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Goal Driven Performance Optimization, Peter Zaitsev

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  • 1. Goal Driven Performance Optimization Highload++, October 25-26,2010 Moscow, Russia Peter Zaitsev Percona Inc
  • 2. Goal Driven Performance Optimization What is this all about ? • First step to successful performance optimization is setting right goals • In most cases goals are not set (or unclear) and a lot of resources wasted on not important things • This presentation is about setting the right goals and using them to optimize performance of existing system
  • 3. Goal Driven Performance Optimization When is it Applicable ? • Optimizing Performance for Existing Applications • Can be used with load testing for scaling application and testing new features • A way to implement monitoring and spot problems before users start complain
  • 4. Goal Driven Performance Optimization Understanding Performance • Latency/Response Time – Always Important – Tolerance can be very different • 50ms of Ajax Request • 30minutes for report • Throughtput – Often important for multi-user systems – System can do 1000 transactions/second
  • 5. Goal Driven Performance Optimization Throughput/Latency Relation • Response time tends to increase with throughput – When system overload response time goes to infinity • Call Center analogy – Fewer people servicing calls = better utilization • Same as throughput per person – More people servicing calls = better response time • Calls spend less time waiting in the queue • Classical Performance Optimization Goal – Maximizing Throughput/Utilization while maintaining Response time within a guidelines
  • 6. Goal Driven Performance Optimization Response Time Metrics • Average/Medium/Response Time – Not a good metric for adequate performance – Same as average person temperature in hospital – Can be helpful for historical trending • Maximum Response Time – Good in theory. We want No requests taking longer than X – Hard to work in practice – some requests will take too long • Define Percentile response time – 95% or requests serviced within 500ms – 99% or requests serviced within 1000ms
  • 7. Goal Driven Performance Optimization Alternative Measurments • 95 percentille response time is hard/expensive to compute in SQL – Can use other metrics • APDEX – http://en.wikipedia.org/wiki/Apdex • Portion where response time is within response time – SUM(response_time<0.5)/count(*) – Returning 0.95 Is same as 95% response time of 0.5 sec
  • 8. Goal Driven Performance Optimization Even Response Time • 95% response time goal will allow your system to be non responsive for an hour every day – Ie extremely bad performance when taking backup • You want to ensure there is no stalls/performance dips. • If page loads slow and user presses reload and it loads quickly it is OK – there are always network glitches. • Define your performance goals at short intervals. – Goals should be met at ALL 5 minutes intervals.
  • 9. Goal Driven Performance Optimization Even Response Time math • If you only can work with long intervals you can define stricter performance goals – 99.9% metrics means 2 min slow response will affect it • 86400/1000~=86 (sec) – assuming uniform traffic • The longer response time is OK the larger intervals you can have – 1min allowed response time in 99% cases means 1 hour check interval should be enough
  • 10. Goal Driven Performance Optimization Response Time and an Object • Not all the pages are created Equal • Complexity and User Requirement Differ • Ajax Pop Ups – 50ms • Profile Page Generation – 150ms • Search – 300ms • Site Usage Report – 1000ms
  • 11. Goal Driven Performance Optimization Responses by Type of Client • Human Being – Actual Human waiting and being impatient – Response Time critical • Bots – Some systems have over 80% of bot traffic – Bot response time is less critical • Though should be good enough to be indexed • Interactive Web Services – Can be used to generate pages on other sites – Low Response time is even more critical
  • 12. Goal Driven Performance Optimization Different kinds of Slowness • System “randomly” responds slowly – OK as long as rare enough. – Users will write it off as Internet/computer slowness • Sustained Slowness is bad – Search request which is always slow – User with many friends which is “always” slow • Are these users/cases important ? – Track them separately. They may be invisible with 99% alone. ie Performance per customer – Consider Firing users/Blocking cases otherwise
  • 13. Goal Driven Performance Optimization Where to measure performance • Client Side (the actual data) – http://code.google.com/p/jiffy-web/ – Firebug etc (but only for development) • External Performance Monitoring – Gomez, Keynote etc – Selected pages from selected locations • Web Server Performance Analyses – Focused on one dynamil request response time – http://code.google.com/p/instrumentation-for-php/ – Mk-query-digest; tcprstat
  • 14. Goal Driven Performance Optimization Summary of the Goal • Define 95%, 99% etc response time • For each User Interaction/Class, each application instance/user • Measured/Monitored each 5 minutes • From Front End and Backend observation • Avoiding Performance Holes – Some actions or users which are rare but often slow
  • 15. Goal Driven Performance Optimization Performance Black Swans • Queries can be intrinsically slow or caused to be slow by side load (queueing) • You can ignore outliers only if their impact to system performance is limited. • Discover Such Queries – Mk-query-digest will report outliers by default – Check SHOW PROCESSLIST for never completing queries – Optimize; Build protection to kill overly slow queries.
  • 16. Goal Driven Performance Optimization Production Instrumentation • Many People Instrument Test System – Option to print out Queries/Web Service Requests – Great for Debugging/Testing – Will not show a lot of performance problems • Cold vs hot requests • Contention happening in production • Special User Cases • Run Instrumented App in Production and Store Data – Can instrument only one of Web servers if overhead is large. – Can log only 1% of user sessions if can't handle all data
  • 17. Goal Driven Performance Optimization What to Instrument • Total Response Time • CPU Time • “Wait Time” – Connections/Database Queries – MemCache – Web Services Request – Other Network Requests • Additional Information – Number and Nature of different queries – Hits/Misses for Queries – Options which can affect performance
  • 18. Goal Driven Performance Optimization Where to Store • Plain old log files – Or directly to the database for smaller systems • Load them to the database • Or Hadoop on the larger scale • Generate standard reports • Provide Ad-Hoc way to do deep data analyses
  • 19. Goal Driven Performance Optimization Start from what is most important • Optimize Most important User Interactions first • Pick What case to focus in – Queries which do not meet response time – But not Worse Case Scenario • Unless outliers kill your system • There are always going to be outliers • Do not analyze just queries above response time threshold – It is much easier to reach 95% of 1 second if 50% of the queries are below 500ms.
  • 20. Goal Driven Performance Optimization Benefits of Such Approach • Direct connection to the business goals • High Priority problems targeted first • Focus on real stuff – No guess work like “is my buffer pool hit ratio bad?” or “am I doing too much full table scans ?” – If these there the issues you will find and fix them anyway. • Understandable and predictable result – If MySQL contributes 15% to the response time I can't possibly double performance focusing on MySQL optimization.
  • 21. Goal Driven Performance Optimization Final Notes • Spikes; Special Cases should not be discarded – They are the most interesting/challenging are • Understand what you're trying to achieve – The method is best for optimization of current scale for system already in production. • Check out goal driven performance optimization whitepaper – http://www.percona.com/files/white-papers/goal-driven- performance-optimization.pdf
  • 22. Goal Driven Performance Optimization Thanks for Coming • Questions ? Followup ? – pz@percona.com • Yes, we do MySQL and Web Scaling Consulting – http://www.percona.com • Check out our book – Complete rewrite of 1st edition – Available in Russian Too • And Yes we're hiring – http://www.percona.com/contact/careers/ -22-

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