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Cabs, Cassandra and Hailo

Cabs, Cassandra and Hailo

The story of Cassandra use and adoption at Hailo, from development, operational and management perspective.

Dave Gardner

June 12, 2013
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  1. #CASSANDRA13
    Cassandra at Hailo
    David Gardner | Architect @ Hailo
    CASSANDRASUMMIT2013

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  2. #CASSANDRA13 CASSANDRASUMMIT2013

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    What is this talk about?

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    •  1,352 changed files with 235,413 additions and 47,487 deletions
    •  7,429 commits
    •  1,653 tickets completed
    https://github.com/apache/cassandra/compare/cassandra-0.6.0...cassandra-1.2
    https://github.com/apache/cassandra/blob/trunk/CHANGES.txt
    0.6 to 1.2

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  7. #CASSANDRA13 CASSANDRASUMMIT2013
    Cassandra adoption at Hailo from three perspectives:
    1.  Development
    2.  Operational
    3.  Management
    What this talk is about

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    What is Hailo?
    Hailo is The Taxi Magnet. Use Hailo to get a cab wherever you are, whenever you want.

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    •  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?

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    •  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

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  12. #CASSANDRA13 CASSANDRASUMMIT2013
    The history
    The story behind Cassandra adoption at Hailo

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  13. #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

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    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

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    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

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    Development perspective

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    “Cassandra just works”
    Dom W, Senior Engineer

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    Use cases
    1.  Entity storage
    2.  Time series data

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  19. #CASSANDRA13 CASSANDRASUMMIT2013
    CF = customers
    126007613634425612:
    createdTimestamp: 1370465412
    email: [email protected]
    givenName: Dave
    familyName: Gardner
    locale: en_GB
    phone: +447911111111

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    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

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    CF = comms
    2013-06-01:
    55374fa0-ce2b-11e2-8b8b-0800200c9a66: {“to”:”dave@c…
    a48bd800-ce2b-11e2-8b8b-0800200c9a66: {“to”:”foo@ex…
    b0e15850-ce2b-11e2-8b8b-0800200c9a66: {“to”:”bar@ho …
    bfac6c80-ce2b-11e2-8b8b-0800200c9a66: {“to”:”baz@fo…

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    CF = comms
    [email protected]:
    13b247f0-ce2c-11e2-8b8b-0800200c9a66: {“to”:”dave@c…
    20f70a40-ce2c-11e2-8b8b-0800200c9a66: {“to”:”dave@c…
    2b44d3b0-ce2c-11e2-8b8b-0800200c9a66: {“to”:”dave@c…
    338a22f0-ce2c-11e2-8b8b-0800200c9a66: {“to”:”dave@c…

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    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

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    Client libraries
    •  Astyanax (Java)
    •  phpcassa (PHP)
    •  github.com/carloscm/gossie (Go)

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    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

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    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)

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    Challenges

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    10 Average years experience
    per team member
    MySQL Cassandra

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    Lessons learned

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    Have an advocate
    •  Get someone who will sell the vision internally
    •  Make an effort to get everyone on board

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    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

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    Operational perspective

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    “Allows a team of 2 to achieve things they wouldn’t
    have considered before Cassandra existed”
    Chris H, Operations Engineer

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    2 clusters
    6 machines per region
    3 regions
    (stats cluster pending addition
    of third DC)
    Operational
    Cluster
    Stats
    Cluster
    ap-southeast-1 us-east-1 eu-west-1
    us-east-1 eu-west-1

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    AWS VPCs with Open
    VPN links
    3 AZs per region
    m1.large machines
    Provisoned IOPS EBS
    Operational
    Cluster
    Stats
    Cluster
    ~ 600GB/node
    ~ 100GB/node

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    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

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    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

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    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

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    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

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  48. #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

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    Lessons learned

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    Management perspective

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  52. #CASSANDRA13 CASSANDRASUMMIT2013
    “The days of the quick and dirty are over”
    Simon V, EVP Operations

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    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

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    People who can
    attempt to query
    MySQL
    People who can
    attempt to
    query Cassandra

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    Lessons learned

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    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

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    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

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  59. #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

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  60. #CASSANDRA13 CASSANDRASUMMIT2013
    People who can
    attempt to query
    MySQL
    People who can
    attempt to
    query Cassandra

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    Conclusions

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    We like Cassandra
    •  Solid design
    •  HA characteristics
    •  Easy multi-DC setup
    •  Simplicity of operation

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    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

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    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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  65. #CASSANDRA13
    Thank you
    CASSANDRASUMMIT2013

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