On 2 June 2018 at 22:46, Ashutosh Bapat <ashutosh.bapat@enterprisedb.com> wrote:
>>>> And that is why both XL and "FDW approach" rely on a central coordinator.
>>>
>>> I don't think we ever specified that "FDW approach" "relies" on a
>>> central coordinator. One could configure and setup a cluster with
>>> multiple coordinators using FDWs.
>>
>> Yes, of course. You're just misunderstanding me. I'm talking about a
>> query coordinator "role". There can be many coordinator components and
>> they can be spread out in variours ways, but for any one SQL query
>> there needs to be one coordinator node. Not a SPOF.
>
> In your earlier mail, which is included above, you mentioned central
> coordinator for multi-node transaction control and global deadlock
> detection. That doesn't sound like a "query coordinator role". It
> sounds more like GTM, which is an SPOF.
In XL, GTM is a singe component managing transaction ids. That has a
standby, so is not a SPOF.
But that is not what I mean. I don't believe that a GTM-style
component is necessary in a future in-core scalablility solution.
Each incoming query needs to be planned and executed from one
coordinator component, then the work performed across many workers on
different nodes (or just one). We could have coordinator components on
each worker node, or we could have a set of coordinator nodes and a
set of worker nodes.
--
Simon Riggs http://www.2ndQuadrant.com/
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