPU (service)

CPU (service)

db file sequential read (wait)

Wait Event

UserResponse

Time

Visual borrowed from Cary Millsap

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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 (O’Reilly & 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

– SQL*Plus script produces summarized “profile report” as HTML

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DBMS_PROFILER

• Files found in “$ORACLE_HOME/rdbms/admin”

• SQL*Plus 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

• SQL*Plus 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”– SQL*Plus script “profiler.sql”

–Queries data generated by runs of the DBMS_PROFILER package

–Generates HTML profiler report as output

– SQL*Plus 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 SQL*Plus script “profiler.sql”

– It will display each session’s RUN-ID, a timestamp, and the RUN-COMMENT

–Choose the appropriate RUN-ID

–Produces spooled output to a file named “profiler_<RUNID>.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

– SQL*Plus script to run the test

– proftest1.tkp

– Output from tkprof <trc-file> <tkp-file> sort=prsela,exeela,fchela explain=<un>/<pwd>

– proftest1_19.html

– proftest1_20.html

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Case Study #1

• No real surprise when you think about it– Using this is faster…

–instr(string, pattern, <pos>, 1)

– …than…

–instr(string, pattern, 1, <occur>)”

– …but THAT MUCH FASTER???

• An easy mistake to make?– 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 when Oracle8 ROWIDs came on the scene– Extremely slow

– Went back to using SUBSTR on ROWID strings

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Case Study #2

• Files:– proftest2.sql

– DDL to create stored procedure and table

– Including use of DBMS_SUPPORT and DBMS_PROFILER

– run_proftest2.sql

– SQL*Plus script to run the test

– proftest2.tkp

– Output from tkprof <trc-file> <tkp-file> sort=prsela,exeela,fchela explain=<un>/<pwd>

– proftest2_1.html

– proftest2_2.html

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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@EvDBT.com