Re: [Postgres-xc-developers] Pushing down ORDER BY clauses or Sorting

On Fri, May 24, 2013 at 1:30 AM, Ashutosh Bapat <
ash...@en...> wrote:

> Hi All,
> While I hear Robert's presentation on query planning go wrong, I heard
> (first time) about MergeAppend plan. It looks like, we have something
> better to do with the way we are pushing the ORDER BY clauses and doing
> merge at the coordinator. Right now we are using Sort node and in ExecSort
> we start merging the rows. Instead, I think we should be using MergeAppend
> node.
>
>
I generally like this idea (though I saw below you did not get performance
numbers as expected). If we do this, it would also make sense to rework
RemoteQuery to use Append nodes for combining unsorted results from the
datanodes. But we will need some kind of parallelism at that node level so
that queries can be started and executed on all the child nodes at the same
time. AFAIK the current Append node executes serially i.e. it will move to
the next node only after finishing one subplan.

Thanks,
Pavan

-- 
Pavan Deolasee
http://www.linkedin.com/in/pavandeolasee