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From Eric Evans <eev...@rackspace.com>
Subject NoSQL, YesCQL?
Date Thu, 28 Oct 2010 20:40:07 GMT

I don't know about everyone else, but I've been pretty dissatisfied with
our API situation for some time.

I used to be of the opinion that The Problem was Thrift and The Answer
was Avro.  I do still prefer Avro over Thrift as dependencies go, but
I've come to the conclusion that the real problem has more to do with
the object-oriented RPC pattern that both share in common.

I used to think this was a necessary burden in order to expose the full
power of our query API in a client agnostic manner, and that it was the
job of third-party libraries to wrap this layer to create stable
idiomatic interfaces.

And, I used to think a vibrant ecosystem of these idiomatic libraries
would emerge, but it hasn't.  Truth is we've seen quite a bit of
proliferation, and very little critical mass. 

This shouldn't be construed as criticism levied against library
maintainers, on the contrary, I think they've done an amazing job all
things considered.  But in my opinion, our RPC interfaces push way too
many implementation details client-side, making them brittle and
unstable.  This results in unnecessarily complex libraries that are
forced to move in lock-step with Cassandra releases, that are never
backward compatible, and which are consistently broken during our
development cycle.  I think we can provide client maintainers and users
with a better experience than this.

One solution to this is to implement a server-side query language, with
simple language drivers that manage all of the common functionality in a
consistent way (statement preparation, connection pooling, etc).
Library maintainers would then build their idiomatic interfaces on top
of these, (and I imagine, remove a metric crap-ton of code in the
process).

To this end I've been playing with exactly that.  I have enough to do
simple reads and writes, and I have stubbed out drivers for Java and
Python.  I'm seeking community feedback to gauge interest, and to
satisfy the much needed desire to bike-shed. :)

http://github.com/eevans/cassandra/tree/CQL

You need to be sure you're checking out the "CQL" branch.

This is implemented in the Avro interface so you'll need to pass the -a
flag when launching the daemon.

It is far from complete, and is surely quite buggy at this stage, take
it as a preview or demonstration; it's meant to be a starting point for
discussion. 

There is a bit of documentation on the syntax, you can see that here:
http://github.com/eevans/cassandra/blob/CQL/doc/cql/CQL.textile

There are some system tests in test/system/test_cql.py that should give
you the basic idea, but assuming you have the Avro Python module
installed you should be able to just...

$ cd drivers/py
$ python
>>> import cql
>>> conn = cql.Connection('Keyspace1', 'localhost', 9160)
>>> conn.execute('UPDATE Standard1 WITH ROW("k", COL("c", "hello!"));')
>>> print conn.execute('SELECT FROM Standard1 WHERE KEY = "k"')
[{u'columns': [{u'timestamp': 1288297508761L, u'name': 'c', u'value':
'hello!', u'ttl': None}], u'key': 'k'}]
>>>


I've been chewing on all of this for a while so I'm brimming with ideas,
but I'll let the dust settle on this email before going any further. :)

Thoughts?



P.S. Dear Cliff Moon, I apologize.  You were right.

-- 
Eric Evans
eevans@rackspace.com





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