Scio - A Scala API for Google Cloud Dataflow & Apache Beam

Scio
A Scala API for
Google Cloud Dataflow &
Apache Beam
Neville Li
@sinisa_lyh

About Us
● 100M+ active users, 40M+ paying
● 30M+ songs, 20K new per day
● 2B+ playlists
● 60+ markets
● 2500+ node Hadoop cluster
● 50TB logs per day
● 10K+ jobs per day

Who am I?
● Spotify NYC since 2011
● Formerly Yahoo! Search
● Music recommendations
● Data infrastructure
● Scala since 2013

Origin Story
● Python Luigi, circa 2011
● Scalding, Spark and Storm, circa 2013
● ML, recommendation, analytics
● 100+ Scala users, 500+ unique jobs

Moving to
Google
CloudEarly 2015 - Dataflow Scala hack project

The Evolution of Apache Beam
MapReduce
BigTable DremelColossus
FlumeMegastoreSpanner
PubSub
Millwheel
Apache
Beam
Google Cloud
Dataflow

What is Apache Beam?
1. The Beam Programming Model
2. SDKs for writing Beam pipelines -- starting with Java
3. Runners for existing distributed processing backends
○ Apache Flink (thanks to data Artisans)
○ Apache Spark (thanks to Cloudera and PayPal)
○ Google Cloud Dataflow (fully managed service)
○ Local runner for testing

9
The Beam Model: Asking the Right Questions
What results are calculated?
Where in event time are results calculated?
When in processing time are results materialized?
How do refinements of results relate?

10
Customizing What Where When How
3
Streaming
4
Streaming
+ Accumulation
1
Classic
Batch
2
Windowed
Batch

11
The Apache Beam Vision
1. End users: who want to write
pipelines in a language that’s familiar.
2. SDK writers: who want to make Beam
concepts available in new languages.
3. Runner writers: who have a
distributed processing environment
and want to support Beam pipelines
Beam Model: Fn Runners
Apache
Flink
Apache
Spark
Beam Model: Pipeline Construction
Other
LanguagesBeam Java
Beam
Python
Execution Execution
Cloud
Dataflow
Execution

Data model
Spark
● RDD for batch, DStream for streaming
● Two sets of APIs
● Explicit caching semantics
Dataflow / Beam
● PCollection for batch and streaming
● One unified API
● Windowed and timestamped values

Execution
Spark
● One driver, n executors
● Dynamic execution from driver
● Transforms and actions
Dataflow / Beam
● No master
● Static execution planning
● Transforms only, no actions

Scalding on Google Cloud
Pros
● Community - Twitter, Stripe, Etsy, eBay
● Hadoop stable and proven
Cons
● Cluster ops
● Multi-tenancy - resource contention and utilization
● No streaming (Summingbird?)
● Integration with GCP - BigQuery, Bigtable, Datastore, Pubsub

Spark on Google Cloud
Pros
● Batch, streaming, interactive, SQL and MLLib
● Scala, Java, Python and R
● Zeppelin, spark-notebook
Cons
● Cluster lifecycle management
● Hard to tune and scale
● Integration with GCP - BigQuery, Bigtable, Datastore, Pubsub

Dataflow
● Hosted, fully managed, no ops
● GCP ecosystem - BigQuery, Bigtable, Datastore, Pubsub
● Unified batch and streaming model
Scala
● High level DSL
● Functional programming natural fit for data
● Numerical libraries - Breeze, Algebird
Why Dataflow with Scala

Cloud
Storage
Pub/Sub Datastore BigtableBigQuery
Batch Streaming Interactive REPL
Scio Scala API
Dataflow Java SDK Scala Libraries
Extra features

Scio
Ecclesiastical Latin IPA: /ˈʃi.o/, [ˈʃiː.o], [ˈʃi.i̯o]
Verb: I can, know, understand, have knowledge.

github.com/spotify/scio
Apache Licence 2.0

WordCount
val sc = ScioContext()
sc.textFile("shakespeare.txt")
.flatMap { _
.split("[^a-zA-Z']+")
.filter(_.nonEmpty)
}
.countByValue
.saveAsTextFile("wordcount.txt")
sc.close()

PageRank
def pageRank(in: SCollection[(String, String)]) = {
val links = in.groupByKey()
var ranks = links.mapValues(_ => 1.0)
for (i <- 1 to 10) {
val contribs = links.join(ranks).values
.flatMap { case (urls, rank) =>
val size = urls.size
urls.map((_, rank / size))
}
ranks = contribs.sumByKey.mapValues((1 - 0.85) + 0.85 * _)
}
ranks
}

Type safe BigQuery
Macro generated case classes, schemas and converters
@BigQuery.fromQuery("SELECT id, name FROM [users] WHERE ...")
class User // look mom no code!
sc.typedBigQuery[User]().map(u => (u.id, u.name))
@BigQuery.toTable
case class Score(id: String, score: Double)
data.map(kv => Score(kv._1, kv._2)).saveAsTypedBigQuery("table")

REPL
$ scio-repl
Welcome to
_____
________________(_)_____
__ ___/ ___/_ /_ __
_(__ )/ /__ _ / / /_/ /
/____/ ___/ /_/ ____/ version 0.2.5
Using Scala version 2.11.8 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_11)
Type in expressions to have them evaluated.
Type :help for more information.
Using 'scio-test' as your BigQuery project.
BigQuery client available as 'bq'
Scio context available as 'sc'
scio> _
Available in github.com/spotify/homebrew-public

Future based orchestration
// Job 1
val f: Future[Tap[String]] = data1.saveAsTextFile("output")
sc1.close() // submit job
val t: Tap[String] = Await.result(f)
t.value.foreach(println) // Iterator[String]
// Job 2
val sc2 = ScioContext(options)
val data2: SCollection[String] = t.open(sc2)

DistCache
val sw = sc.distCache("gs://bucket/stopwords.txt") { f =>
Source.fromFile(f).getLines().toSet
}
sc.textFile("gs://bucket/shakespeare.txt")
.flatMap { _
.split("[^a-zA-Z']+")
.filter(w => w.nonEmpty && !sw().contains(w))
}
.countByValue
.saveAsTextFile("wordcount.txt")

● DAG visualization & source code mapping
● BigQuery caching, legacy & SQL 2011 support
● HDFS Source/Sink, Protobuf & object file I/O
● Job metrics, e.g. accumulators
○ Programmatic access
○ Persist to file
● Bigtable
○ Multi-table write
○ Cluster scaling for bulk I/O
Other goodies

Adoption
● At Spotify
○ 20+ teams, 80+ users, 70+ production pipelines
○ Most of them new to Scala and Scio
● Open source model
○ Discussion on Slack, mailing list
○ Issue tracking on public Github
○ Community driven - type safe BigQuery, Bigtable, Datastore, Protobuf

Release Radar
● 50 n1-standard-1 workers
● 1 core 3.75GB RAM
● 130GB in - Avro & Bigtable
● 130GB out x 2 - Bigtable in US+EU
● 110M Bigtable mutations
● 120 LOC

Master Metadata
● n1-standard-1 workers
● 1 core 3.75GB RAM
● Autoscaling 2-35 workers
● 26 Avro sources - artist, album, track, disc, cover art, ...
● 120GB out, 70M records
● 200 LOC vs original Java 600 LOC

BigDiffy
● Pairwise field-level statistical diff
● Diff 2 SCollection[T] given keyFn: T => String
● T: Avro, BigQuery, Protobuf
● Field level Δ - numeric, string, vector
● Δ statistics - min, max, μ, σ, etc.
● Non-deterministic fields
○ ignore field
○ treat "repeated" field as unordered list
Part of github.com/spotify/ratatool

Dataset Diff
● Diff stats
○ Global: # of SAME, DIFF, MISSING LHS/RHS
○ Key: key → SAME, DIFF, MISSING LHS/RHS
○ Field: field → min, max, μ, σ, etc.
● Use cases
○ Validating pipeline migration
○ Sanity checking ML models

Pairwise field-level deltas
val lKeyed = lhs.keyBy(keyFn)
val rKeyed = rhs.keyBy(keyFn)
val deltas = (lKeyed outerJoin rKeyed).map { case (k, (lOpt, rOpt)) =>
(lOpt, rOpt) match {
case (Some(l), Some(r)) =>
val ds = diffy(l, r) // Seq[Delta]
val dt = if (ds.isEmpty) SAME else DIFFERENT
(k, (ds, dt))
case (_, _) =>
val dt = if (lOpt.isDefined) MISSING_RHS else MISSING_LHS
(k, (Nil, dt))
}
}

Summing deltas
import com.twitter.algebird._
// convert deltas to map of (field → summable stats)
def deltasToMap(ds: Seq[Delta], dt: DeltaType)
: Map[String, (Long, Option[(DeltaType, Min[Double], Max[Double], Moments)])] = {
// ...
}
deltas
.map { case (_, (ds, dt)) => deltasToMap(ds, dt) }
.sum // Semigroup!

Other uses
● AB testing
○ Statistical analysis with bootstrap
and DimSum
○ BigQuery, Datastore, TBs in/out
● Monetization
○ Ads targeting
○ User conversion analysis
○ BigQuery, TBs in/out
● User understanding
○ Diversity
○ Session analysis
○ Behavior analysis
● Home page ranking
● Audio fingerprint analysis

Serialization
● Data ser/de
○ Scalding, Spark and Storm uses Kryo and Chill
○ Dataflow/Beam requires explicit Coder[T]
Sometimes inferable via Guava TypeToken
○ ClassTag to the rescue, fallback to Kryo/Chill
● Lambda ser/de
○ ClosureCleaner
○ Serializable and @transient lazy val

REPL
● Spark REPL transports lambda bytecode via HTTP
● Dataflow requires job jar for execution (no master)
● Custom class loader and ILoop
● Interpreted classes → job jar → job submission
● SCollection[T]#closeAndCollect(): Iterator[T]
to mimic Spark actions

Macros and IntelliJ IDEA
● IntelliJ IDEA does not see macro expanded classes
https://youtrack.jetbrains.com/issue/SCL-8834
● @BigQueryType.{fromTable, fromQuery}
class MyRecord
● Scio IDEA plugin
https://github.com/spotify/scio-idea-plugin

Scio in Apache Zeppelin
Local Zeppelin server, remote managed Dataflow cluster, NO OPS

Experimental
● github.com/nevillelyh/shapeless-datatype
○ Case class ↔ BigQuery TableRow & Datastore Entity
○ Generic mapper between case class types
○ Type and lens based record matcher
● github.com/nevillelyh/protobuf-generic
○ Generic Protobuf manipulation similar to Avro GenericRecord
○ Protobuf type T → JSON schema
○ Bytes ↔ JSON given JSON schema

What's Next?
● Better streaming support [#163]
● Support Beam 0.3.0-incubating
● Support other runners
● Donate to Beam as Scala DSL [BEAM-302]

The End
Thank You
Neville Li
@sinisa_lyh

Scio - A Scala API for Google Cloud Dataflow & Apache Beam

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