In this week’s podcast, QCon chair Wesley Reisz talks to Keith Adams, chief architect at Slack. Prior he was an engineer at Facebook where he worked on the search type live backend, and is well-known for the HipHop VM [hhvm.com]. Adams presented How Slack Works at QCon SanFrancisco 2016.

Why listen to this podcast:

- Group messaging succeeds when it feels like a place for members to gather, rather than just a tool

- Having opt-in group membership scales better than having to define a group on the fly, like a mailing list instead of individually adding people to a mail

- Choosing availability over consistency is sometimes the right choice for particular use cases

- Consistency can be recovered after the fact with custom conflict resolution tools

- Latency is important and can be solved by having proxies or edge applications closer to the user

Notes and links can be found on: http://bit.ly/keith-adams

3m:30s Voice and video interactions are impacted by latency; the same is true of messaging clients

4m:00s The user interface can provide indications of presence, through avatars indicating availability and typing indicators

4m:15s Latency is important; sometimes the difference is between 100ms and 200ms so the message channel monitors ping timeout between server and client

4m:40s 99th percentile is less than 100ms ping time

5m:15s If the 99th percentile is more than 100ms then it may be server based, such as needing to tune the Java GC

5m:25s Network conditions of the mobile clients are highly variable 

6m:20s Mobile clients can suffer intermittent connectivity

More on this:

Quick scan our curated show notes on InfoQ. http://bit.ly/keith-adams

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