Re: [Postgres-xc-general] ERROR: Failed to get pooled connections

[Mason S. <ma...@st...>]

On Tue, Jul 31, 2012 at 8:25 AM, Vladimir Stavrinov
<vst...@gm...> wrote:
> On Tue, Jul 31, 2012 at 08:11:21AM -0400, Mason Sharp wrote:
>
>> If a data node has one or more sync rep standbys, it should be
>> theoretically possible to read balance those if that intelligence is
>
> "sync rep" means no "write balance"
>

I think you misunderstood. Tables can be either distributed or
replicated across the database segments. Each segment in turn can be
have multiple synchronous replicas, similar to PostgreSQL's
synchronous replication.

So, for your large write-heavy tables, you should distribute amongst
multiple nodes, gaining write scalability.  The overhead and added
latency for having replicas of each database segment is relatively
small, so you need not think of that as preventing "write balance", as
you say.

For tables where you want read scalability, you would want to
replicate those. This is at the table level, not the database segment
level. The coordinator will read balance those today.

If you also want read-balancing for distributed (non-replicated)
tables across the database segment replicas, that has not yet been
implemented, but is definitely doable (if your company would like to
sponsor such a change, we are happy to implement it). Supporting such
a change would involve changing the coordinator code to be able to
know about database segment replicas. Up until now the project has
focused on the challenges of the core database and not so much dealing
with stuff on the outside of it, like HA.

I hope that helps.

Regards,

Mason



> --
>
> ***************************
> ##  Vladimir Stavrinov
> ##  vst...@gm...
> ***************************
>



-- 
Mason Sharp

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