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nearmap.com Technical Test

Welcome to nearmap.com technical test. The purpose of this assignment is to test your familiarity with C#, distributed systems concepts, performance benchmarking and TDD.

Background

The source code that you are given is a very simple imitation of a name/value store. DatabaseStore is the canonical data store that takes a while (50 ms) to store and retrieve data. DistributedCacheStore is an interface to a distributed cache that takes much less time to turn around - 5 ms. This scenario is a simplified example of a typical high performance server cluster with a database, a distributed cache and multiple worker nodes.

Assumptions

  • Data in the canonical store (database) never changes and can be cached forever.
  • Data is never written to the canonical store (database), apart from during the startup.
  • If GetValue method returns null, the request data item does not exist and will never exist.
  • The solution should start with the distributed cache empty.
  • Provided code can be modified at will.
  • The aim of the test is to produce the simplest working solution to the problem. As such you are at liberty to choose any .NET framework classes.

Task

  • The objective is to create a data retrival mechanism with lowest possible latency by implementing the IDataSource interface.
  • The solution should have a better response time than that one of distributed cache for a frequently requested item, i.e. response time should be faster than 5ms.
  • The solution should have unit tests for all new functionality.
  • The user of the IDataStore interface must not have to deal with thread synchronisation.
  • The database should be populated with the following data on startup:
    | key          | value         |
    --------------------------------
    | key0         | value0        |
    | key1         | value1        |
    | key2         | value2        |
    | key3         | value3        |
    | key4         | value4        |
    | key5         | value5        |
    | key6         | value6        |
    | key7         | value7        |
    | key8         | value8        |
    | key9         | value9        |
  • The solution must have 10 threads each making 50 consecutive requests for a random key in the range (key0-key9). I.e. there would a total of 500 requests.
  • The solution must print the managed ThreadId, requested key name, returned value, time to complete that request, similar to the following example:
    [1] Request 'key1', response 'value1', time: 50.05 ms
    [2] Request 'key2', response 'value2', time: 50.05 ms

Submission instructions

  • The whole Visual Studio solution must build with no errors.
  • If the solution is incomplete, please state what hasn't been finished and outline how you are planning on solving it.
  • DO NOT send pull requests against this repository because we don't want other candidates to see your solution.