mercari.go #11 @nsega Introduction to singleflight

About Me ● Naoki Sega (Twitter/GitHub: @nsega ) ● Backend Team in Mercari JP / Category Growth, Catalogs ● Joined Mercari JP in November 2018. ● Go : Experienced about 1 year in coding as the Production Code. ● Community : Kubernetes Meetup, Cloud Native Meetup, etc ● My current interests: Go, GCP, Kubernetes, Microservices,etc.

Agenda

Agenda ● What is singleflight? ● Introduction to use case 1 ● Introduction to use case 2 ● Conclusion

What is singleflight?

What is singleflight? ● “Package singleflight provides a duplicate function call suppression mechanism.” ● If your app receive multiple requests for the same resource, sync/singleflight is helpful. ○ RDB( master data ) ○ Image file ○ Lookup IP address ○ Client Certs ● “x/sync/singleflight” is imported by 81 packages (As of Oct 7 2019). ○ github.com/hashicorp/consul/agent/consul ○ gopkg.in/ebay/fabio.v1/cert ■ https://github.com/fabiolb/fabio/blob/master/cert/source.go https://godoc.org/golang.org/x/sync/singleflight?importers

What is singleflight? ● “Package singleflight provides a duplicate function call suppression mechanism.” ● ● ● ● ● https://godoc.org/golang.org/x/sync/singleflight

● Originally, singleflight had been using as standard library. (e.g. “net/lookup.go”) The spec is a little bit different between internal/singleflight and x/sync/singleflight. ● GoDoc - x/sync/singleflight, GoDoc - internal/singleflight Go Sync ( This repository provides Go concurrency primitives in addition to the ones provided by the language and "sync" and "sync/atomic" packages. ) FYI: a trend of singleflight https://github.com/golang/sync

FYI: a trend of singleflight ● According to https://dev.golang.org/release, internal/singleflight is going to delete and recommend x/sync/singleflight to use from 1.14. https://go-review.googlesource.com/c/go/+/174080/ https://github.com/golang/go/issues/31697

Introduction to Use Case 1

● This Use Case in net/lookup ○ LookupIPAddr calls together for lookups for the same host. ○ LookupIPAddr looks up host using the local resolver. Introduction to Use Case 1 https://github.com/golang/go/blob/release-branch.go1.13/src/net/lookup.go#L204

net/lookup.go https://github.com/golang/go/blob/release-branch.go1.13/src/net/lookup.go#L152 https://github.com/golang/go/blob/release-branch.go1.13/src/net/lookup.go#L237

Introduction to Use Case 2

Introduction to Use Case 2 ● This Use Case of the technical spec in Microservices ○ Client ■ Request the API of GetCatalogComponent to Microservice A ■ To get the recommended Catalog( ID:1 ) ■ To get Catalog inserted within 1 week. ○ Microservice A - BFF layer ■ GetCatalogComponent provides the recommended Catalog(ID:1) and the Catalog inserted within 1 week as a aggregator. ● Request to API of GetCatalog to Microservice B ● Request to API of ListCatalogs to Microservice B ○ Microservice B - Database layer ■ GetCatalog provides Catalog specified by using ID ■ ListCatalogs provides Catalog specified by using 1 weeks.

Microservice A - BFF Layer GetCatalogComponent Microservice B - Catalog Service HTTP/gRPC Use Case 2 - Overview (before) GetCatalog - id:1 ListCatalog GetCatalog - id:1 ListCatalog - between 7 days catalog client

Microservice A - BFF Layer GetCatalogComponent Microservice B - Catalog Service HTTP/gRPC Use Case 2 - Overview (after) GetCatalog - id:1 ListCatalog GetCatalog - id:1 ListCatalog - between 7 days catalog singleflight client

Conclusion

● Package singleflight provides a duplicate function call suppression mechanism. ● If you need to tune the API that requests the same resource, singleflight will be helpful. ● It seems to me that such as BFF in Microservices is easy to apply the use case by using singleflight. ● If you have the interests, please check the other use case of other products imported singleflight, https://godoc.org/golang.org/x/sync/singleflight?importers Conclusion

Thank you. Any Questions??