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Subject: Re: cost estimate about some Cassandra patchs
From: aaron morton <aaron@thelastpickle.com>
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Date: Tue, 7 May 2013 20:21:47 +1200
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References: 
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To: user@cassandra.apache.org

> Use case =3D rows with rowkey like (folder id, file id)
> And operations read/write multiple rows with same folder id =3D> so, =
it could make sense to have a partitioner putting rows with same "folder =
id" on the same replicas.
The entire row key the thing we use to make the token used to both =
locate the replicas and place the row in the node. I don't see that =
changing.=20

Have you done any performance testing to see if this is a problem?

Cheers
=20
-----------------
Aaron Morton
Freelance Cassandra Consultant
New Zealand

@aaronmorton
http://www.thelastpickle.com

On 7/05/2013, at 5:27 AM, DE VITO Dominique =
<dominique.devito@thalesgroup.com> wrote:

> > De : aaron morton [mailto:aaron@thelastpickle.com]=20
> > Envoy=E9 : dimanche 28 avril 2013 22:54
> > =C0 : user@cassandra.apache.org
> > Objet : Re: cost estimate about some Cassandra patchs
> >=20
> > > Does anyone know enough of the inner working of Cassandra to tell =
me how much work is needed to patch Cassandra to enable such =
communication vectorization/batch ?
> >=20
> =20
> > Assuming you mean "have the coordinator send multiple row read/write =
requests in a single message to replicas"
> >=20
> > Pretty sure this has been raised as a ticket before but I cannot =
find one now.=20
> >=20
> > It would be a significant change and I'm not sure how big the =
benefit is. To send the messages the coordinator places them in a queue, =
there is little delay sending. Then it waits on them async. So there may =
be some saving on networking but from the coordinators point of view I =
think the impact is minimal.=20
> >=20
> > What is your use case?
> =20
> Use case =3D rows with rowkey like (folder id, file id)
> And operations read/write multiple rows with same folder id =3D> so, =
it could make sense to have a partitioner putting rows with same "folder =
id" on the same replicas.
> =20
> But so far, Cassandra is not able to exploit this locality as batch =
effect ends at the coordinator node.
> =20
> So, my question about the cost estimate for patching Cassandra.
> =20
> The closest (or exactly corresponding to my need ?) JIRA entries I =
have found so far are:
> =20
> CASSANDRA-166: Support batch inserts for more than one key at once
> https://issues.apache.org/jira/browse/CASSANDRA-166
> =3D> "WON'T FIX" status
> =20
> CASSANDRA-5034: Refactor to introduce Mutation Container in write path
> https://issues.apache.org/jira/browse/CASSANDRA-5034
> =3D> I am not very sure if it's related to my topic
> =20
> Thanks.
> =20
> Dominique
> =20
> =20
> =20
> >=20
> > Cheers
> >=20
> >=20
> > -----------------
> > Aaron Morton
> > Freelance Cassandra Consultant
> > New Zealand
> >=20
> > @aaronmorton
> > http://www.thelastpickle.com
> =20
> On 27/04/2013, at 4:04 AM, DE VITO Dominique =
<dominique.devito@thalesgroup.com> wrote:
>=20
>=20
> Hi,
> =20
> We are created a new partitioner that groups some rows with =
**different** row keys on the same replicas.
> =20
> But neither the batch_mutate, or the multiget_slice are able to take =
opportunity of this partitioner-defined placement to vectorize/batch =
communications between the coordinator and the replicas.
> =20
> Does anyone know enough of the inner working of Cassandra to tell me =
how much work is needed to patch Cassandra to enable such communication =
vectorization/batch ?
> =20
> Thanks.
> =20
> Regards,
> Dominique
> =20
> =20