[ADR] Caching

docs/adr/0001-record-architecture-decisions.md

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+# 1. Record architecture decisions
+
+Date: 2021-10-05
+
+## Status
+
+Accepted
+
+## Context
+
+We need to record the architectural decisions made on this project.
+
+## Decision
+
+We will use Architecture Decision Records, as [described by Michael Nygard](http://thinkrelevance.com/blog/2011/11/15/documenting-architecture-decisions).
+
+## Consequences
+
+See Michael Nygard's article, linked above. For a lightweight ADR toolset, see Nat Pryce's [adr-tools](https://github.com/npryce/adr-tools).

docs/adr/0002-caching.md

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+# 2. Caching
+
+Date: 2021-10-05
+
+## Status
+
+Accepted
+
+## Context
+
+- Client always make requests to back-end to refresh the data, what put a lot of pressure on it.
+- User need to wait a long time to see the mailbox and email.
+
+## Decision
+
+- Caching the data with the [Hive](https://github.com/hivedb/hive) dependencies 
+Hive is a lightweight and blazing fast key-value database written in pure Dart. It support cross-platform: mobile, desktop and browser
+
+- `changes` method allows a client to efficiently update the state of data (Mailbox and Email)
+
+## Consequences
+
+- Minimizing the requests to the back-end 
+- Reducing the latency in the client
+
+## Follow up works
+
+- Pre-loading the bodies of the some latest unread messages