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

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

On Tue, Jul 31, 2012 at 5:19 AM, Vladimir Stavrinov
<vst...@gm...> wrote:
> On Tue, Jul 31, 2012 at 05:35:45PM +0900, Michael Paquier wrote:
>
>>    The main problem that I see here is that replicating data
>>    asynchronously breaks MVCC.
>
> May I cite myself?
>
>         When read request come in, it should go to replicated node if and only if
>         requested data exists there, otherwise such request should go to distributed
>         node where those data in question exists in any case.
>
>>    So you are never sure that the data will be here or not on your
>>    background nodes.
>
> If we control where the data stored in distributed nodes, why not to control
> the state of replicated nodes? In both cases we should know what data is where.
>

If a data node has one or more sync rep standbys, it should be
theoretically possible to read balance those if that intelligence is
added to the coordinator. It would not matter if that data is in a
"distributed" or "replicated" table.

If it were asynchronous, there would be more tracking that would have
to be done to know if it is safe to load balance.

In some tests we have done at StormDB, the extra overhead for sync rep
is small, so you might as well use sync rep. With multiple replicas,
in sync rep mode it will continue working even there is a failure with
one of the replicas.


>>    Ideas are of course always welcome, but if you want to add some new
>>    features you will need to be more specific.
>
> I don't think what we discussing here is simply feature that may be added
> with an patch. The idea to move storage control on cluster level touches
> the basics and concept of XC.

Yeah, that is sounding different than what is done here. I am not sure
I understand what your requirements are and what exactly it is you
need.  If it is about HA, there are a lot of basics in place to build
out HA from that will probably meet your needs.

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

StormDB - http://www.stormdb.com
The Database Cloud