Oracle Server Tuning Accelerator David Scott Intec

Tuning Metaphors Body / Doctor Auto / Mechanic

The Right Solution Fixes the immediate problem Prevents a recurring problem –Fixes the underlying problem Is found and implemented quickly Is cost-effective Is properly documented Has measurable ROI

The Main Thing Is To Keep The Main Thing The Main Thing

Its Slow! - Triage Compared to what? What is Normal? –Do you have benchmarks? What has changed in the environment? –And when? Are you processing the right data? Which part of the system is slow? –most expensive / most used queries Concentrate effort on items with most business impact.

Basic Approach Define the business problem Measure the pain Identify the problem component Find the root cause Investigate and weigh solutions Fix the problem Measure the results

Case Study #1 p1 Define the BUSINESS problem –The GUI is too slow; a loss in productivity $$$ Measure the pain –Screen XYZ in the GUI takes 47 seconds –3000 users use this screen at each login –Most other screens are fine Identify the problem component –Stopwatch timing of XYZ response is 47 seconds –Same SQL query takes 47 seconds –Query identified as culprit

Case Study #1 p2 Find the root cause –Inefficient query Investigate and weigh solutions –Multiple versions of query compared –Results must match original Fix the problem –Replace query in Screen XYZ with tuned version Measure the results –Query returns in 2 seconds –ROI: 3000 users * 45 seconds saved * Avg $10/hour * 260 business days/year = $97,500

Case Study #2 p1 Define the BUSINESS problem –Processing 40M rows exceeds operational window Measure the pain –Users cannot begin sessions until AM –Cost = 2-3 hours overtime for 2 people per day Identify the problem component –Main processing routine takes > 4 hours/day

Case Study #2 p2 Find the root cause –UPDATE of records in main table is not appropriate for increased workload (maximum 1200 rows/second) Investigate and weigh solutions –Used tracing, tkprof, Explain Plan Fix the problem –Rewrite using partitioned staging tables and INSERT /*+APPEND */ Measure the results –Average run is < 2 hours (average 3600 rows/second) –Processing completes before users arrive

Wheres the Wait? Client Application Network Disk CPU Database

Finding Out Whats Wrong Guessing… (from experience, of course) –Old wives tales and Rules of Thumb Trial and Error Statspack Using the V$ Tables –Cache Hit and other ratios –Top SQL (cost, # executions, logical/physical I/O) Explain Plan –Are indexes always good? Are they used? Profiling and Tracing –Autotrace, Event –Wait Events

Investigative Arsenal SQL*Plus Docs –Performance Tuning Guide and Reference Wait event reference –Database Reference Init.ora parameters, V$ view listings Tkprof TOAD, OEM, etc (optional) OS tools: vi, iostat, sar, etc.

Fixing Whats Wrong Change the database configuration: init.ora Statistics –Make better choices, I/O speed is unchanged –Outlines Rewrite –Parallel operations –Hints –More efficient plans Re-architect / Rebuild

Pitfalls Risk: Wasting time chasing a hunch Problem: fixing before finding out! –jumping to conclusions Problem: It cant hurt… –Yes, it can. Problem: Multiple changes at once –Which one fixed it? –Side effects (What else did you break?)

Which Approach, When? Massive problems, entire computer –OS tools, Configuration parameters Entire database is slow, no clues –Statspack, V$ views This query or batch is slow –Autotrace, V$, Tracing, Wait Events

OS Tools Basic observation of resources and processes –top –sar –iostat –ps –ef –ipcs

Configuration Parameters Use AUTO parameters where possible Override only when needed –Have a good reason Remove deprecated parameters Check COMPATIBLE

Parameter Resources Oracle 9i Database Reference Guide, Chapter 1 The usual websites… Oracle Initialization Parameters Pocket Reference by David C. Kreines, OReilly Press

Statspack What is it? How to install it? How to gather data? What is reported? How to report on the data?

Statspack: What is it? System-wide stats and ratios Based on bstat / estat Point-in-time snapshots Automated via DBMS_JOBS Many options and settings

Statspack: Installation Login as a Follow prompts for user, pw, tablespaces Set TIMED_STATISTICS=TRUE Set JOB_QUEUE_PROCESSES=1 or more Total setup time: about 2 minutes!

Statspack: Gather Data Manual –EXEC STATSPACK.SNAP; –Better: SQL> var snap number; SQL> exec :snap := statspack.snap; SQL> print snap Automated (every hour on the hour!) Schedule to capture your workload!

Statspack Content Level >= 0 –General Performance Statistics Level >= 5 –SQL Statement Stats Level >= 6 –SQL Plans and Plan Usage Level >= 7 –Segment Level Stats Level >= 10 –Parent and Child Latches

Statspack: Reports Full Report: spreport.sql –STATS$SNAPSHOT for snapshot info SQL Report: sprepsql.sql –STATS$SQL_SUMMARY for hash info Or just run the reports; the info is displayed!

Statspack Resources Database Performance Tuning Guide and Reference, Chapter 21 –Absolute MUST READ! Websites –Metalink – – Book: –Oracle9i High-Performance Tuning with STATSPACK by Don Burleson

The V$ Views Tons of scripts on the net! Beware of making decisions based on summary information. The info is live – and changes… Interesting views: –V$SQL, V$SQL_TEXT, V$SESSION, V$STAT_NAME, V$SORT_USAGE, V$SESSION_WAIT … and many, many more!

Autotrace Quick plan explanation & basic statistics To setup, see article1/autotrace.html Settings –SET AUTOTRACE ON EXPLAIN –SET AUTOTRACE ON STATISTICS –SET AUTOTRACE ON –SET AUTOTRACE TRACEONLY

Explain Plan explain plan set statement_id = whatever for ; select * from table(dbms_xplan.display); Are the plans what you expect? Full table scans are not always bad See Database Performance Tuning Guide and Reference, Chapter 9

SQL Trace Started in Oracle7 Cryptic but useful information Files written to UDUMP directory Level 1 = Equal to SQL_TRACE=TRUE. Level 4 = SQL_TRACE & bind variables. Level 8 = SQL_TRACE & wait events. Level 12 = Combines levels 4 & 8.

Wait Events Identify where time is spent waiting for work Viewable in V$SESSION_WAIT –join to V$SESSION Written to trace file via event –alter session set events '10046 trace name context forever, level 12'; –alter session set events '10046 trace name context off' ; –exec sys.dbms_system.set_sql_trace_in_session (sid, serial#,TRUE | FALSE);

How to Use Wait Events Modify the process to set the event Run the process (or part of it) Find the trace file Use tkprof to summarize the trace file Find the significant statements Identify the waits Modify the code and/or environment

Using Tkprof tkprof inputfile.trc outputfile Many sorting options –I dont bother… some folks do. To get help, type tkprof w/o parameters Avoid tkprof explain=user/pw –Gives current explain plan, not actual plan Then just vi outputfile

Tkprof Resources Expert Oracle One-On-One by Tom Kyte Database Performance Tuning Guide and Reference, Chapter 10 Every performance book ever written…

10g Changes Everything (Almost) ADDM – Automatic Database Diagnostic Monitor –Statspack, V$, and OEM rolled into 1 place OEM has been expanded To be continued…

Are You Finished? CTD – Compulsive Tuning Disorder Document the solution Calculate the ROI