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

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

Performance numbers are necessary to prove the viability of this feature.
Some simple tests like with a table with millions of rows would be enough.

On Mon, Nov 26, 2012 at 8:42 PM, Ashutosh Bapat <
ash...@en...> wrote:

> Hi All,
> PFA patch which enables pushing down the ORDER BY clause or sorting to the
> Datanode/s through standard_planner().
>
> This patch leverages the already existing merge sort mechanism for
> RemoteQuery but now outside RemoteQuery using Sort plans.
>
> For a Sort plan it checks if all the expressions on which the result needs
> to be sorted are shippable and that the underlying tree allows to push
> ORDER BY to the Datanodes. If so, it includes the ORDER BY clause in the
> query to be sent to the Datanodes. If the number of Datanodes which
> participate in RemoteQuery is not 1, it adds a covering Sort node to merge
> the results from the Datanodes, otherwise, there is no covering Sort plan.
>
> The merge sort mechanism treats every Datanode as a tape and prefetches
> the results from the Datanode corresponding to a dwindling tape. This is
> enabled by setting the node from where to pull the next row before calling
> ExecProcNode on RemoteQueryState.
>
> The same mechanism is being used for Sort plan node under Group or Agg
> nodes.
>
> The patch adds test xc_sort.sql for testing this functionality. It also
> removes the now useless members sort and tuplesortstate from RemoteQuery
> and RemoteQueryState resp.
>



-- 
Michael Paquier
http://michael.otacoo.com