Scala Use Cases at Hatena

by mechairoi

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Scala Use Cases at Hatena גࣜձࣾ͸ͯͳ Takaya Tsujikawa https://www.ﬂickr.com/photos/30081184@N02/3769383676

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Takaya Tsujikawa (@mechairoi) blog.chairoi.me mechairoi ! - 2009 Hatena Intern (Perl) - 2011 Joined Hatena (Perl) - 2013~ Mackerel team lead engineer (Scala)

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Table of Contents • Web development with Perl & problems • Why Scala? • Web development with Scala • Pros & Cons

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• Internet Company 2001~ • Hatena Bookmark • Hatena Blog • Flipnote Hatena etc. • Almost products by Perl

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Why Perl?

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– http://www.paulgraham.com/hp.html “We need a language that lets us scribble and smudge and smear, not a language where you have to sit with a teacup of types balanced on your knee and make polite conversation with a strict old aunt of a compiler”

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Why Perl? (200x) • CPAN • Rapid prototyping • Code density ⛳️ • Duck typing • Perl Community (YAPC etc)

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a decade later … https://www.ﬂickr.com/photos/josh/11029669/in/photolist-YwJH-dZrHB3-dZro3Y-dZkJSF-dZrn6b-dZkTkH-dZm2se-dZkN5R-dZrFnG-dZm1Lc-aEwYeQ-8cKHdX-aGrYEa-593eo9-eUa2aU- eZXyHe-f1cTP9-dZkQzP-dZrJps-dZkYtg-dZm3gp-dZkAwV-dZkyLc-dZrhAo-dZrjiC-dZrgmN-dZrifq-dZri1Y-dZkS2a-dZkVoM-eUar2C-dZrhLu-a3hhH4-dZruES-eTXXbc-dZkUhB-dZkCJF- dZrmTY-dZrCXS-dZkEYz-dZkZsz-dZkZJZ-dZrrTb-dZkGH2-dZrkZ5-dZrp1N-dZrpNG-dZrHYQ-dZrq5C-dZrsA1/

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Web applications become more complex https://www.ﬂickr.com/photos/adrian_s/8271860/in/photolist-JoWh-2J1ULn-5MBjL1-7Jb7po-PBm6n-4YxhWQ-ftWYrC-56q8A8-byH7Vo-g6K6Gv-aiH2Kq-oqCruv-wJ9B-6qtmTj- bzvmcN-8SLbUW-4EUk2k-7WsSCV-6WR5CX-bQkpxT-EN7qe-5i3Tcf-aUrm1H-8ZRy8r-aBUFd2-6jBeaS-8N6ZoM-ig1HkK-4Ut5PG-8t8Q6D-5KjrEv-4cTcqP-3feujT-7Bpbqh- atG3JH-22M7W-8cwtgh-5jQDxs-EN7nt-cc87U3-6Zmv7D-4q13tN-9MqM4o-dK4pWN-8agRiA-GK1af-crBgSU-7NVEST-9Lg7jB-6KRFX Business Library Update Legacy Code New features Mobile

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Resistance to collapse • Coding rule • Code review • Test / Continuous integration • Testing is require but not sufﬁcient • Static code analysis IUUQTXXXqJDLSDPNQIPUPT!/

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ʊਓਓਓਓਓਓਓਓਓਓਓਓਓʊ ʼɹSudden Runtime Errorɹʻ ʉY^Y^Y^Y^Y^Y^Y^Y^Y^Y^Y^Yʉ

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We need static typing https://www.ﬂickr.com/photos/hetgacom/10420400556/in/photostream/

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Why xxScala?

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New Project!

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A New Kind of Application Performance Management

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Push architecture host1 host2 host3 Mackerel Agent

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Graphs by roles cpu usage of proxies loadavg5 of apps

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Monitoring • Mail • Webhook

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Background • 2013/11 Start • 1 engineer + Outsource • B2B • Low dependency to existing system.(ex. Account system) • Owned service • Less restriction Chance of introduction of new technology

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Go Graphite PostgreSQL

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Go Graphite PostgreSQL

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Requirements • Modern type system • Lots of libraries • Case studies of web development • Member’s Skill

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Why Scala (1/4) • Modern type system • Static typing • Algebraic data type (case class, sealed trait) • Type inference • Ad hoc polymorphism (implicit conversion) • B2B Safe refactoring and improvement

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Why Scala (2/4) • Lots of libraries

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Why Scala (3/4) • Case studies of web development

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Why Scala (4/4) • Member’s skills • some members had been studied/was interested in Scala • Product must not depend on individual skills

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Other languages • Java8 • Not available yet • Haskell • Hard to assemble team • Go/Ruby • No modern type system

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Development with Scala

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• Fullstack WAF • Routing • Type-safe template engine • play.api.{data.Form, libs.Json} • Pretty error messages • play-auth/stackable-controller

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• Type safe template engine (Twirl) • Our designer writes Scala expression • Hard for designer • Rewriting Angularjs template • 2.2.1 → 2.2.2 → 2.3.1

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Design policy • MVC • Classes • object models.Users #create • Side effects • case class models.User (email: String, … ) • Immutable data container • No side effects, no variable.

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In Perl case ! Side effects are used everywhere

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Design policy • Less variable, less mutable collection, less partial function ( Option#get ) • User deﬁned types (Tagged Type) • UserId / HostId instead of Int • UserName instead of String Increase guarantee by type

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In Perl case ! No static typing Just try hard

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Design policy • Mapping primitive type and domain types by type classes )551CPEZ ! 63* ! %BUBTUPSF "QQMJDBUJPO .PEFM .BQQJOHCZ UZQFDMBTT 4USJOH +40/ KBWBMBOH42- DBTFDMBTTFT 6TFS )PTU

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Routing GET /hosts/:id controllers.Hosts.retrieve(id: HostId) implicit def hostIdFormat: Formatter[HostId] = new Formatter[HostId] { def bind(key: String, data: Map[String, String]) : Either[Seq[FormError], HostId] = ??? ! def unbind(key: String, value: HostId) = ??? } …

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Modules • Modularize for compile speed ( In progress..) $PSF5ZQFT $PSF .PEFMT $PSF$POUSPMMFST $PSF 7JFXT "MFSU5ZQFT "MFSU .PEFMT "MFSU$POUSPMMFST "MFSU 7JFXT 3PPU 3FWFSTF 3PVUFS

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• Schema code generation • Type-safe queries and raw queries • All Queries in our product are type-safe • Extends for “FOR UPDATE OF t1” • 1.0.1 → 2.0.0 → 2.0.3 ( → 2.1.0)

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Build complex queries easily and safely val statusById: Map[AlertId, MonitorStatus] = (for { (log, logLater) <- Tables.alertLogs(orgId) leftJoin Tables.alertLogs(orgId) on { case (log, logLater) => log.createdAt < logLater.createdAt && log.alertId === logLater.alertId } if log.alertId inSetBind entities.map(_.id) if logLater.createdAt.?.isNull } yield (log.alertId, log.status)).list.toMap

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Build complex queries easily and safely val statusById: Map[AlertId, MonitorStatus] = (for {! (log, logLater) <- Tables.alertLogs(orgId) leftJoin! Tables.alertLogs(orgId) on { case (log, logLater) =>! log.createdAt < logLater.createdAt &&! log.alertId === logLater.alertId! }! if log.alertId inSetBind entities.map(_.id)! if logLater.createdAt.?.isNull! } yield (log.alertId, log.status)).list.toMap

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Not human readable select x2.x3, x2.x4 from (select x5."updated_at" as x6, x5."status" as x4, x5."alert_id" as x3, x5."created_at" as x7, x5."operator_ id" as x8, x5."id" as x9, x5."trigger" as x10 from "alert_logs" x5, "alerts" x11 where (x11."id" = x5."alert_id") and (x11."org_id" = ?)) x2 left outer join (select x12."updated_at" as x13, x12."status" as x14, x12."alert_id" as x15, x12."created_at" as x16, x12."operator_id" as x17, x12."id" as x18, x12."trigger" as x19 from "alert_logs" x12, "alerts" x20 where (x20."id" = x12."alert_id") and (x20."org_id" = ?)) x21 on (x2.x7 < x21.x16) and (x2.x3 = x21.x15) where (x2.x3 in (?)) and (x21.x16 is null)

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Not human readable select x2.x3, x2.x4 from (select x5.x6 as x7, x5.x8 as x9, x5.x10 as x11, x5.x12 as x13, x5.x14 as x15, x5.x16 as x17, x5.x18 as x3, x5.x19 as x20, x5.x21 as x22, x5.x23 as x24, x5.x25 as x26, x5.x27 as x28, x5.x29 as x30, x5.x31 as x32, x5.x33 as x34, x5.x35 as x36, x37.x38 as x39, x37.x40 as x4, x37.x41 as x42, x37.x43 as x44, x37.x45 as x46, x37.x47 as x48, x37.x49 as x50, x37.x51 as x52 from (select x53."updated_at" as x6, x53."image_url" as x8, x53."hosts_count_limit" as x10, x53."webhook_url" as x12, x53."enabled_experimental_features" as x14, x53."created_at" as x16, x53."id" as x18, x53."owner_team_id" as x19, x53."name" as x21, x53."gravatar_email" as x23, x53."is_staff" as x25, x53."notification_activates_at" as x27, x53."plan_id" as x29, x53."plan_expired_at" as x31, x53."author_id" as x33, x53."token" as x35 from "orgs" x53) x5 left outer join (select x54."updated_at" as x38, x54."agv_count" as x40, x54."max_count" as x41, x54."total" as x43, x54."created_at" as x45, x54."base_datetime" as x47, x54."id" as x49, x54."org_id" as x51 from "host_metrics_counts" x54) x37 on x5.x18 = x37.x51) x2 left outer join (select x55."updated_at" as x56, x55."agv_count" as x57, x55."max_count" as x58, x55."total" as x59, x55."created_at" as x60, x55."base_datetime" as x61, x55."id" as x62, x55."org_id" as x63 from "host_metrics_counts" x55) x64 on (x2.x3 = x64.x63) and (x2.x48 < x64.x61) where ((x2.x3 in (?)) and (x64.x61 is null)) and (x2.x48 > {ts '2014-09-02 17:27:18.039'}) • Where does code generate this query?

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In Perl case • No type-safe • Publisher class in SQL Comment SELECT * FROM user WHERE user_id = ?; -- Hatena::User

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Development ﬂow

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IDE AND / OR

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Git Branches operation NBTUFS EFWFMPQ GFBUVSF GFBUVSF 3FMFBTF

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Git Branches operation NBTUFS EFWFMPQ GFBUVSF GFBUVSF 3FMFBTF No accident on merge

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In Perl case ＿人人人人人人人人人＿＞�Merge without conflicts�＜ ‾Y^Y^Y^Y^Y^Y^Y^Y‾ Can't locate object method "retrieve_by_id" via package "Entry" at error.pl line 21. Entry->retrieve_by_id(10); Entry->retrieve(id => 10); Entry->retrieve_by_id(20); 3FGBDUPSJOH "EEFEDBMMT

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Task management • Github issues/pull requests • Tag • Milestone

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Scrum • Sprint = Milestone • Burn down chart • radekstepan/github-burndown-chart

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Jenkins/CI • Test & Packaging parallel • 1h → 20min • Git integration

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git-pr-release • Auto generate pull-request • master ← develop • Check list / issues • Everyone can deploy • motemen/git-pr-release

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Deploy • Restarting JVM is slow → 502 • Capistrano • Custom deploy strategy • scp jar ﬁles from Jenkins • Rolling deploy • daemontools https://www.ﬂickr.com/photos/gsfc/9807812154/in/photolist-fWFARy-dBeVvk-96iJmd-atSZgv-hFZzw8-aoA2hH-j2aiC2-mrQV5-kwW6fT-9MP2Ju-edaJM7-M3WWJ-kmUfnB-dxxRza- Cjb4u-4YSS4-8JpmiE-4yjdpB-bbibXF-btu7MA-bGoWje-kTaXqi-jJpjHn-5RV54-4rMctW-bGoWnD-ecFBPp-9Yf9KD-9XsGPA-LVDt-aRcVjM-5xgexk-9S6d4F-4y4qNv-eZwRu-osQq9g-ebMkug- ed9XJo-qyM6W-aUyKZH-4cxiEU-bGoWsk-btu7F1-776kcJ-9zuC1x-j2bH1R-bypWd7-e6BdUN-bGoWeX-btu7A7

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In Perl case • Capistrano • git clone • Server::Starter • Graceful restart

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Scala Pros & Cons

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Pros https://www.ﬂickr.com/photos/quinndombrowski/5200218267/in/photolist-6k8go4-a3y271-8VwtHD-skiqN-nN34SF-bveV1T-cjNRK9-oddpGc-6SXagE-fea96C-6MLPeT-a7pJhj-wDorR- a55adA-8uYbhg-4HP2Qm-dhuorr-aYXd4F-eLGkd-e4eFKc-9ugzpc-6MZ9UU-bWXfCV-9GH9mD-59UEA7-aG95zM-3fJmjC-cHPX65-8aBfdr-j7GYKE-e6ViAm-bAhx1p-feQRPa-92JZzp-kLtFHa- XWd9L-9zbeGs-9DdEqR-8maR73-nBgwNS-8WFsTq-7wSNi8-MvvjP-5DMyrq-8Kowmj-54rxHi-BqUvC-fLbCYs-7F9di2-nR8Kt4

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Pros • Peace of Mind • Refactoring/Upgrade is easy • Can focus to architecture/design and logic in review • Functional programming • Collection libraries

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Cons • Slow compilation • modularize • high spec machine

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Cons • Require Java/JVM literacy • Rich language functions • Hard to learn • De-facto standard Job queue? • Mocking is difﬁcult in tests