[Postgres-xl-developers] Coordinator with Datanode

Mason S masonlists at gmail.com
Wed Mar 11 16:50:15 PDT 2015


On Tue, Mar 10, 2015 at 12:59 AM, Ramanuj Hari <hari.ramanuj at gmail.com>
wrote:

> Hi Experts,
>
> I am facing an issue while taking decision. Not able to correctly arrive
> conclusion.
>
>
> What is the correct way to deploy Postgres-XL.
>
> [1] One VM to have Coordinator and Datanode.
>
[2] Based on connection requirement and database size requirement, we can
> decide how many Coordinator and Datanode is needed, and deploy Coordinator
> and Datanode on seperate VM.
>
>
> What I am not able to figure out what's wrong with 1st option, because I
> never saw any deployment of 1st type discussed in any of the mailing
> thread.
>
>
There are additional options. For example, with multiple vCPUs, you can
have multiple Datanodes per VM.

In general, yes, I would likely colocate a Coordinator and Datanode,
especially with high concurrency. If you have low concurrency, you may not
necessarily bother with a Coordinator on every VM. If it is a for a low
concurrency BI workload with a heavy workload for individual queries, you
could break the Coordinator out onto a separate smaller VM.



> 1st option looks simple enough, but will it fit for infinite scaling
> model, where to increase number of connection/ DB size, we can just spin
> off a new VM (having coordinator and Datanode) and add the same to running
> Postgres-XL cluster.
>

While you can add nodes to XL, it does not automatically redistribute data,
you will have to do that as a separate step. So, instead you may wish to
move off Datanodes to their own VMs as you grow, as a first step.


>
> What is the overhead of running very high number of Coordinator(say 100 or
> so), even though that many number of coordinator is not exactly required.
>
>
I do not know anyone who has tried 100 Coordinators, but the Coordinators
really only communicate with one another for DDL, so most activity will
just be fulfilling user requests.


Regards,

Mason
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