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Re: Evolving the client protocol


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On Wed, Apr 18, 2018 at 3:47 AM, Avi Kivity <avi@xxxxxxxxxxxx> wrote:

> Hello Cassandra developers,
>
>
> We're starting to see client protocol limitations impact performance, and
> so we'd like to evolve the protocol to remove the limitations. In order to
> avoid fragmenting the driver ecosystem and reduce work duplication for
> driver authors, we'd like to avoid forking the protocol. Since these issues
> affect Cassandra, either now or in the future, I'd like to cooperate on
> protocol development.
>
>
> Some issues that we'd like to work on near-term are:
>
>
> 1. Token-aware range queries
>
>
> When the server returns a page in a range query, it will also return a
> token to continue on. In case that token is on a different node, the client
> selects a new coordinator based on the token. This eliminates a network hop
> for range queries.
>
>
> For the first page, the PREPARE message returns information allowing the
> client to compute where the first page is held, given the query parameters.
> This is just information identifying how to compute the token, given the
> query parameters (non-range queries already do this).
>
>
> https://issues.apache.org/jira/browse/CASSANDRA-14311
>
>
> 2. Per-request timeouts
>
>
> Allow each request to have its own timeout. This allows the user to set
> short timeouts on business-critical queries that are invalid if not served
> within a short time, long timeouts for scanning or indexed queries, and
> even longer timeouts for administrative tasks like TRUNCATE and DROP.
>
>
> https://issues.apache.org/jira/browse/CASSANDRA-2848
>
>
> 3. Shard-aware driver
>
>
> This admittedly is a burning issue for ScyllaDB, but not so much for
> Cassandra at this time.
>
>
> In the same way that drivers are token-aware, they can be shard-aware -
> know how many shards each node has, and the sharding algorithm. They can
> then open a connection per shard and send cql requests directly to the
> shard that will serve them, instead of requiring cross-core communication
> to happen on the server.
>
>
> https://issues.apache.org/jira/browse/CASSANDRA-10989
>
>
> I see three possible modes of cooperation:
>
>
> 1. The protocol change is developed using the Cassandra process in a JIRA
> ticket, culminating in a patch to doc/native_protocol*.spec when consensus
> is achieved.
>
>
> The advantage to this mode is that Cassandra developers can verify that
> the change is easily implementable; when they are ready to implement the
> feature, drivers that were already adapted to support it will just work.
>
>
> 2. The protocol change is developed outside the Cassandra process.
>
>
> In this mode, we develop the change in a forked version of
> native_protocol*.spec; Cassandra can still retroactively merge that change
> when (and if) it is implemented, but the ability to influence the change
> during development is reduced.
>
>
> If we agree on this, I'd like to allocate a prefix for feature names in
> the SUPPORTED message for our use.
>
>
> 3. No cooperation.
>
>
> This requires the least amount of effort from Cassandra developers (just
> enough to reach this point in this email), but will cause duplication of
> effort for driver authors who wish to support both projects, and may cause
> Cassandra developers to redo work that we already did.
>
>
> Looking forward to your views.
>
>
> Avi
>
>
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