Patella railsconf 2012

PATELLAMEMOIZATION INTO MEMCACHED DONE IN RESQUEJEFF DWYERPATIENTSLIKEME@JDWYAH

TODAYEngineers will never be successful if we are the brake oninnovation.Technique for innovating safelyLearn a bit about meta-programming

TODAYSetup the problemSketch the solutionNitty Gritty Details

1) NIH PRESENTATIONIN 4 WEEKS!Integrate clinicaltrials.gov into our siteSearch by trial typeSearch by trial phaseSearch by trial conditions mapped from Mesh to MeddraSearch by trial facility locations… • Location search…

WE HAVE A CHOICE

WHAT IS RIGHTPostGIS spatial database extensions for PostgreSQLMongoDB built in support for two dimensional geospatial indexes

AND WHAT IS EASYsqrt(pow(69.1 * (clinical_trial_locations.lat - 40.948073),2) + pow(53.0 * (clinical_trial_locations.lng - -90.36871),2)) AS distance

CHOOSE THE EASY!

CHOOSE THE EASY!Who knows if location is even important?Who knows if this project is even important?MongoDB requires dev setup, automated stagingsetup, production setup, monitoring.

BUT, OH GOD THEHUMANITY<query plan pic>

2) PATIENT LIKE ME SEARCH

PATIENT SEARCH RANKINGVery basic searchPlus very complex orderingNot as many great solutions in this spaceN^2 similarity matrix @ 100k patients about 4 TBAnd did I mention it’s N^2?Postgres is an amazingly viable solution.

ELEGANT CODE…

LOVELY SQL…

BUT IT’S JUST THISSIDE OF ‘REAL-TIME’One second queries just don’t fly.And oh, yeah 16 people hitting it at the same time wouldclobber the servers.

3) A FORWARD LOOKINGTIME MACHINEMaybe those were aberrations?Crazy right?

A FORWARD LOOKINGTIME MACHINE

AND HERE’S MY CEO PROMISING ITAT TED

A FORWARD LOOKINGTIME MACHINE

STEPPING BACKConflict • Relational data is most easily queried relationally. • Relational queries don’t necessarily scale and stay in the millisecond range • Denormalized queries & special solutions scale • But take longer to implement • (note) This isn’t just SQL, I’m talking about anything slowWe want to experiment/fail fast • But we don’t want…

DON’T WANT TO LET THIS:

TURN INTO:

TURN INTO: :-C

WHAT WE WANTTrivially easy way for developers to declare that somemethods are not to be run without adult supervision.Consistent framework so that ops doesn’t need to be afraidof new, sometimes expensive experiments.

SOLUTION SPACEDoing it right all the time • Too slow and expensive • Slows innovation

SOLUTION SPACEMemoization • Brilliant • Functional Programming Nirvana • No cache-key shenanagins • But also no expiry… • There’s just one thing… • It only works in a single request

SOLUTION SPACEMemcached • Great • Simple to setup. • Could be simpler. Handmade cache keys feels wrong. • But it doesn’t solve our :-C problem. • The first request still slams the server. • So you do some cache warming thing… • But this is a PITA again.

WHAT COULD MAKETHIS SIMPLER?Remove one constraint.A basic Rails.cache.fetch guarantees you a result • But no performance guaranteeFlip that deal around. • Guarantee performance • Don’t guarantee a result • It’s ok not to know the answer!

BUT IT NEEDS A NAME!

TECHNOLOGIES!Memoization into Memcached with everything calculated inResque.

PATELLA DEVELOPERINTERFACE

SEND LATERSuper easy way to just do something later while in the samecontext.Most workers are real boring.Single worker for suffices for many background jobs.Makes testing/development easier by bypassing Resque inconfiguration.AR extension. Coordinates logging / monitoring.

SENDLATER User.send_later :expensive, arg1, arag2

SENDLATER RESQUEWORKER

MEMOIZATIONSendLater gets things calculated in Resque, but that’s step 1.We still need:Memoization.Stored in memcached.

THIS IS NOT A GOOD SLIDE

PATELLA RESULT

THE METHOD

WITH PATELLA

THE REPLACEMENT

THE ONE THAT DOESTHE WORK

MAYBE IT’S BETTER NOW?

DOG PILE

THE REPLACEMENT

DOG PILE

LONG ARGUMENTS

SOFT EXPIRATIONMemcached is great, but it doesn’t tell you when somethingexpires.Our strategy was to add a ‘soft_expiry’This gets stored along with the result.Then recalculate if soft_expiry < now()

ABJALWAYS BE JSONBeware putting not JSON in memcachedYou really don’t want to know

META IS MAGIC

REAL LIFE

PRETTY BORINGExcept that it works. Round 1: Major Pain Points Round 2: Magic Scaling SprinklesSuper alpha gem here: https://github.com/kbrock/patellaAlternative https://github.com/csquared/rack-worker Very REST-ish, request based.

JOE@JOERODRIGUEZ

AMY@AMYNEWELL

KEENAN@KBROCK

WINFIELD@WPETERSON

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Patella railsconf 2012

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