#cpp11-memcached This is a toy memcached server that simply supports set and get requests, written as an opportunity to write some more c++11.
##Building Requirements:
- C++11 compatible compiler
- CMake
- Boost
- Node.js (optional, for running some of the local tests)
mkdir build && cd buid
cmake ..
make
./main
For Boost & Cmake, you can install it on OSX with brew install boost cmake and on Ubuntu with sudo aptitude install cmake libboost-all-dev.
###CAS Field The CAS field is used to signal atomicity. From the memcached spec, section 4.3 "Set, Add, Replace":
If the Data Version Check (CAS) is nonzero, the requested operation
MUST only succeed if the item exists and has a CAS value identical to
the provided value.
CAS is short for Compare And Swap, a common atomic operation that only updates a value if the writer has the most up to date value. For example, if thread A writes to a location, then thread B writes to the same location, thread A's subsequent CAS operation will fail.
###Tradeoffs
- This code assumes all key value pairs can fit into memory on this machine. This doesn't scale well beyond a single machine. Moving to a distributed message queue might be better, but adds complexity in keeping all caches coherent.
- One thread is spawned per connection. This adds latency as the thread is being spawned, and can easily use up system resources in a DoS attack. Instead, a thread pool should be used.
- Connections are handled synchronously. This hurts throughput, but makes the code slightly simpler. Boost asio has support for async.
- All threads share a key value store. Shared memory is juggling razors. Also, I simply wrap access to the key value store in a mutex. A thread must acquire the mutex once for a set operation and twice for a get operation. The use of a properly programmed concurrent map would be better, like from libcds or even the basic example from C++ Concurrency in Action: Practical Multithreading.
###Formatting
Each C++ source and header is run through clang-format -i find . -name '*.cpp'`.