PyMemDB - A Simple In-Memory Key-Value Store

PyMemDB is a lightweight, in-memory key-value store written in Python. Designed as a simple implementation of a database, it stores data in memory and uses the RESP protocol (similar to Redis) for communication with clients.

Key Features

• 12 Supported Commands: PyMemDB supports 12 essential commands, including common operations like GET, SET, INCR, and list operations such as LPUSH and RPUSH. These commands provide the functionality needed for basic key-value storage and list management.

• I/O Multiplexing: Leveraging asynchronous programming with asyncio, PyMemDB uses efficient I/O multiplexing, allowing it to handle multiple client connections concurrently, achieving improved performance on operations.

• Append Only File (AOF) Persistence: PyMemDB includes an optional AOF persistence mode. When enabled, it logs each write operation to a file in real-time, providing basic durability by allowing data to be restored if the server restarts. However, AOF must be explicitly enabled.

Limitations

While PyMemDB provides in-memory data storage, it does not offer full persistence. Without AOF enabled, data exists only in memory and will be lost when the program terminates.

Use Cases

PyMemDB can be useful for:

• Development and testing of key-value storage solutions
• Learning and experimentation with RESP-based communication and basic in-memory storage mechanics

For more details on starting the server, see the section on Starting the PyMemDB Server.

Installation

To install PyMemDB, you need to have Poetry installed on your system. Poetry is a dependency management and packaging tool for Python.

If you don't have Poetry installed, you can follow the installation instructions provided in the Poetry documentation.

Once you have Poetry installed, navigate to the directory where you have the pyproject.toml file for PyMemDB. Run the following commands to install the dependencies:

pip install poetry
poetry shell

This will create a virtual environment and install all the required dependencies for PyMemDB.

Usage

PyMemDB provides several commands that you can use. Here are the available commands:

• run-cli: Run the PyMemDB command-line interface.
• run-server: Run the PyMemDB server.
• run-async-server: Run the PyMemDB asynchronous server.
• run-server-with-debugger: Run the PyMemDB server with a debugger attached.
• run-async-server-with-debugger: Run the PyMemDB asynchronous server with a debugger attached.
• run-cli-with-debugger: Run the PyMemDB command-line interface with a debugger attached.
• run-test-services: Run the test services using Docker Compose.
• run-all-tests: Run all the tests for PyMemDB.
• pytest-debug: Run the tests with debugging enabled.
• run-server-with-profiler: Run the PyMemDB asynchronous server with a profiler enabled.
• run-lint: Run the linter to check the code for style and syntax errors.
• run-formatter: Run the code formatter to format the code according to the project's style guide.

To execute these commands, use the following format: poe run <command>.

Available Commands

1. ping
   Usage: ping
   Sends a ping to the server to check if it is responsive. The server responds with "PONG."

2. echo
   Usage: echo <message>
   Returns the provided message back to the client. Useful for debugging or testing connectivity.

3. get
   Usage: get <key>
   Retrieves the value associated with the specified key from the key-value store. Returns nil if the key does not exist.

4. set
   Usage: set <key> <value>
   Stores the specified value under the given key in the key-value store. If the key already exists, its value is updated.

5. exists
   Usage: exists <key>
   Checks if a specific key exists in the store. Returns 1 if the key exists and 0 otherwise.

6. del
   Usage: del <key>
   Deletes the key-value pair associated with the specified key from the store. Returns the number of keys removed.

7. incr
   Usage: incr <key>
   Increments the integer value of the specified key by 1. If the key does not exist, it is initialized to 0 before incrementing. Returns the new value.

8. decr
   Usage: decr <key>
   Decrements the integer value of the specified key by 1. If the key does not exist, it is initialized to 0 before decrementing. Returns the new value.

9. rpush
   Usage: rpush <key> <value>
   Pushes the specified value to the right end of a list associated with the given key. If the key does not exist, a new list is created.

10. lpush
    Usage: lpush <key> <value>
    Pushes the specified value to the left end of a list associated with the given key. If the key does not exist, a new list is created.

11. lrange
    Usage: lrange <key> <start> <stop>
    Retrieves a range of values from the list associated with the specified key, starting from start to stop. Returns an empty list if the key does not exist or is not a list.

Starting the PyMemDB Server

To start the PyMemDB server, you can use the following command-line arguments to configure it based on your needs:

poe run-async-server [--port PORT] [--host HOST] [--appendonly BOOL] [--startexpiryloop BOOL] [--restoredb BOOL] [--aofpath PATH]

Contributing

Contributions are welcome! If you have ideas for new features, optimizations, or improvements, feel free to submit a pull request or open an issue on GitHub.

License

PyMemDB is open-source software licensed under the MIT License. See the LICENSE file for more information.

Get Started

Explore the code and try out PyMemDB by visiting the GitHub Repository.

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Thank you for using PyMemDB! Your support and feedback are invaluable to making this project better. If you find it helpful or have suggestions, don’t hesitate to connect.