Database & Technology 1 _ Craig Shallahamer _ SQL Elapsed Time Analhysis.pdf
- 1. SQL Elapsed Time Analysis Craig A. Shallahamer Founder - OraPub, Inc. craig@orapub.com SQL Elapsed Time Analysis
- 2. OraPub is about Oracle performance. • OraPub is all about Oracle performance Resources management; systematic and quantitative firefighting and predictive analysis. • Training • Web site started in 1995 and the company was founded in 1998 by Craig Shallahamer. • Unique Blog • OraPub has always been about disseminating • Free Tools Oracle database centric technical information. • Consulting, training, books, papers, and • Free Papers products are now being offered. • Books • We have been on-site in 24 countries and our resources have been received in probably • Products every country where there are DBAs. • Consul8ng SQL Elapsed Time Analysis
- 3. 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
- 4. My two books... OraPub discount code: IS11 SQL Elapsed Time Analysis
- 5. One presentation with two parts. • “The average” can be misleading. • Modeling E time leads to insights. SQL Elapsed Time Analysis
- 6. 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
- 7. 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
- 8. It’s more likely to be like this... More? “log normal” SQL Elapsed Time Analysis
- 9. Even more likely... SQL Elapsed Time Analysis
- 10. 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
- 11. 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
- 12. 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
- 13. Let’s take a look at some real data from real systems. SQL Elapsed Time Analysis
- 14. #1: Showing all samples. Samples : 230! Mean : 57168! Median : 60000! Max : 793996! Collector: OP E Time! source: Aber3129 SQL Elapsed Time Analysis
- 15. #1: Showing most samples. Samples : 230! Mean : 57168! Median : 60000! Max : 793996! Collector: OP E Time! ! source: Aber3129 SQL Elapsed Time Analysis
- 16. #2: Showing most samples. Samples : 368! Mean : 158! Median : 23! Max : 2840! Collector: OP E Time! source: Garret1jqj SQL Elapsed Time Analysis
- 17. #3: Showing all samples. Samples : 506! Mean : 48! Median : 26! Max : 476! Collector: OP E Time! source: Garret8qt SQL Elapsed Time Analysis
- 18. #4: Showing all samples. Samples : 179! Mean : 38.72 ms! Median : 38.04 ms! Max : 58.40 ms! Collector: OP E Sampler! source: Garret 0u2t SQL Elapsed Time Analysis
- 19. Experimental Examples. source: E Analysis 1a (final).nb SQL Elapsed Time Analysis
- 20. 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
- 21. 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
- 22. 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
- 23. 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
- 24. Experimental results! Median Stmt Median Tuned Stmt LIO Elapsed Logical Elapsed Samples SQL Change Time (s) IO Time (s) Change 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$sysstat. • Time based on Fmestamp data type. source: E Analysis 1a.xlsx, 256 latches SQL Elapsed Time Analysis
- 25. Ways to reduce UOW process time. • There are many ways to reduce the time it takes to process a single unit of work. • There are direct methods and indirect methods. • Indirect: Because processes share and compete for resources, when the big issue is resolved, many other issues become less intense. • Direct: Tuning Oracle directly reduces the time required to process a piece of work. Hum... SQL Elapsed Time Analysis
- 26. Experimental results! SQL Stmt Instance Instance CBC Median RT Change WL Change Samples Latches Elapsed (ms/lio) (lio/ms) Time (s) 256 0.03623 -‐ 120 14.224 -‐ 243 32768 0.00856 -‐76.36% 227 2.968 -‐79.13% 399 • CollecFon interval was 2 hours. • OraPub’s Elapsed Time Sampler was used to collect elapsed Fmes. • RT components gathered from v$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
- 27. This graph shows the work process time. +96% WL Change -‐76% RT Change source: More Latches RT Compare...xlsx SQL Elapsed Time Analysis
- 28. All situations elapsed times. SQL Elapsed Time Analysis
- 29. 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
- 30. 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
- 31. Want to dig deeper? • Craig’s Blog – A W i d e r V i e w • Training from OraPub Melbourne – Oracle Performance Firefighting (I) & Perth in – Adv Oracle Performance Analysis (II) Q2 2012 • Books – Oracle Performance Firefighting (C. Shallahamer) • Chapter 9 is FREE to download SQL Elapsed Time Analysis
- 32. Thank You! SQL Elapsed Time Analysis