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Re: Evolving the client protocol


Port-per-shard is likely the easiest option but it's too ugly to contemplate. We run on machines with 160 shards (IBM POWER 2s20c160t IIRC), it will be just horrible to have 160 open ports.


It also doesn't fit will with the NICs ability to automatically distribute packets among cores using multiple queues, so the kernel would have to shuffle those packets around. Much better to have those packets delivered directly to the core that will service them.


(also, some protocol changes are needed so the driver knows how tokens are distributed among shards)

On 2018-04-19 19:46, Ben Bromhead wrote:
WRT to #3
To fit in the existing protocol, could you have each shard listen on a
different port? Drivers are likely going to support this due to
https://issues.apache.org/jira/browse/CASSANDRA-7544 (
https://issues.apache.org/jira/browse/CASSANDRA-11596).  I'm not super
familiar with the ticket so their might be something I'm missing but it
sounds like a potential approach.

This would give you a path forward at least for the short term.


On Thu, Apr 19, 2018 at 12:10 PM Ariel Weisberg <ariel@xxxxxxxxxxx> wrote:

Hi,

I think that updating the protocol spec to Cassandra puts the onus on the
party changing the protocol specification to have an implementation of the
spec in Cassandra as well as the Java and Python driver (those are both
used in the Cassandra repo). Until it's implemented in Cassandra we haven't
fully evaluated the specification change. There is no substitute for trying
to make it work.

There are also realities to consider as to what the maintainers of the
drivers are willing to commit.

RE #1,

I am +1 on the fact that we shouldn't require an extra hop for range scans.

In JIRA Jeremiah made the point that you can still do this from the client
by breaking up the token ranges, but it's a leaky abstraction to have a
paging interface that isn't a vanilla ResultSet interface. Serial vs.
parallel is kind of orthogonal as the driver can do either.

I agree it looks like the current specification doesn't make what should
be simple as simple as it could be for driver implementers.

RE #2,

+1 on this change assuming an implementation in Cassandra and the Java and
Python drivers.

RE #3,

It's hard to be +1 on this because we don't benefit by boxing ourselves in
by defining a spec we haven't implemented, tested, and decided we are
satisfied with. Having it in ScyllaDB de-risks it to a certain extent, but
what if Cassandra decides to go a different direction in some way?

I don't think there is much discussion to be had without an example of the
the changes to the CQL specification to look at, but even then if it looks
risky I am not likely to be in favor of it.

Regards,
Ariel

On Thu, Apr 19, 2018, at 9:33 AM, glommer@xxxxxxxxxxxx wrote:

On 2018/04/19 07:19:27, kurt greaves <kurt@xxxxxxxxxxxxxxx> wrote:
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.
I don't think forking would be desirable (for anyone) so this seems
the most reasonable to me. For 1 and 2 it certainly makes sense but
can't say I know enough about sharding to comment on 3 - seems to me
like it could be locking in a design before anyone truly knows what
sharding in C* looks like. But hopefully I'm wrong and there are
devs out there that have already thought that through.
Thanks. That is our view and is great to hear.

About our proposal number 3: In my view, good protocol designs are
future proof and flexible. We certainly don't want to propose a design
that works just for Scylla, but would support reasonable
implementations regardless of how they may look like.

Do we have driver authors who wish to support both projects?

Surely, but I imagine it would be a minority. ​

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Ben Bromhead
CTO | Instaclustr <https://www.instaclustr.com/>
+1 650 284 9692
Reliability at Scale
Cassandra, Spark, Elasticsearch on AWS, Azure, GCP and Softlayer



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