I've implemented in the package org.apache.activemq.artemis.core.io.mapped a new memory mapped SequentialFile implementation to support fast write/read operations for OSs that cannot use libaio or need RAM access performances on standard Files.
The implementation is not thread-safe (it is needed?) and needs more buffer checks (or a complex implementation). I'm using the Netty's PlatformDependent class to perform bulk copy without safepoint's poll issues.
The implementation is simple but it's good as a proof of concept to compare it against the others: i' ve added a coordinated-omission performance test to measure the latency of a directWrite + OS jitter.
The write tests show performances typical of memory mapped file: quoting from Peter Lawrey "for burst of up to 10% of the main memory, it can sustain rates of 1 - 3 GB/second written. e.g. A laptop with 8 GB of memory might handle bursts of 800 MB at a rate of 1 GB per second. A server with 64 GB of memory might handle a burst of 6.5 GB at a rate of 3 GB per second".
I want to improve the quality of the implementation by:
1- enforcing the original SequenceFile contract
2- replacing synchronized reads/writes with lock-free versions
3- replacing the EventExecutor with a Lock-Free (even wait-free) Array Queue + EventLoop's poller
4- addressing all the False-Sharing issues around all the AtomicLong instances used
5- reducing the garbage produced for the fast paths to 0
[6- expose try methods to allow direct flow control]
[7- replacing the Semaphore based rate limiter with a lock free one]
That's are all proposals, what do you think about it?