This is a simple key valye store

This is simple implementation of a key value store that can be used to store keys in a SSD.

Usage

Usage: key_value_store_ssd [OPTIONS]

Options:

-p, --port <PORT>  The port to listen on
    --path <PATH>  The path to the key-value store [default: ./ssd]
-h, --help         Print help
-V, --version      Print version

The path needs to exist before the app is started.

API Endpoints

The store supports the following Apis. All apis require a POST request with a Json body and need to set Content-Type: Application/Json header

/insert

This api will create a new key or fail if one exists

{
    "key":"key_name",
    "value":"key_value"
}

or it can be an array of multiple keys values

[
    {
        "key" : "key_1_name",
        "value" : "key_1_value"
    },
    {
        "key" : "key_2_name",
        "value" : "key_2_value",
    }
]

The api will return a json array depending upon the request with

{
    "key" : "key_name",
    "modified" : "true or false depending on the success or failure"
}

/update

This works like the /insert endpoint with the addition of creating a file if it does not exist and updating if it exists.

/get

This api will get the values of keys

[
    {
        "key":"key_name"
    }
]

or it can be an array of multiple keys values

[
    {
        "key" : "key_1_name"
    },
    {
        "key" : "key_2_name"
    }
]

The api will return a Json array depending upon the request with

[
    {
    "key" : "key_name",
    "value" : "key_value",
    "found" : "true or false depending on if the key was found"
    }
]

or

[
    {
        "key" : "key_1_name",
        "value" : "key_1_value",
        "found" : "true"
    },
    {
        "key" : "key_2_name",
        "value" : "",
        "found" : "false"
    }
]

The value of keys not present in the store will be an empty string. The found indicates if the key was found or not in the store.

/delete

This api will delete keys from the store

{
    "key":"key_name"
}

or it can be an array of multiple keys values

[
    {
        "key" : "key_1_name"
    },
    {
        "key" : "key_2_name"
    }
]

The api will return a Json or Json array depending upon the request with

[
    {
        "key" : "key_name",
        "deleted" : "true or false depending on if the key was found"
    }
]

or

[
    {
        "key" : "key_1_name",
        "deleted" : "true"
    },
    {
        "key" : "key_2_name",
        "deleted" : "true"
    }
]

For safety/security keys deleted are always true even if the key is not found

/key

This api will get a list of key mathcing a prefix provided in the body

{
    "prefix":"key"
}

Unlike the other endpoind this does not take an array but returns an array. The above example will match all keys starting with key

[
    {
        "key":"key_1_name"
    },
    {
        "key":"key_2_name"
    },
    {
        "key":"key_3_name"
        }
]

It will return an empty array is nothing is found

Sample Test Calls

insert

curl --location 'http://localhost:8080/insert' \
--header 'Content-Type: application/json' \
--data '[
    {
    "key":"key_1_name",
    "value":"key_1_value"
    },
    {
    "key":"key_2_name",
    "value":"key_2_value"
    },
    {
    "key":"key_3_name",
    "value":"key_3_value"
    }
]'

On success this will resturn

[
    {"key":"key_1_name", "modified": "true"},
    {"key":"key_2_name", "modified": "true"},
    {"key":"key_3_name", "modified": "true"}
]

get

curl --location 'http://localhost:8080/get' \
--header 'Content-Type: application/json' \
--data '
    [
        {"key":"key_1_name"},
        {"key":"key_2_name"},
        {"key":"key_non_existing"}
    ]
'

The above example returns

[
    {"key":"key_1_name", "value":"key_1_value" "found": "true"},
    {"key":"key_2_name", "value":"", "found": "false"},
    {"key":"key_non_existing", "value":"", "found": "false"}]

The key_non_existing has a found=false indication that this value was not found.

#keys

curl --location 'http://localhost:8080/keys' \
--header 'Content-Type: application/json' \
--data '{
    "prefix": "key"
}'

The above example will return keys mathing key*

[
    {"key":"key_1_name"},
    {"key":"key_3_name"},
    {"key":"key_name"}
]

delete

curl --location 'http://localhost:8080/delete' \
--header 'Content-Type: application/json' \
--data '
    [
        {"key":"key_1_name"},
        {"key":"key_2_name"},
        {"key":"key_nonexisting"}
    ]

It will delete the 3 files and result something like

    {"key":key_1_name, "deleted": "true"},{"key":key_2_name, "deleted": "true"},{"key":key_nonexisting, "deleted": "true"}

Excluded Tests

The tests are not included because this is writing to files and it can quickly destroy regular ssd.

Future Enhancements

• The file system needs to be injected and decoupled from the system to be able to mock it correctly. That will help add tests.
• The code for get/insert/delete is similar except the returned Json and the actual function of the FileSystemGateway called. It can be refactored into same function with different call function as higer order function or simple if logic
• The locking mechanism is simple, it create X amount of locks and the lock bucket is based on the size of the key. It can be imporved by hasing and adding a larger bucket. A hashmap of locks for each key separately might be too memory heavy and will need additional functionality for pruning and separate locks for making the hash map itself thread safe. There are some libraries available for thread safe hashmap.
• The cache is built in the http server. It can be moved to the file system gateway to keep the complexity out of server logic and let the file system gateway handle the cache mechanism.
• The current cache is an external library. A simple hash-map can also be used if it is made thread-safe.