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

[Michael P. <mic...@gm...>]

On Sat, Oct 5, 2013 at 11:14 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.
Hum?! Logically, I would imagine that if A and T are distributed by x
this WHERE clause should be pushed down as the SET clause is a
constant. However perhaps UPDATE FROM does not have an explicit
support... Could you provide the version number and an EXPLAIN VERBOSE
output?

What if you put the where join in a subquery or a WITH clause? Like
that for example:
update T set T.a = -1 where A.x = (select A.x from A,T where A.x = T.x);
-- 
Michael