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Ähnlich wie Slash n: Tech Talk Track 2 – Website Architecture-Mistakes & Learnings - Siddhartha Reddy
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Slash n: Tech Talk Track 2 – Website Architecture-Mistakes & Learnings - Siddhartha Reddy
- 1. Flipkart Website Architecture Mistakes & Learnings Siddhartha Reddy Architect, Flipkart
- 2. June 2007
- 5. www.flipkart.com • Started in 2007 • Current Architecture from mid 2010 • Evolution of the architecture presented as… Issue[1] RCA[2] Actions Learnings • *1+ Issue: Website is “slow” • [2] RCA = Root Cause Analysis
- 6. Surviving & reacting to the environment INFANCY (2007 – MID-2010)
- 8. RCA • Why? – MySQL queries taking too long • Why? – Too many queries – Many slow queries – Queries locking tables • Why? – Capacity • Hmm…
- 9. Fixing it • Get beefier servers (the obvious) • Separate master_db, slave_db – Writes go to master_db – Reads from slave_db – Critical reads from master_db Writes Reads Reads Writes MySQL MySQL MySQL Replication Slave Master
- 10. Learning from it • Scale-out databases reads by distributing load across systems • Isolate database writes from reads – Writes are (usually) more critical
- 11. Website is “slow”! (Again)
- 12. RCA • Why? – MySQL queries taking too long (on slave_db) • Why? – Too many queries – Many slow queries • Why? – Queries from analytics / reporting and other backend jobs • Urm…
- 13. Fixing it • Analytics / reporting DB (archival_db) – Use MyISAM — optimized for reads – Additional indexes for quicker reporting Website Website Writes Reads Website Website Writes Reads MySQL MySQL Replication Slave 1 Master MySQL MySQL Replication Slave Master Replication Analytics MySQL Analytics Reads Slave 2 Reads
- 14. Learning from it • Isolate the databases being used for serving website traffic from those being used for analytical/reporting • Isolate systems being used by production website from those being used for background processing
- 15. Learning the basics BABY (2010 – 2011)
- 17. RCA • Why? • How? – Instrumentation
- 18. RCA - 1 • Why? – Logging a lot – PHP processes blocking on writing logs Request2 -> Process2 Writing Waiting Waiting Request1 Request3 Request2 Request2 Request3 -> Process1 -> Process3 :Process1 :Process2 :Process3 Log file
- 19. RCA - 2 • Why? – Service Oriented Architecture (SOA) – Too many calls to remote services per request • Creating fresh connection for each call • All the calls are made in serial order Connect to Request Connect Request Send Receive request Service1 Service1 Service2 Service2 response
- 20. RCA - 3 • Why? – Configurability – Fetch a lot of “config” from database for serving each request Receive Fetch Fetch Fetch Fetch Send request Config1 Config2 Config3 Config4 response
- 21. RCA – 1,2,3 • Why? – Logging a lot – SOA – Configurability • Why? – PHP’s process model • Argh!
- 22. Fixing it • fk-w3-agent – Simple Java “middleware” daemon – Deployed on each web server – PHP communicates to it through local socket – Hosts pluggable “handlers”
- 23. fk-w3-agent: LoggingHandler Request2 Request2 -> Process2 -> Process2 Request1 Request3 Request1 Request3 -> Process1 -> Process3 -> Process1 -> Process3 fk-w3- Log file agent Async / buffered Log file
- 24. fk-w3-agent: ServiceHandler(s) Connect to Request Connect Request Send Receive request Service1 Service1 Service2 Service2 response Call Receive request Send response fk-w3-agent fk-w3- agent Service1 Service2
- 25. fk-w3-agent: ConfigHandler Receive Fetch Fetch Fetch Fetch Send request Config1 Config2 Config3 Config4 response Database Fetch all config from Receive request Send response fk-w3-agent fk-w3- agent Poll and cache Database
- 26. Learning from it • PHP — good for frontend and templating – Gives a lot of agility – Limiting process model • Hurdle for high performance • Java — stability and performance • Horses for courses
- 27. Website is “slow”! (Again)
- 28. RCA • Why? – PHP processes taking up too much time – PHP processes taking up too much CPU • Why? – Product info deserialization taking up time/CPU – View construction taking up time/CPU
- 29. Fixing it • Caching! • Cache fully constructed pages – For a few minutes – Only for highly trafficked pages (Homepage) • Cache PHP serialized Product objects – ~20 million objects – Memcache • Yeah! But… – Add caching => add complexity
- 30. Caching: Complications (1) • “Caching fully constructed pages” • But parts of pages still need to be dynamic • Example: Logged-in user’s name • Impossible to do effective bucket testing • Or at least makes it prohibitively complex
- 31. Caching: Complications (2) • “Caching PHP serialized Product objects” • Without caching: getProductInfo() Fetch from CMS • With caching, cache hit: getProductInfo() Fetch from Cache • With caching, cache miss: Fetch from Fetch from getProductInfo() Set in Cache Cache CMS
- 32. Caching: Complications (3) • TTL: ∞ (i.e. no invalidation) • Pro-actively repopulate products in the cache – Receive “notifications” about product updates • Notification Server — pushes notifications raised by CMS • Use a persistent, distributed cache – Memcache => Membase, Couchbase
- 33. Learning from it • Caching is a powerful tool for performance optimization • Caching adds complexities – Reduced by keeping cache close to data source – Think deeply about TTL, invalidation • Use caching to go from “acceptable performance” to “awesome performance” – Don’t rely on it to get to “acceptable performance”
- 36. RCA • Why? – Search-service is slow (or Reviews-service is slow or Recommendations-service is slow) • But why is rest of website slow? – Requests to the slow service are blocking processing threads • Eh?!
- 37. Let’s do some math • Let’s say – Mean (or median) response time: 100 ms – 8-core server – All requests are CPU bound • Throughput: 80 requests per second (rps) • Let’s also say – 95th Percentile response time: 1000 ms • Call them “bad requests” • 4 bad requests in a second – Throughput down to 44 rps • 8 bad requests in a second? – Throughput down to 8 rps
- 38. Fixing it • Aggressive timeouts for all service calls – Isolate impact of a slow service • only to pages that depend on it • Very aggressive timeouts for non-critical services – Example: Recommendations • On a Product page, Search results page etc. • Not on My Recommendations page • Load non-critical parts of pages through AJAX
- 39. Learning from it • Isolate the impact of a poorly performing services / systems • Isolate the required from the good-to-have
- 40. Website is “slow”! (Again)
- 41. RCA • Why? – Load average of web servers has spiked • Why? – Requests per second has spiked • From 1000 rps to 1500 rps • Why? – Large number of notifications of product information updates
- 42. Fixing it • Separate cluster for receiving product info update notifications from the cluster that serves users • Admission control: Don’t let a system receive more requests than it can handle – Throttling • Batch the notifications
- 43. Learning from it • Isolate the systems serving internal requests from those serving production traffic • Admission control to ensure that a system is isolated from the over-enthusiasm of a client • Look at the granularity at which we’re working
- 46. THANK YOU
- 47. Mistake? • Sub-optimal decision – Not all information/scenarios considered – Insufficient information – Built for a different scenario • Due to focus on “functional” aspects • A mistake is a mistake – … in retrospect
Hinweis der Redaktion
- “This has basically given us lots of opportunities to make mistakes. And make mistakes we did.”
- Website Architecture diagram goes here
- No