#CASSANDRA13 CASSANDRASUMMIT2013 Cassandra adoption at Hailo from three perspectives: 1. Development 2. Operational 3. Management What this talk is about
#CASSANDRA13 CASSANDRASUMMIT2013 • The world’s highest-rated taxi app – over 10,000 five-star reviews • Over 500,000 registered passengers • A Hailo e-hail is accepted by a driver every four seconds around the world • Hailo operates in ten cities from Tokyo to Toronto in just over eighteen months of operation What is Hailo?
#CASSANDRA13 CASSANDRASUMMIT2013 • Hailo is a marketplace that facilitates over $100M in run-rate transactions and is making the world a better place for passengers and drivers • Hailo has raised over $50M in financing from the world's best investors including Union Square Ventures, Accel, the founder of Skype (via Atomico), Wellington Partners (Spotify), Sir Richard Branson, and our CEO's mother, Janice Hailo is growing
#CASSANDRA13 CASSANDRASUMMIT2013 Hailo launched in London in November 2011 • Launched on AWS • Two PHP/MySQL web apps plus a Java backend • Mostly built by a team of 3 or 4 backend engineers • MySQL multi-master for single AZ resilience
#CASSANDRA13 CASSANDRASUMMIT2013 Why Cassandra? • A desire for greater resilience – “become a utility” Cassandra is designed for high availability • Plans for international expansion around a single consumer app Cassandra is good at global replication • Expected growth Cassandra scales linearly for both reads and writes • Prior experience I had experience with Cassandra and could recommend it
#CASSANDRA13 CASSANDRASUMMIT2013 The path to adoption • Largely unilateral decision by developers – a result of a startup culture • Replacement of key consumer app functionality, splitting up the PHP/MySQL web app into a mixture of global PHP/Java services backed by a Cassandra data store • Launched into production in September 2012 – originally just powering North American expansion, before gradually switching over Dublin and London
#CASSANDRA13 CASSANDRASUMMIT2013 Considerations for entity storage • Do not read the entire entity, update one property and then write back a mutation containing every column • Only mutate columns that have been set • This avoids read-before-write race conditions
#CASSANDRA13 CASSANDRASUMMIT2013 Considerations for time series storage • Choose row key carefully, since this partitions the records • Think about how many records you want in a single row • Denormalise on write into many indexes
#CASSANDRA13 CASSANDRASUMMIT2013 Analytics • With Cassandra we lost the ability to carry out analytics eg: COUNT, SUM, AVG, GROUP BY • We use Acunu Analytics to give us this abilty in real time, for pre- planned query templates • It is backed by Cassandra and therefore highly available, resilient and globally distributed • Integration is straightforward
#CASSANDRA13 CASSANDRASUMMIT2013 AQL SELECT SUM(accepted), SUM(ignored), SUM(declined), SUM(withdrawn) FROM Allocations WHERE timestamp BETWEEN '1 week ago' AND 'now’ AND driver='LON123456789’ GROUP BY timestamp(day)
#CASSANDRA13 CASSANDRASUMMIT2013 Learn the theory • Teach each team member the fundamentals • CQL can encourage an SQL mindset, but it’s important to understand the underlying data model • Make a real effort to share knowledge – keep in mind the gulf in experience for most team members between their old world and the new world (SQL vs NoSQL) • Peer review data models
#CASSANDRA13 CASSANDRASUMMIT2013 “Allows a team of 2 to achieve things they wouldn’t have considered before Cassandra existed” Chris H, Operations Engineer
#CASSANDRA13 CASSANDRASUMMIT2013 Backups • SSTable snapshot • Used to upload to S3, but this was taking >6 hours and consuming all our network bandwidth • Now take EBS snapshot of the SSTable snapshots
#CASSANDRA13 CASSANDRASUMMIT2013 Encryption • Requirement for NYC launch • We use dmcrypt to encrypt the entire EBS volume • Chose dmcrypt because it is uncomplicated • Our tests show a 1% performance hit in disk performance, which concurs with what Amazon suggest
#CASSANDRA13 CASSANDRASUMMIT2013 Datastax Ops Centre • We run the free version • Offers up easily accessible “one screen” overviews of the activity of the entire cluster • Big fans – an easy win
#CASSANDRA13 CASSANDRASUMMIT2013 Multi DC • Something that Cassandra makes trivial • Would have been very difficult to accomplish active-active inter-DC replication with a team of 2 without Cassandra • Rolling repair needed to make it safe (we use LOCAL_QUORUM) • We schedule “narrow repairs” on different nodes in our cluster each night
#CASSANDRA13 CASSANDRASUMMIT2013 Compression • Our stats cluster was running at ~1.5TB per node • We didn’t want to add more nodes • With compression, we are now back to ~600GB • Easy to accomplish • `nodetool upgradesstables` on a rolling schedule
#CASSANDRA13 CASSANDRASUMMIT2013 Technically, everything is fine… • Our COO feels that C* is “technically good and beautiful”, a “perfectly good option” • Our EVPO says that C* reminds him of a time series database in use at Goldman Sachs that had “very good performance” …but there are concerns
#CASSANDRA13 CASSANDRASUMMIT2013 Keep the business informed • Pre-launch, we were tasked with increasing resiliency • Cassandra addressed immediate business needs, but the trade offs involved should have been communicated more clearly
#CASSANDRA13 CASSANDRASUMMIT2013 Sing from the same hymn sheet • A senior founding engineer had doubts about the adoption of Cassandra until very recently • In the presence of business doubt, this lack of consistency amongst developers exacerbated the concerns • We should have made more effort to make bilateral decisions on adoption – I don’t think this would have been hard to achieve
#CASSANDRA13 CASSANDRASUMMIT2013 Provide solutions • There are many options for ad-hoc querying of Cassandra • We underestimated the impact of not having a good solution for this from the very beginning
#CASSANDRA13 CASSANDRASUMMIT2013 Lessons for successful adoption • Have an advocate, sell the dream • Learn the fundamentals, get the best out of Cassandra • Invest in tools to make life easier • Keep management in the loop, explain the trade offs
#CASSANDRA13 CASSANDRASUMMIT2013 The future • We will continue to invest in Cassandra as we expand globally • We will hire people with experience running Cassandra • We will focus on expanding our reporting facilities • We aspire to extend our network (1M consumer installs, wallet) beyond cabs • We will continue to hire the best engineers in London, NYC and Asia
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