A memcached-compatible clone written in rust

Features:

• Aside from what's listed in Missing below, we support all memcached commands and are fully compatible

Missing:

• binary protocol
• stats
• UDP
• unix sockets
• delete with expires (memcached dropped this support in 1.4)
• flush_all with expires
• verbosity is recognised but ignored
• SASL

Performance

rustcache is about half as fast as memcached according to memslap:

rustcached:

$ memslap --servers=localhost:11211 --test=set --concurrency=10 --debug --execute-number=10000 --flag --flush
    Threads connecting to servers 10
    Took 3.145 seconds to load data
$ memslap --servers=localhost:11211 --test=get --concurrency=10 --debug --execute-number=10000 --flag --flush
    Threads connecting to servers 10
    Took 4.976 seconds to read data

memcached:

$ memslap --servers=localhost:11212 --test=set --concurrency=10 --debug --execute-number=10000 --flag --flush
    Threads connecting to servers 10
    Took 2.736 seconds to load data
$ memslap --servers=localhost:11212 --test=get --concurrency=10 --debug --execute-number=10000 --flag --flush
    Threads connecting to servers 10
    Took 3.933 seconds to read data

Code organisation:

• cmd.rs: control starts here, command line arguments parsed, and the server started
• store.rs: houses the memcached application logic (e.g. what does "add" mean and how do I apply it?)
• lru.rs: the LRU cache
• parser.rs: protocol parsing
• server.rs: socket handling and response writing

Todo:

• We're using the default rust allocator (jemalloc) for everything, instead of a slab allocator like memcached
• you can exhaust memory in the parser with an unlimited key/value length
• you can't set values larger than the memcached length limits, but you can append/prepend past them
• We copy a lot of stuff around right now that we don't have to, especially in the response builder
• lru.rs uses Arc<T> but there's probably a way to just use Rc<T> when we go single-threaded

Future features:

• we use LRU right now like memcached does, but I want to try ARC in a real environment
• eager deletion of expired items during idle periods