Any Real-World Experience Using Software Transactional Memory? [closed]

Question!

It seems that there has been a recent rising interest in STM (software transactional memory) frameworks and language extensions. Clojure in particular has an excellent implementation which uses MVCC (multi-version concurrency control) rather than a rolling commit log. GHC Haskell also has an extremely elegant STM monad which also allows transaction composition. Finally, so as to toot my own horn just a bit, I've recently implemented an STM framework for Scala which statically enforces reference restrictions.

All of these are interesting experiments, but they seem to be confined to that sphere alone (experimentation). So my question is: have any of you seen or used STM in the real world? If so, why? What sort of benefits did it bring? What about performance? (there seems to be a great deal of conflicting information on this point) Would you use STM again or would you prefer to use some other concurrency abstraction like actors?



Answers

We have implemented our entire system (in-memory database and runtime) on top of our own STM implementation in C. Prior to this, we had some log and lock based mechanism to deal with concurrency, but this was a pain to maintain. We are very happy with STM since we can treat every operation the same way. Almost all locks could be removed. We use STM now for almost anything at any size, we even have a memory manager implement on top.

The performance is fine but to speed things up we now developed a custom operating system in collaboration with ETH Zurich. The system natively supports transactional memory.

But there are some challenges caused by STM as well. Especially with larger transactions and hotspots that cause unnecessary transaction conflicts. If for example two transactions put an item into a linked list, an unnecessary conflict will occur that could have been avoided using a lock free data structure.

By : gtroxler


We, factis research GmbH, are using Haskell STM with GHC in production. Our server receives a stream of messages about new and modified "objects" from a clincal "data server", it transforms this event stream on the fly (by generating new objects, modifying objects, aggregating things, etc) and calculates which of these new objects should be synchronized to connected iPads. It also receives form inputs from iPads which are processed, merged with the "main stream" and also synchronized to the other iPads. We're using STM for all channels and mutable data structures that need to be shared between threads. Threads are very lightweight in Haskell so we can have lots of them without impacting performance (at the moment 5 per iPad connection). Building a large application is always a challenge and there were many lessons to be learned but we never had any problems with STM. It always worked as you'd naively expect. We had to do some serious performance tuning but STM was never a problem. (80% of the time we were trying to reduce short-lived allocations and overall memory usage.)

STM is one area where Haskell and the GHC runtime really shines. It's not just an experiment and not for toy programs only.

We're building a different component of our clincal system in Scala and have been using Actors so far, but we're really missing STM. If anybody has experience of what it's like to use one of the Scala STM implementations in production I'd love to hear from you. :-)



I'm currently using Akka in some PGAS systems research. Akka is a Scala library for developing scalable concurrent systems using Actors, STM, and built-in fault tolerance capabilities modeled after Erlang's "Let It Fail/Crash/Crater/ROFL" philosophy. Akka's STM implementation is supposedly built around a Scala port of Clojure's STM implementation. An overview of Akka's STM module can be found here.

By : Marc


This video can help you solving your question :)
By: admin