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From Robert Coli <rc...@eventbrite.com>
Subject Re: CQL flow control
Date Wed, 05 Feb 2014 18:55:48 GMT
On Wed, Feb 5, 2014 at 6:14 AM, Ben Hood <0x6e6562@gmail.com> wrote:

> What is the general approach to this from a server perspective? Is
> there any flow control that the server can apply to back pressure onto
> the sending driver?


No. In theory the client could look at dynamic snitch scores, I suppose, if
the dynamic snitch worked right...

For most clients, my belief is the only backpressure is that, once a node
is severely overloaded, it will stop attempting to write hints and return
an OverloadedException. But this is only on the hint write path, not the
normal write path.


> If not, how do other driver implementors view this situation? Do you
> try to maintain some kind of flow control at the driver level so that
> you can push back onto the app, or you just let the effects of IO
> saturation just bubble up to the app?
>

I think most deploys of Cassandra deal with this reality by carefully
managing available capacity so that they don't risk getting in this
situation.

I understand that is not a technical solution appropriate to your
question's scope, but I do believe it describes the status quo.

=Rob

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