database technology 1 craig shallahamer sql elapsed time analhysispdf1213

7/26/2019 Database Technology 1 Craig Shallahamer SQL Elapsed Time Analhysispdf1213

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SQL

Elapsed TimeAnalysis

Craig A. ShallahamerFounder - OraPub, Inc.

[email protected]


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OraPub is about Oracle performance.

OraPub is all about Oracle performance

management; systematic and quantitativefirefighting 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.

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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 Oracles 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 Performanceand

Oracle Performance Firefighting.

Oracle ACE Director.

Frequent blog contributor: A Wider View


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My two books...3

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One presentation with two parts.

The average can be misleading.

Modeling E time leads to insights.


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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

,9:'& %&'()*+ ,-.* ; >?@A@B@CD@ )*890+)

,9:'& %E*86F90) ; GDA>?@ *E*8


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So the average E time is...

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

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Its more likely to be like this...

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Even more likely...


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What can we do?

We dont want to mislead others.

We need to truly understand the

situation if we are making decisionsbased on this information.


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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_idand plan_hash_valuelevel.

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_idlevel and samples stored in Oracle table.

Licensed like a box of candy.

Beta version available for Insync attendees....free!H94*I J!"# )'.(&*4L


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How good is sampled data?

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Lets take a look at some

real datafrom

real systems.


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#1: Showing all samples.

)9648*; /7*4G=W@

Samples : 230

Mean : 57168

Median : 60000

Max : 793996

Collector: OP E Time


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#1: Showing most samples.

)9648*; /7*4G=W@

Samples : 230

Mean : 57168

Median : 60000

Max : 793996Collector: OP E Time


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#2: Showing most samples.

)9648*; X'44*:=YQY

Samples : 368Mean : 158

Median : 23

Max : 2840



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)9648*; X'44*:DQ:

Samples : 506Mean : 48

Median : 26

Max : 476



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)9648*; X'44*: B6W:

Samples : 179Mean : 38.72 ms

Median : 38.04 ms

Max : 58.40 ms

Collector: OP E Sampler


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Experimental Examples.

)9648*; % /0'&1)-) =' PO0'&RC07


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Conclusions about average E.

Average elapsed time for a specific SQL

statement can be very misleading. Elapsed times are not normally distributed.

The averageelapsed 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.

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Modeling elapsed time

E =units of work xtime per unit

E (time/exec) =WL(work/exec) xRT(time/work)


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Example of elapsed time.

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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...


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Experimental results!

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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 andcompete for resources, when the big issue isresolved, many other issues become lessintense.

Direct: Tuning Oracle directly reduces thetime required to process a piece of work.Hum...


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Experimental results!

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)9648*; % /0'&1)-) ='CE&)EA 09: :60*+


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This graph shows the work process time.

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All situations elapsed times.


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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.


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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 beanticipated.


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Want to dig deeper?

Craigs Blog A W i d e r V i e w

Trainingfrom OraPub

Oracle Performance Firefighting (I)

Adv Oracle Performance Analysis (II) Books

Oracle Performance Firefighting (C. Shallahamer)

Chapter 9 is FREE to download

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Thank

You!

database technology 1 craig shallahamer sql elapsed time analhysispdf1213

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