Vendor Take Home Interview Questions

Please include a working coded solution along with an explanation for choosing a certain approach.

Question:

You are tasked with designing and implementing an in-memory database that supports key-value storage and transactions, including operations like get(key), set(key, value), delete(key), start_transaction(), commit() and roll_back(). A user is able to start a transaction with start_transaction(). Then the user could use commit() to commit all changes in the current transaction, or use roll_back() to discard all changes in the current transaction. In addition, the database supports nested transactions, which means you are able to create a transaction within a transaction. In this question, you can assume there is no multithread access. Please refer to the examples section to get a better idea how the system works.

Task:

Your task is to implement the InMemoryDatabase Class that supports the above database's core functionality. For example, the class has an interface defined as below in Python. You should use GOLANG.

class InMemoryDatabase:
    def __init__(self):
        # Initialize the in-memory database

    def get(self, key):
        """
        Get the value associated with the given key.
        :param key: The key to retrieve.
        :return: The value associated with the key or None if the key does not exist.
        """

    def set(self, key, value):
        """
        Store a key-value pair in the database.
        :param key: The key to store.
        :param value: The value to associate with the key.
        :return: None
        """

    def delete(self, key):
        """
        Delete the key-value pair associated with the given key.
        :param key: The key to delete.
        :return: None
        """

    def start_transaction(self):
        """
        Start a new transaction. All operations within this transaction are isolated from others.
        :return: None
        """

    def commit(self):
        """
        Commit all changes made within the current transaction to the database.
        :return: None
        """

    def rollback(self):
        """
        Roll back all changes made within the current transaction and discard them.
        :return: None
        """ 

Examples

Example 1 for commit a transaction

db = InMemoryDatabase()
db.set("key1", "value1")
db.start_transaction()
db.set("key1", "value2")
db.commit()
db.get(“key1”)    -> Expect to get “value2”

Example 2 for roll_back().

db = InMemoryDatabase()
db.set("key1", "value1")
db.start_transaction()
db.get("key1")    -> Expect to get “value1”
db.set("key1", "value2")
db.get("key1")    -> Expect to get ”value2”
db.roll_back()
db.get(“key1”)    -> Expect to get “value1”

Example 3 for nested transactions

db = InMemoryDatabase()
db.set("key1", "value1")
db.start_transaction()
db.set("key1", "value2")
db.get("key1")    -> Expect to get ”value2”
db.start_transaction()
db.get("key1")    -> Expect to get ”value2”
db.delete(“key1“)
db.commit()
db.get(“key1”)    -> Expect to get None
db.commit()
db.get(“key1”)     -> Expect to get None

Example 4 for nested transactions with roll_back()

db = InMemoryDatabase()
db.set("key1", "value1")
db.start_transaction()
db.set("key1", "value2")
db.get("key1")    -> Expect to get ”value2”
db.start_transaction()
db.get("key1")    -> Expect to get ”value2”
db.delete(“key1“)
db.roll_back()
db.get(“key1”)    -> Expect to get “value2”
db.commit()
db.get(“key1”)     -> Expect to get “value2”