146 lines
6.5 KiB
Markdown
146 lines
6.5 KiB
Markdown
# Machi: a robust & reliable, distributed, highly available, large file store
|
|
|
|
[Travis-CI](http://travis-ci.org/basho/machi) :: 
|
|
|
|
Outline
|
|
|
|
1. [Why another file store?](#sec1)
|
|
2. [Where to learn more about Machi](#sec2)
|
|
3. [Development status summary](#sec3)
|
|
4. [Contributing to Machi's development](#sec4)
|
|
|
|
<a name="sec1">
|
|
## 1. Why another file store?
|
|
|
|
Our goal is a robust & reliable, distributed, highly available, large
|
|
file store. Such stores already exist, both in the open source world
|
|
and in the commercial world. Why reinvent the wheel? We believe
|
|
there are three reasons, ordered by decreasing rarity.
|
|
|
|
1. We want end-to-end checksums for all file data, from the initial
|
|
file writer to every file reader, anywhere, all the time.
|
|
2. We need flexibility to trade consistency for availability:
|
|
e.g. weak consistency in exchange for being available in cases
|
|
of partial system failure.
|
|
3. We want to manage file replicas in a way that's provably correct
|
|
and also easy to test.
|
|
|
|
Of all the file stores in the open source & commercial worlds, only
|
|
criteria #3 is a viable option. Or so we hope. Or we just don't
|
|
care, and if data gets lost or corrupted, then ... so be it.
|
|
|
|
If we have app use cases where availability is more important than
|
|
consistency, then systems that meet criteria #2 are also rare.
|
|
Most file stores provide only strong consistency and therefore
|
|
have unavoidable, unavailable behavior when parts of the system
|
|
fail.
|
|
What if we want a file store that is always available to write new
|
|
file data and attempts best-effort file reads?
|
|
|
|
If we really do care about data loss and/or data corruption, then we
|
|
really want both #3 and #1. Unfortunately, systems that meet
|
|
criteria #1 are _very rare_.
|
|
Why? This is 2015. We have decades of research that shows
|
|
that computer hardware can (and
|
|
indeed does) corrupt data at nearly every level of the modern
|
|
client/server application stack. Systems with end-to-end data
|
|
corruption detection should be ubiquitous today. Alas, they are not.
|
|
Machi is an effort to change the deplorable state of the world, one
|
|
Erlang function at a time.
|
|
|
|
<a name="sec2">
|
|
## 2. Where to learn more about Machi
|
|
|
|
The two major design documents for Machi are now mostly stable.
|
|
Please see the [doc](./doc) directory's [README](./doc) for details.
|
|
|
|
We also have a
|
|
[Frequently Asked Questions (FAQ) list](./FAQ.md).
|
|
|
|
Scott recently (November 2015) gave a presentation at the
|
|
[RICON 2015 conference](http://ricon.io) about one of the techniques
|
|
used by Machi; "Managing Chain Replication Metadata with
|
|
Humming Consensus" is available online now.
|
|
* [slides (PDF format)](http://ricon.io/speakers/slides/Scott_Fritchie_Ricon_2015.pdf)
|
|
* [video](https://www.youtube.com/watch?v=yR5kHL1bu1Q)
|
|
|
|
<a name="sec3">
|
|
## 3. Development status summary
|
|
|
|
Mid-December 2015: work is underway.
|
|
|
|
* In progress:
|
|
* Code refactoring: metadata management using
|
|
[ELevelDB](https://github.com/basho/eleveldb)
|
|
* File repair using file-centric, Merkle-style hash tree.
|
|
* Server-side socket handling is now performed by
|
|
[ranch](https://github.com/ninenines/ranch)
|
|
* QuickCheck tests for file repair correctness
|
|
* 2015-12-15: The EUnit test `machi_ap_repair_eqc` is
|
|
currently failing occasionally because it (correctly) detects
|
|
double-write errors. Double-write errors will be eliminated
|
|
when the ELevelDB integration work is complete.
|
|
* The `make stage` and `make release` commands can be used to
|
|
create a primitive "package". Use `./rel/machi/bin/machi console`
|
|
to start the Machi app in interactive mode. Substitute the word
|
|
`start` instead of console to start Machi in background/daemon
|
|
mode. The `./rel/machi/bin/machi` command without any arguments
|
|
will give a short usage summary.
|
|
* Chain Replication management using the Humming Consensus
|
|
algorithm to manage chain state is stable.
|
|
* ... with the caveat that it runs very well in a very harsh
|
|
and unforgiving network partition simulator but has not run
|
|
much yet in the real world.
|
|
* All Machi client/server protocols are based on
|
|
[Protocol Buffers](https://developers.google.com/protocol-buffers/docs/overview).
|
|
* The current specification for Machi's protocols can be found at
|
|
[https://github.com/basho/machi/blob/master/src/machi.proto](https://github.com/basho/machi/blob/master/src/machi.proto).
|
|
* The Machi PB protocol is not yet stable. Expect change!
|
|
* The Erlang language client implementation of the high-level
|
|
protocol flavor is brittle (e.g., little error handling yet).
|
|
|
|
If you would like to run the network partition simulator
|
|
mentioned in the Ricon 2015 presentation about Humming Consensus,
|
|
please see the
|
|
[partition simulator convergence test doc.](./doc/machi_chain_manager1_converge_demo.md)
|
|
|
|
If you'd like to work on a protocol such as Thrift, UBF,
|
|
msgpack over UDP, or some other protocol, let us know by
|
|
[opening an issue to discuss it](./issues/new).
|
|
|
|
<a name="sec4">
|
|
## 4. Contributing to Machi's development
|
|
|
|
### 4.1 License
|
|
|
|
Basho Technologies, Inc. as committed to licensing all work for Machi
|
|
under the
|
|
[Apache Public License version 2](./LICENSE). All authors of source code
|
|
and documentation who agree with these licensing terms are welcome to
|
|
contribute their ideas in any form: suggested design or features,
|
|
documentation, and source code.
|
|
|
|
Machi is still a very young project within Basho, with a small team of
|
|
developers; please bear with us as we grow out of "toddler" stage into
|
|
a more mature open source software project.
|
|
We invite all contributors to review the
|
|
[CONTRIBUTING.md](./CONTRIBUTING.md) document for guidelines for
|
|
working with the Basho development team.
|
|
|
|
### 4.2 Development environment requirements
|
|
|
|
All development to date has been done with Erlang/OTP version 17 on OS
|
|
X. The only known limitations for using R16 are minor type
|
|
specification difference between R16 and 17, but we strongly suggest
|
|
continuing development using version 17.
|
|
|
|
We also assume that you have the standard UNIX/Linux developers
|
|
tool chain for C and C++ applications. Specifically, we assume `make`
|
|
is available. The utility used to compile the Machi source code,
|
|
`rebar`, is pre-compiled and included in the repo.
|
|
|
|
Machi has a dependency on the
|
|
[ELevelDB](https://github.com/basho/eleveldb) library. ELevelDB only
|
|
supports UNIX/Linux OSes and 64-bit versions of Erlang/OTP only; we
|
|
apologize to Windows-based and 32-bit-based Erlang developers for this
|
|
restriction.
|