nearmap.com Go Test

Welcome to the Nearmap Go test. The purpose of this assignment is to test your familiarity with Go, distributed systems concepts and unit testing.

Background

The source code that you are given is a very simple imitation of a key/value store:

• Database represents a client to the central store that takes a long time (500ms) to store and retrieve data.
• DistributedCache represents a client to the distributed cache (Redis for example) that takes much less time to turn around (100ms to store or retrieve).

This scenario is a simplified example of a typical high performance server cluster with a database, a distributed cache and multiple worker nodes.

Assumptions

After startup:

• Data in Database never changes and can be cached forever.
• If Database.Value() returns nil for a key, the requested data item does not exist and will never exist.
• DistributedCache is initially empty.

Task

Complete the 2 parts below and submit the solution. If the solution is incomplete, please state what hasn't been finished and outline how you are planning on solving it.

• Provided code can be modified at will.
• The whole solution must build with no errors.

Part 1

Create an implementation for the DataSource interface to create a mechanism to retrieve data from Database with lowest possible latency. An example LocalDataSource struct has been provided as a start.

For a frequently-requested item your DataSource.Value() implementation should have a better response time than the distributed cache store (ie < 100ms).

• The user of the DataSource interface must not have to deal with thread synchronisation.
• Write unit tests for the new DataSource implementation (only), and ensure all tests pass.
• The solution should aim to minimise calls to the database.
• Limit your use of libraries to the Go standard library only.

Part 2

Complete main() to test your DataSource implementation; it must:

• Populate Database with the following data at startup:

    | key          | value         |
    --------------------------------
    | key0         | value0        |
    | key1         | value1        |
    | key2         | value2        |
    | key3         | value3        |
    | key4         | value4        |
    | key5         | value5        |
    | key6         | value6        |
    | key7         | value7        |
    | key8         | value8        |
    | key9         | value9        |

• Use 10 goroutines (simulating separate threads on a single worker node) each making 50 consecutive requests for a random key in the range (key0-key9). I.e. there should be a total of 500 requests.
• For each request, print the 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

• DO NOT publicly fork this repository or create pull requests on it as we don't want other candidates to see your solution.
• Please submit your solution as per instructions provided in the correspondence.