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From Dave Viner <davevi...@pobox.com>
Subject Re: non blocking Cassandra with Tornado
Date Tue, 27 Jul 2010 15:51:28 GMT
FWIW - I think this is actually more of a question about Thrift than about
Cassandra.  If I understand you correctly, you're looking for a async
client.  Cassandra "lives" on the other side of the thrift service.  So, you
need a client that can speak Thrift asynchronously.

You might check out the new async Thrift client in Java for inspiration:

http://blog.rapleaf.com/dev/2010/06/23/fully-async-thrift-client-in-java/

Or, even better, port the Thrift async client to work for python and other
languages.

Dave Viner


On Tue, Jul 27, 2010 at 8:44 AM, Peter Schuller <peter.schuller@infidyne.com
> wrote:

> > The idea is rather than calling a cassandra client function like
> > get_slice(), call the send_get_slice() then have a non blocking wait on
> the
> > socket thrift is using, then call recv_get_slice().
>
> (disclaimer: I've never used tornado)
>
> Without looking at the generated thrift code, this sounds dangerous.
> What happens if send_get_slice() blocks? What happens if
> recv_get_slice() has to block because you didn't happen to receive the
> response in one packet?
>
> Normally you're either doing blocking code or callback oriented
> reactive code. It sounds like you're trying to use blocking calls in a
> non-blocking context under the assumption that readable data on the
> socket means the entire response is readable, and that the socket
> being writable means that the entire request can be written without
> blocking. This might seems to work and you may not block, or block
> only briefly. Until, for example, a TCP connection stalls and your
> entire event loop hangs due to a blocking read.
>
> Apologies if I'm misunderstanding what you're trying to do.
>
> --
> / Peter Schuller
>

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