a system design question

Design a service that keeps track of mobile users as they check in at different locations. This service will get informed of each check-in in real time (a user/location pair) and must be able to answer the following queries in real time:

1. Where is user U right now?
2. What users are at location L right now?

The following requirements apply:

1. A user can only be at one location at a time. If user U checks in at location X and then at location Y, they are no longer at location X.

2. A check-in only valid for at most 2 hours. If user U checks in at location X and then does nothing for 2 hours, they are no longer at location X.

The service should have durable enough storage that you can restart it without losing all of your data It should not store everything in memory.

what kind of DB will you use and how data will be organized and any indexes. If storage is spread out over multiple databases(locations), how is that done?

scalability/availability consideration, how will be distribute multiple servers. what happens when the traffic goes 10x all of sudden. What happens if one of the server goes down.

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直接搞个geohash就好了吧。用户每个几秒给server 发个心跳就好了。

scredwood 发表于 2017-6-28 10:20
直接搞个geohash就好了吧。用户每个几秒给server 发个心跳就好了。

server会顶不住压力的，最好是用户换location的时候再communicate，判断location在mobile客户端本地进行