1. Understanding XHProf
Pinpointing WhyYour 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 likeViews & 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
loadsY 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 (DisableViews 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?