Understanding XHProf: Pinpointing Why Your Site is Slow and How to Fix It

Transcript

1. Understanding XHProf Pinpointing Why Your Site is Slow and How to Fix It Ezra Gildesgame - Acquia @ezrabg Stanford Drupal Camp 2014
2. The Problem: Slow Websites/Web apps • Unhappy users leave • Severs can’t sustain load
3. Every second counts • http://blog.kissmetrics.com/loading-time/
4. XHProf provides information about execution time • Time spent by the server to generate page sent to the web browser (or API endpoint) • Also measures memory & CPU usage
5. XHProf does not measure: • Time to First Byte (TTFB) • Page render time (happens in the browser) • Other aspects of front-end performance • For page render time, see Chrome Dev tools, YSlow
6. Our goal: Reduce page execution time • Improve user experience • Improve concurrency and efficient use of server resources.
7. Avoid speculation: • “Maybe it’s x” • Wasted time on fruitless investigation • Wasted time on inappropriate remediations • Vague problem descriptions, “Eg, Views is slow”
8. Misconceptions
9. Misconceptions
10. Be smart, m’kay? • Tools like Views & Panels empower you to do inefficient things but aren’t necessarily bad for performance • Views render & query, Panels pane caches are great tools to improve performance
11. Example problem statement • “Entity loads are slow because when we load entities, we load field X which also loads Y data, which spends Z time in the database. Page A loads 1,000 entities of type X.”
12. Use XHProf to • Pinpoint the root cause of performance problems • Develop a surgical remediation plan
13. Key UI Elements • # of function calls • Wall time (Inclusive/exclusive) • Memory usage • CPU time
14. Exclusive/Inclusive • Exclusive: This function only • Inclusive: This function and all child functions
15. CPU Time vs Wall Time • CPU Time: Time spent by the CPU • Wall time: Time including disk I/O • CPU time != Wall time? Likely waiting for disk
16. We may find: • Function called many times unnecessarily • Consider a static cache
17. We may find: • Slow queries • Execute page again with Devel query log, use built-in explain feature
18. We may find: • Many fast queries that stack up
19. We may find
20. We may find • Queries that are quick to execute but slow to assemble
21. We may find: • Excessive entity loads • Excessive calls to memcache set/get
22. What is “excessive” • It depends! Know your app. • Maybe you need that data on that request: Make it less expensive to compute • Maybe you don’t need that data: Don’t compute it
23. We may find: • Page-blocking calls (eg, 3rd-party API requests) • Queue these
24. We may find: • Excessive calls to watchdog() • Notices can slow down your site. • Fix those notices!
25. We may find: • Views/Panels render time - Dig deeper!
26. We may find:
27. Getting started • Brew install xhprof • Install: http://drupal.org/project/xhprof • Alternative: https://github.com/ msonnabaum/xhprof-single-file
28. Avoid dirty runs. • Eliminate menu rebuilds • Disable Devel query log • Disable XDebug - Really. • Test as a non-admin (access control is expensive. We want to observe that.)
29. Know which caches are in place • Views caches (Disable Views caches: https:// gist.github.com/msonnabaum/9671947) • Panels Caches • Other caches
30. Other caches
31. “ZOMG! The site is slow!” • ORLY • Develop a plan to measure and set goals
32. “Slow” Define success with specific performance goals • Execution time on specific page logged in as specific user under specific conditions • Quantify improvements on a per-page basis
33. Example template
34. Case examples
35. Example 1
36. Example: Static Caching in CTools https://drupal.org/node/2049087 • Eliminated ~128,000 calls to t() • Reduced memory footprint • Reduced page execution time by 2 seconds • Simple fix
37. Example: Static caching of node access grants https://drupal.org/comment/8495029 • node_access_grants() never changes within a request • Why compute it multiple times within a request?
38. Example: Avoid unnecessary entity loads https://drupal.org/node/2169099
39. Optimize node access query building https://drupal.org/comment/8516319
40. Questions?