Re: [Postgres-xc-general] modifying values at the datanode

[Sandeep G. <gup...@gm...>]

Hi Ashutosh,

 Thanks for the note.  I cannot commit right away. However, whenever you
have some time can you mention relevant portions in the codebase where
changes have to be made. I have a general understanding of the execution
engine. I will take a look see if it feasible for me.

Thanks.
Sandeep



On Sun, Oct 6, 2013 at 11:53 PM, Ashutosh Bapat <
ash...@en...> wrote:

>
>
>
> On Sat, Oct 5, 2013 at 7:44 PM, Sandeep Gupta <gup...@gm...>wrote:
>
>> Thanks Michael. I understand. The only issue is that we have an update
>> query as
>>
>> update T set T.a = -1 from A where A.x = T.x
>>
>>
>> Both A and T and distributed by x column. The problem is that coordinator
>> first does the join and then
>> calls update several times at each datanode. This is turning out to be
>> too slow. Would have
>> been better if the entire query was shipped to the datanodes.
>>
>>
> Right now there is no way to ship a DML with more than one relation
> involved there. But that's something, I have been thinking about. If you
> have developer resources and can produce a patch. I can help.
>
>
>> Thanks.
>> Sandeep
>>
>>
>>
>> On Sat, Oct 5, 2013 at 6:27 AM, Michael Paquier <
>> mic...@gm...> wrote:
>>
>>> On Sat, Oct 5, 2013 at 2:58 AM, Sandeep Gupta <gup...@gm...>
>>> wrote:
>>> >  I understand that the datanodes are read only and that updates/insert
>>> can
>>> > happen at coordinator.
>>> You got it.
>>>
>>> > Also, it does not allow modification of column over which the records
>>> are distributed.
>>> Hum no, 1.1 allows ALTER TABLE that you can use to change the
>>> distribution type of a table.
>>>
>>> > However, in case I know what I am doing, it there anyway possible to
>>> modify
>>> > the values directly at datanodes.
>>> > The modifications are not over column over which distribution happens.
>>> If you mean by connecting directly to the Datanodes, no. You would
>>> break data consistency if table is replicated by the way by doing
>>> that. Let the Coordinator planner do the job and choose the remote
>>> nodes for you.
>>>
>>> There have been discussion to merge Coordinators and Datanodes
>>> together though. This would allow what you say, with a simpler cluster
>>> design.
>>> --
>>> Michael
>>>
>>
>>
>>
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>
>
> --
> Best Wishes,
> Ashutosh Bapat
> EnterpriseDB Corporation
> The Postgres Database Company
>