Neks

A dead simple key/value server

Neks is an in-memory networked key/value server written in ~200 lines of Haskell.

It is intended to be very easy to modify.

Features

Very simple
Pretty fast (>1M transactions per second is easy, see Benchmark)
Highly concurrent
Atomic transactions (e.g. atomic read-and-swap)
Optional disk persistence (with atomic snapshotting)

To install using Cabal:

cabal install neks
NeksServer <opt-args>
NeksClient <args>

To build and run from source (recommended):

cabal sandbox init
cabal install --only-dependencies
cabal run NeksServer
cabal run NeksClient -- <args>

or, with dependencies installed:

ghc -O2 -threaded Network/Neks/NeksServer.hs
ghc -O2 -threaded Network/Neks/NeksClient.hs
./Network/Neks/NeksServer +RTS -N<number of cores>
./Network/Neks/NeksClient <args>

To run the Python client:

python3 Client.py

To view instructions:

NeksServer --help
NeksClient --help

Benchmark:

The server and client run on two cores. The client runs

50 threads
200 requests per thread
50 reads and 50 writes per request

Speed depends on latency and bandwidth. Here's what I get on my home machines:

Avg. Latency	Transactions / Second
.1ms (localhost)	1,150,000
.3ms (ethernet)	1,100,000
3.5ms (wireless)	750,000

Protocol:

All network encoding is done using msgpack.

Messages are preceded by the length of the message, transmitted as a 64-bit big-endian unsigned integer.

The client sends requests to the server, and the server responds with the results of the requests.

There are 4 kinds of requests:

Requests to Get key K. These are formatted as [0, K]. The server sends a response.
Requests to Set key K to value V. These are formatted as [1, K, V]. The server does not send a response.
Requests to Delete key K. These are formatted as [2, K]. The server does not send a response.
Requests to Atomically evaluate a list of requests R. This is formatted as [3, R]. The server sends the response as if all requests in R had been evaluated normally.

There are 2 kinds of responses:

Response that the value V for requested key K was found. This is formatted as [-1, V].
Response that the value for requested key K was not found. This is formatted as [-2].

Example conversation:

Client: <message length>[[1,"status","OK"],[0,"Jim"],[0,"Dwight"]]
Server: <message length>[[-1,"Halpert"],[-1,"Schrute"]]

wyager/Neks