Database & Technology 1 _ Craig Shallahamer _ SQL Elapsed Time Analhysis.pdf

SQL  Elapsed  Time  Analysis  

SQL Elapsed Time

Analysis

Craig A. Shallahamer Founder - OraPub, Inc.

craig@orapub.com

SQL  Elapsed  Time  Analysis  

OraPub is about Oracle performance.

•  OraPub is all about Oracle performance management; systematic and quantitative firefighting and predictive analysis.

•  Web site started in 1995 and the company was founded in 1998 by Craig Shallahamer.

•  OraPub has always been about disseminating Oracle database centric technical information.

•  Consulting, training, books, papers, and products are now being offered.

•  We have been on-site in 24 countries and our resources have been received in probably every country where there are DBAs.

•   Training  •   Unique  Blog  •   Free  Tools  

•   Free  Papers  •   Books  

•   Products  •   Consul8ng  

Resources  

SQL  Elapsed  Time  Analysis  

Short resume...kind of... •  Studies economics, mathematics, and computer science at

university in California, US. •  Started working with Oracle technology in 1989 as a Forms 2.3

developer on Oracle version 5. •  Soon after started performance firefighting...daily! •  Co-found both Oracle’s Core Technology and System

Performance Groups. •  Left Oracle to start OraPub, Inc. in 1998. •  Authored 24 technical papers and worked in 24 countries. •  Authors and teaches his classes Oracle Performance

Firefighting, Adv Oracle Performance Analysis, and Oracle Forecasting & Predictive Analysis.

•  Authored the books, Forecasting Oracle Performance and Oracle Performance Firefighting.

•  Oracle ACE Director. •  Frequent blog contributor: A Wider View

SQL  Elapsed  Time  Analysis  

My two books...

OraPub  discount  code:  IS11  

SQL  Elapsed  Time  Analysis  

One presentation with two parts.

•  “The average” can be misleading.

• Modeling E time leads to insights.

SQL  Elapsed  Time  Analysis  

Working with limited information. SQL ordered by Elapsed DB/Inst: LOOK/LOOK Snaps: 80298-80310!-> Resources reported for PL/SQL code includes the resources used by all SQL! statements called by the code.!-> Total DB CPU (s): 22,800!-> Captured SQL accounts for 109.8% of Total DB CPU!-> SQL reported below exceeded 1.0% of Total DB CPU!! CPU CPU per Elapsd Old! Time (s) Executions Exec (s) %Total Time (s) Physical Reads Hash Value!---------- ------------ ---------- ------ ---------- --------------- ----------! 474.59 38,479 0.01 19.9 479909.89 923,822,548 4166296332!BEGIN pkg_com_unite.st_execute_commune( i_daemon_id => :daemon_id, !i_reload_subult_true_false => :reload_subult_true_false, !i_dump_caches => :dump_caches, i_add_seq2_id => :add_seq2_id, !i_dump_seq2_id => :dump_seq2_id, i_remove_seq2_id => :remove_seq2_id, !i_multi_seq2_chg_true_false => :multi_seq2!

Total  Elapsed  Time  :  479,909.89  seconds  Total  ExecuFons            :  38,479  exec  

SQL  Elapsed  Time  Analysis  

So the average E time is...

E = 479909.89 secs / 38,479 exec! = 12.47 sec/exec!

source:  Init  Hist  Work  2.nb  

SQL  Elapsed  Time  Analysis  

It’s more likely to be like this...

More?  “log  normal”  

SQL  Elapsed  Time  Analysis  

Even more likely...

SQL  Elapsed  Time  Analysis  

What can we do?

We don’t want to mislead others.

We need to truly understand the situation if we are making decisions

based on this information.

SQL  Elapsed  Time  Analysis  

We have a variety of collection options. •  SQL Trace. Valid option.

–  Must have ability to parse the trace files producing E times. –  Can trace on sql_id. –  Must be the production system.

•  Instrument SQL. Valid option. –  May not be practical or possible.

•  Stopwatch. Risky. –  Limited scope and very few samples. –  OK for a specific user situation.

•  Benchmark or Isolated Testing. Very risky. –  If you want real results, you need a real situation (HW, data, arrivals, concurrency).

•  OraPub E Time Collector. Valid, but grabs a core. –  Free tool. OraPub search: “sql elapsed time” –  Gathers at sql_id and plan_hash_value level. –  Grabs and holds a CPU core, ouch!

•  OraPub E Sampler. Valid but not free. –  Un-noticeable impact with same results as tracing or instrumentation! –  Gathers at sql_id level and samples stored in Oracle table. –  Licensed like a box of candy. –  Beta version available for Insync attendees....free! More?  “SQL  sampler”  

SQL  Elapsed  Time  Analysis  

How good is sampled data?

This  is  smoothed  histogram  of  elapsed  Fmes  for  a  specific  sql_id  (query)  collected  using  SQL  Trace,  instrumentaFon,  and  OP  Elapsed  Fme  Sampler  (normal).  Over  a  5  minute  period,  around  80  samples  where  gathered  from  each  collecFon  method.      

All  three  collecFons  methods  produce  the  same  results!  

More?  True  SQL  Elapsed  

SQL  Elapsed  Time  Analysis  

Let’s take a look at some

real data from

real systems.

SQL  Elapsed  Time  Analysis  

#1: Showing all samples.

source:  Aber3129  

Samples : 230!Mean : 57168!Median : 60000!Max : 793996!Collector: OP E Time!

SQL  Elapsed  Time  Analysis  

#1: Showing most samples.

source:  Aber3129  

Samples : 230!Mean : 57168!Median : 60000!Max : 793996!Collector: OP E Time!!

SQL  Elapsed  Time  Analysis  

#2: Showing most samples.

source:  Garret1jqj  

Samples : 368!Mean : 158!Median : 23!Max : 2840!Collector: OP E Time!

SQL  Elapsed  Time  Analysis  

#3: Showing all samples.

source:  Garret8qt  

Samples : 506!Mean : 48!Median : 26!Max : 476!Collector: OP E Time!

SQL  Elapsed  Time  Analysis  

#4: Showing all samples.

source:  Garret  0u2t  

Samples : 179!Mean : 38.72 ms!Median : 38.04 ms!Max : 58.40 ms!Collector: OP E Sampler!

SQL  Elapsed  Time  Analysis  

Experimental Examples.

source:  E  Analysis  1a  (final).nb  

SQL  Elapsed  Time  Analysis  

Conclusions about average E. •  Average elapsed time for a specific SQL

statement can be very misleading. •  Elapsed times are not normally distributed. •  The average elapsed time is not the typical

elapsed time. •  The modes are the typical elapsed times. •  If the mode is not available, then the median

can be used, in some cases. •  If you need to communicate typical elapsed

times, you need to gather real data. More?  “SQL  elapsed”  

SQL  Elapsed  Time  Analysis  

Modeling elapsed time

E = units of work x time per unit

E (time/exec) = WL(work/exec) x RT(time/work)

SQL  Elapsed  Time  Analysis  

Example of elapsed time.

Supposed  a  query  must  access  100,000  logical  IOs  and  each  LIO  takes  0.020ms.  Therefore,  the  elapsed  Fme  will  be  2,000ms  or  2.0  seconds.  

E (ms/exec) = units of work (LIO/exec) X time per work (ms/LIO)!!2000 ms/exec = 100,000 LIO/exec X 0.020 ms/LIO !

SQL  Elapsed  Time  Analysis  

When we tune, WL is reduced. •  SQL tuning fundamentally reduces the

work required to execute a statement. •  Since less work is required then generally,

the elapsed time will decrease! •  If your tuning prowess reduces the work

from 100,000 PIOs to 50,000 PIOs then you can expect the elapsed time to decrease by 50%.

•  But does this really occur in reality? hum...

SQL  Elapsed  Time  Analysis  

Experimental results!

Tuned  SQL  

Stmt  Logical  IO  

Stmt  LIO  Change  

Median  Elapsed  Time  (s)  

Median  Elapsed  Time  (s)  Change  

Samples  

No   355289   -­‐   14.22   -­‐   243  

Yes   161495   -­‐54.55%   5.88   -­‐58.67%   339  

•  CollecFon  interval  was  2  hours.  •  OraPub’s  Elapsed  Time  Sampler  was  used  to  collect  elapsed  Fmes.  •  LIO  numbers  gathered  from  v$sysstat.  •  Time  based  on  Fmestamp  data  type.  

source:  E  Analysis  1a.xlsx,  256  latches  

SQL  Elapsed  Time  Analysis  

Ways to reduce UOW process time. •  There are many ways to reduce the time it

takes to process a single unit of work. •  There are direct methods and indirect

methods. •  Indirect: Because processes share and

compete for resources, when the big issue is resolved, many other issues become less intense.

•  Direct: Tuning Oracle directly reduces the time required to process a piece of work. Hum...

SQL  Elapsed  Time  Analysis  

Experimental results!

CBC  Latches  

Instance  RT  

(ms/lio)  Change  

Instance  WL  

(lio/ms)  

SQL  Stmt  Median  Elapsed  Time  (s)  

Change   Samples  

256   0.03623   -­‐   120   14.224   -­‐   243  

32768   0.00856   -­‐76.36%   227   2.968   -­‐79.13%   399  

•  CollecFon  interval  was  2  hours.  •  OraPub’s  Elapsed  Time  Sampler  was  used  to  collect  elapsed  Fmes.  •  RT  components  gathered  from  v$sysstat,  v$sys_Fme_model,  and  v$system_event.  •  Time  based  on  Fmestamp  data  type.  

source:  E  Analysis  1a.xlsx,  not  tuned  

SQL  Elapsed  Time  Analysis  

This graph shows the work process time.

source:  More  Latches  RT  Compare...xlsx  

-­‐76%  RT  Change  

+96%  WL  Change  

SQL  Elapsed  Time  Analysis  

All situations elapsed times.

SQL  Elapsed  Time  Analysis  

The point? #1 – Average is misleading.

•  It is easy to calculate the average elapsed time...even from Statspack.

•  But saying, “The average elapsed time is X.” will most likely mislead everyone.

•  The median or mode(s) is a much better representation of the typical elapsed times.

•  If you need to communicate typical elapsed times, you need to gather real data.

SQL  Elapsed  Time  Analysis  

The point? #2 – Modeling SQL E. •  Two basic ways to reduce elapsed times:

– Reduce work to be done.

– Reduce time to process each piece of work.

•  SQL statement elapsed time can be simply modeled.

•  SQL statement elapsed time can be anticipated.

SQL  Elapsed  Time  Analysis  

Want to dig deeper? •  Craig’s Blog – A W i d e r V i e w

•  Training from OraPub

–  Oracle Performance Firefighting (I)

–  Adv Oracle Performance Analysis (II)

•  Books

–  Oracle Performance Firefighting (C. Shallahamer)

•  Chapter 9 is FREE to download

Melbourne  &  Perth  in  Q2  2012  

SQL  Elapsed  Time  Analysis  

Thank You!