Simple Key-value Database with Go

This is a basic implementation of key-value database that written in Go language.

The project lies under understanding key-value databases. It's not a production-ready code or not an alternative project to Redis or Memcache.

It's a good kickstart project to understand the following

• Use network-level communication. Parse and send binary json over TCP.
• Service to multiples clients at the same time
• Mutex locks
• Parse the received flags
• IO Basics
• Implementation of the protocol
• Use built-in packages in Go. (The program does not require any 3th party package.)

About Specifications

Specification of the program has sourced from hipo/backend-challenges/kvdb

Clients

Clients should open a TTL connection to the port that the program runs. All communication (sending-receiving) will be in binary formatted JSON. Here is a example client code that written in Go.

Commands

There are eight commands to operate the database to do CRUD.

SET

Creates a key-value pair in the database. If the key exists already in the database, the newest value will rewrite on key.

{
    "command": "SET",
    "args": {
        "key": "foo",
        "value": "some string value"
    }
}

This commands in binary create a key that named foo and a value that content with some string value

if you'll pass an argument that named ttl, you define a TTL property to the key that defined. Your value will expire in seconds that defined in ttl value. You can change that wish with using EXPIRE as a command. Refer: EXPIRE The database only holds string values. If you use DECR or INCR commands the database will try to format your value in float or int before executing your command.

Also SET command calculates the database size before the add your request. If your key-value pair will make overflow the database size, your request will be deferred. The database has a max size or it can absolut database that makes it unlimited. You can change it with -max-mem-size argument. The argument changes the database maximum size in bytes, zero value means no-limits.

GET

Get a value that related with received key. If the key doesn't exist in the database response error message.

{
    "command": "GET",
    "args": {
        "key": "foo"
    }
}

Reflects the value in result array in the response.

Delete

Deletes the value related with the received key. Always return OK response.

{
    "command": "DELETE",
    "args": {
        "key": "foo"
    }
}

INCR

The method increases once the value related with the received key. The holding value could be parsable to float64 or int otherwise throws parse error.

{
    "command": "INCR",
    "args": {
        "key": "x"
    }
}

DECR

Works as the same as INCR method. But decreases once the value.

{
    "command": "DECR",
    "args": {
        "key": "x"
    }
}

EXPIRE

Changes or sets TTL value the received key. The expire defines the expiration in seconds.

{
    "command": "EXPIRE",
    "args": {
        "key": "foo",
        "ttl": "60"
    }
}

TTL

TTL command responds to the remaining seconds to expire key that received.

{
    "command": "TTL",
    "args": {
        "key": "foo"
    }
}

PING

Just a basic implementation to test the connection. Reflects PONG data.

{
    "command": "PING"
}

go run main.go --help
  -detach
        Prints nothing to screen
  -file string
        Refers to database's location on the disk. Should be existed file.
  -max-mem-size int
        Sets the maximum size of database. Server does not accepts new entries while maximum size is hanging. Default 0 means no limits.
  -panics
        Shows panics.
  -persist-to-disk int
        Server stores the database in every given minutes. (default 60)
  -port string
        Sets serving port. The given port number should be free for communication (default "6379")
  -refresh-rate int
        Sets screen refresh rate in seconds. (default 1)