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Speed up your backend caches with Heisencache

Speed up your backend caches with Heisencache

Data caching is often over- or ill-used in complex Drupal projects. Until now, there was no good way to capture and log cache events to analyze cache behaviour. Enter Heisencache and reduce the uncertainty.

Frédéric G. MARAND

April 02, 2014
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  1. 1/58 | heisencache | © OSInet Frederic MARAND Speed up

    your backend caches with Heisencache Frédéric G. Marand
  2. 2/58 | heisencache | © OSInet Frederic MARAND Drupal DevDays

    Szeged, 24 30/3/2014 –
  3. 3/58 | heisencache | © OSInet Frederic MARAND CONTEXT MEASURING

    IMPLEMENTATION RESULTS
  4. 4/58 | heisencache | © OSInet Frederic MARAND CONTEXT: perception

    • Front-end dominates • Downloads start after the page is served • Not all sites are equal when it comes to the back/front performance ratio
  5. 5/58 | heisencache | © OSInet Frederic MARAND www.webpagetest.org Major

    press site example: • simple content • below 500 msec backend • tons of extras on page • result: 23 sec front-end time • +/- 50 * backend time CONTEXT: front-end
  6. 6/58 | heisencache | © OSInet Frederic MARAND www.webpagetest.org CONTEXT:

    back-end Major Drupal Commerce site example: • complex backend logic • optimized front-end • +/- 4 * backend time • backend impact = 25%
  7. 7/58 | heisencache | © OSInet Frederic MARAND CONTEXT: battle

    plan • Level1: page caching • Opcode cache • Varnish, CDN • Level 2: storage tuning • MySQL slow queries • MongoDB, Redis, ... • Level 3: cache tuning • On we go... CC BY­NC­ND 2.0 najbo/Flickr
  8. 8/58 | heisencache | © OSInet Frederic MARAND CONTEXT LESS

    DB QUERIES MEANS DATA CACHING Drupal needs caching Cache is a good thing «Cache is king» Steve Souders, author of High-Performance web sites http://fr.slideshare.net/souders/cache-is-king
  9. 9/58 | heisencache | © OSInet Frederic MARAND Photo by

    Alan Light Too much of a good thing is WONDERFUL
  10. 10/58 | heisencache | © OSInet Frederic MARAND (Not that

    kind of good thing) CONTEXT
  11. 11/58 | heisencache | © OSInet Frederic MARAND CONTEXT CACHING

    CAN BE BAD • Memcached speed +/- like good MySQL • Can be worse: clustering network issues • A miss costs more than uncached work
  12. 12/58 | heisencache | © OSInet Frederic MARAND CONTEXT HOW

    DO YOU KNOW WHEN YOU'VE HAD ENOUGH? MEASURE! CC BY­NC­ND 3.0 http://saintgasoline.com
  13. 14/58 | heisencache | © OSInet Frederic MARAND Introducing HEISENCACHE

  14. 15/58 | heisencache | © OSInet Frederic MARAND CONTEXT MEASURING

    IMPLEMENTATION RESULTS
  15. 16/58 | heisencache | © OSInet Frederic MARAND MEASURING WHY

    HEISENCACHE? CC BY 3.0 Gerhard Hund
  16. 17/58 | heisencache | © OSInet Frederic MARAND MEASURING •

    Reduce uncertainty • Minimize observer impact • Don't push the analogy too far
  17. 18/58 | heisencache | © OSInet Frederic MARAND MEASURING THE

    COST OF MEASUREMENT • Observer code runs within Drupal • Needs to be invoked more CPU → • Needs to store data more I/O →
  18. 19/58 | heisencache | © OSInet Frederic MARAND MEASURING CACHING

    BEHAVIOUR vs. LOAD PROFILE
  19. 20/58 | heisencache | © OSInet Frederic MARAND • Instant

    peaks for top content • Fast decay • TTL works wonders • Long tail issues MEASURING: Sports site CC BY 2.0 Ronnie Macdonald
  20. 21/58 | heisencache | © OSInet Frederic MARAND • Many

    content pieces • Few repeat hits • Complex cache policy • Avoid caching some data • Preserve cache memory for selected content MEASURING: Regional TV
  21. 22/58 | heisencache | © OSInet Frederic MARAND MEASURING OBSERVE

    CACHE IN PRODUCTION
  22. 23/58 | heisencache | © OSInet Frederic MARAND MEASURING in

    production • Precision vs. velocity? • Performance module • Cannot write to the DB in real-time • Cached pages • Observing bootstrap
  23. 24/58 | heisencache | © OSInet Frederic MARAND CONTEXT MEASURING

    IMPLEMENTATION RESULTS
  24. 25/58 | heisencache | © OSInet Frederic MARAND IMPLEMENTATION: early

    hits DRUPAL 7 BOOT SEQUENCE • Page cycle: index.php → drupal_bootstrap() • Configuration, Page Cache, DB, Variables, Session, Page Header, Language, Full • Cache handlers declaration: settings.php
  25. 26/58 | heisencache | © OSInet Frederic MARAND IMPLEMENTATION: early

    hits FIRST POSSIBLE CACHE HITS • Exotic: sites.php, settings.php, drupal_settings_initialize() CC BY­SA 3.0 Mdk572/Wikimedia Commons • Normally not (phew...)
  26. 28/58 | heisencache | © OSInet Frederic MARAND IMPLEMENTATION: early

    hits CATCHING EARLY HITS • _drupal_bootstrap_page_cache(): 2nd boot phase • So? Start during 1st bootstrap phase • No module system, no DB as this point • When measuring a cached page hit, don't open the DB
  27. 29/58 | heisencache | © OSInet Frederic MARAND IMPLEMENTATION: early

    hits SOLUTION Use a standalone event dispatching system
  28. 30/58 | heisencache | © OSInet Frederic MARAND IMPLEMENTATION: operation

    IDEAS • Doctrine, NodeJS and Symfony event systems • Use dependency injection, but no DIC (on D7)
  29. 31/58 | heisencache | © OSInet Frederic MARAND IMPLEMENTATION: operation

    BONUS • Composer for deployment – Before hooks, so no composer_manager • Easy unit testing decent code → coverage
  30. 32/58 | heisencache | © OSInet Frederic MARAND IMPLEMENTATION: coverage

  31. 33/58 | heisencache | © OSInet Frederic MARAND IMPLEMENTATION: cache

    driver DECORATOR PATTERN • Inspiration: authcache • Read existing cache configuration • Save it, declare as the sole cache provider • Handle requests per the original configuration, but enhance the service
  32. 34/58 | heisencache | © OSInet Frederic MARAND IMPLEMENTATION: cache

    driver EMIT EVENTS AROUND ALL OPERATIONS • Configuration • Initialization • Cache operations • …and page termination
  33. 35/58 | heisencache | © OSInet Frederic MARAND IMPLEMENTATION: late

    hits CATCHING LATE HITS 1/2 • hook_exit ? Lots of code after that @see drupal_page_footer() • Catching page caching ? – not triggered on AJAX callbacks @see ajax_deliver() – poormancron can run lots of code after that
  34. 36/58 | heisencache | © OSInet Frederic MARAND IMPLEMENTATION: late

    hits CATCHING LATE HITS 2/2 • Catching the session commit? – Only if a session was started – Dirty interactions – Session regeneration • => Shutdown function stack
  35. 37/58 | heisencache | © OSInet Frederic MARAND NEEDS •

    minimize I/O load aim for #writes <= 1 → • «Fingers crossed»-inspired strategy – Keep data in memory during the page lifecycle – Write it at end of page IMPLEMENTATION: storing data
  36. 38/58 | heisencache | © OSInet Frederic MARAND IMPLEMENTATION: storing

    data CHALLENGES • Writing after the last possible cache operation • Write while classes are still available • Passing information within an event-oriented procedural code base
  37. 39/58 | heisencache | © OSInet Frederic MARAND IMPLEMENTATION: events

    EventEmitter (à la Node) • narrowcast events created by sources • subscribers add/remove events on the fly – can further tighten narrowcasting
  38. 40/58 | heisencache | © OSInet Frederic MARAND IMPLEMENTATION: events

    EventSubscriberInterface • Doctrine/Symfony • + (add | remove)Event() EventSourceInterface • Define events a source can emit • Base source of events: Cache API
  39. 41/58 | heisencache | © OSInet Frederic MARAND IMPLEMENTATION: events

    SYNTHETIC EVENTS • API Limitations: post-operation cache events do not get the operation settings • Enable immediate event reconciliation • Event susbcribers can also be sources
  40. 42/58 | heisencache | © OSInet Frederic MARAND IMPLEMENTATION: events

    SYNTHETIC EVENT EXAMPLES • MissSubscriber: miss info for Cache::get() • PerformanceSubscriber: timing info for all ops • WriteSubscriber: single event for write and delete ops
  41. 43/58 | heisencache | © OSInet Frederic MARAND IMPLEMENTATION: setup

    heisencache.inc PLUGIN BOOTSTRAP • wrap $conf, create Config and EventEmitter instances • register a Drupal shutdown handler emitting an onShutdown event • setup the cache override, include settings.heisencache.inc
  42. 44/58 | heisencache | © OSInet Frederic MARAND IMPLEMENTATION: setup

    settings.heisencache.inc CONFIGURATION • Retrieve the EventEmitter from Config instance • Create EventSubscriber instances as chosen • Register them on chosen events • DebugSubscriber listen to all events – not in production ! • Don't forget to include a WriterSubscriber
  43. 45/58 | heisencache | © OSInet Frederic MARAND IMPLEMENTATION: extending

    HEISENCACHE IS A CODER TOOL
  44. 46/58 | heisencache | © OSInet Frederic MARAND IMPLEMENTATION: extending

    EASY TO EXTEND : • Write additional EventSubscriber classes • Add them to your configuration ALREADY EXTENDED : • WriterSubscriber is a user contribution
  45. 47/58 | heisencache | © OSInet Frederic MARAND IMPLEMENTATION: extending

    MOST TYPICAL • Create new subscriber for custom conditions • Create new writer classes • Target alternate stores for speed and ease • MongoDB • K/V or data structure store (Redis) • Message queue (Beanstalkd, RabbitMQ, ZeroMQ, etc)
  46. 48/58 | heisencache | © OSInet Frederic MARAND IMPLEMENTATION: extending

    CREATING A WRITER CLASS • Extend BaseWriterSubscriber • or implement BaseEventSubscriber yourself • Handle the onShutdown event • write $this->history – where you want – how you want
  47. 49/58 | heisencache | © OSInet Frederic MARAND IMPLEMENTATION: extending

    EXISTING WRITER CLASSES • WatchdogWriterSubscriber {watchdog} → • SqlWriterSubscriber specific table →
  48. 50/58 | heisencache | © OSInet Frederic MARAND IMPLEMENTATION: UI

    • ROLL YOUR OWN! • Use WatchdogSubscriber data ‒ Just use admin/reports/dblog ‒ Or rework them • Views integration ‒ Use the SqlWriterSubscriber data ‒ Two default views provided (SqlWS, WatchdogWS) ‒ Drop your own exported views into heisencache/views for automatic loading
  49. 51/58 | heisencache | © OSInet Frederic MARAND IMPLEMENTATION: UI

    • Data collecting: raw data, big volume • Three-step data processing ‒ Collect Heisencache → ‒ Cook Process data based on your needs → ‒ Consumer Visualize processed data → • Sweet spot ‒ Use a queue (Beanstalkd, etc) instead of cron ‒ Push to RRD for longitudinal analysis (Munin, etc)
  50. 52/58 | heisencache | © OSInet Frederic MARAND IMPLEMENTATION: UI

    Comparing with network analysis • Heisencache is like ‒ libpcap / tcpdump / iptrace / snoop ... • Someone has to design a Wireshark on top of it
  51. 53/58 | heisencache | © OSInet Frederic MARAND CONTEXT MEASURING

    IMPLEMENTATION RESULTS
  52. 54/58 | heisencache | © OSInet Frederic MARAND RESULTS: instant

    data TYPICAL USEFUL INSTANT RESULTS • Repeated misses – Usual suspects: default Memcached and big writes (prod) – Rewriting a variable on most pages (dev) • Many calls to same key – Usual suspect: missing or broken static cache • Many calls to related keys – Usual suspect: code loop instead of cache multiple
  53. 55/58 | heisencache | © OSInet Frederic MARAND RESULTS: longitudinal

    analysis TYPICAL USEFUL TIME-SERIES RESULTS • Size of known-to-be-growing keys. Usual suspects: – Translation cache Someone left a → t($foo) somewhere – Context cache Contexts are piled instead of refactored → – Views plugins Hard Views problem. Partial fix only. → • Miss rate shooting up from baseline on a bin – Call for instant analysis on that bin: likely a code regression • Response time shooting up on a normally stable key – Network/server problem, bin saturation – Call for instant analysis on the cache instance
  54. 56/58 | heisencache | © OSInet Frederic MARAND Drupal 8?

    SHOULD HAVE LESS CUSTOM CODE • Reuse Symfony components – Data visibiliy persisted via the Kernel – Ability to hook into boostrap – Configuration using services – Shutdown events
  55. 57/58 | heisencache | © OSInet Frederic MARAND Drupal 8?

    WHEN? • When bigger sites start to deploy D8 • …and need them to go faster :-)
  56. 58/58 | heisencache | © OSInet Frederic MARAND Drupal, faster

    http://www.osinet.fr/