Re: [Postgres-xc-general] pushing order by clause to datanodes

How about a plan where the datanodes perform the sort as well and the
coordinator performs a sorted merge?

Are such plans not part of the query planner?

-Sandeep

On 10/17/2013 07:04 AM, Ashutosh Bapat wrote:
> There is GROUP BY clause that needs to be evaluated before the result 
> can be ordered. Thus GROUP BY is sent to the datanode but not ORDER BY.
>
>
> On Thu, Oct 17, 2013 at 4:31 PM, Sandeep Gupta 
> <gup...@gm... <mailto:gup...@gm...>> wrote:
>
>     Hi Ashutosh,
>
>
>       Attached below is the query and the corresponding query plan. I
>     am using version 1.1.
>     Thanks for taking a look at this.
>
>     -Sandeep
>
>     SELECT exposed_time effectedDate, ROUND(COUNT(a.pid)/10) COUNT FROM public.vt_demography_info_xc d, public.ses_vt_20130805_xc a WHERE d.pid=a.pid AND d.countyid='50015' AND d.age BETWEEN 5 AND 18 AND d.gender=1 GROUP BY exposed_time ORDER BY exposed_time;
>
>
>
>
>                                         QUERY PLAN (Coordinator)
>
>       Sort  (cost=10000000005.03..10000000005.03 rows=1 width=8)
>         Output: a.exposed_time, (round(((count((count(a.pid))) / 10))::double precision))
>         Sort Key: a.exposed_time
>         ->  HashAggregate  (cost=5.00..5.02 rows=1 width=8)
>               Output: a.exposed_time, round(((count((count(a.pid))) / 10))::double precision)
>               ->  Data Node Scan on "__REMOTE_GROUP_QUERY__"  (cost=0.00..0.00 rows=1000 width=8)
>                     Output: a.exposed_time, (count(a.pid))
>                     Node/s: datanode1, datanode10, datanode11, datanode12, datanode13, datanode14, datanode15, datanode16, datanode2, datanode3, datanode4, datanode5, datanode6, datanode7, datanode8, datanode9
>                     Remote query: SELECT r.a_1, count(r.a_2) FROM ((SELECT d.pid FROM ONLY public.vt_demography_info_xc d WHERE ((d.age >= 5) AND (d.age <= 18) AND ((d.countyid)::text = '50015'::text) AND (d.gender = 1))) l(a_1) JOIN (SELECT a.exposed_time, a.pid FROM ONLY public.ses_vt_20130805_xc a WHERE ((a.exposed_time >= 4667) AND (a.exposed_time <= 5031))) r(a_1, a_2) ON (true)) WHERE (l.a_1 = r.a_2) GROUP BY 1
>     (9 rows)
>
>                                           QUERY PLAN (Datanode)
>
>       GroupAggregate  (cost=0.00..47862.29 rows=225 width=8)
>         Output: a.exposed_time, round(((count(a.pid) / 10))::double precision)
>         ->  Nested Loop  (cost=0.00..47856.05 rows=460 width=8)
>               Output: a.exposed_time, a.pid
>               ->  Index Scan using et_ses on public.ses_vt_20130805_xc a  (cost=0.00..7283.10 rows=129583 width=8)
>                     Output: a.pid, a.rep, a.exposed_time, a.infectious_time, a.recovered_time
>                     Index Cond: ((a.exposed_time >= 4667) AND (a.exposed_time <= 5031))
>               ->  Index Scan using pid_demo on public.vt_demography_info_xc d  (cost=0.00..0.30 rows=1 width=4)
>                     Output: d.pid, d.hid, d.age, d.gender, d.zipode, d.blockgroupid, d.longitude, d.lattitude, d.county, d.countyid
>                     Index Cond: (d.pid = a.pid)
>                     Filter: ((d.age >= 5) AND (d.age <= 18) AND ((d.countyid)::text = '50015'::text) AND (d.gender = 1))
>     (11 rows)
>
>
>
>
>     On Thu, Oct 17, 2013 at 12:12 AM, Ashutosh Bapat
>     <ash...@en...
>     <mailto:ash...@en...>> wrote:
>
>         Sandeep,
>         It would be nice if you mention the version of XC in your
>         mail. Sort push down is available from 1.1 onwards. If you do
>         not see sort getting pushed down in 1.1, please report
>         detailed definitions of the tables, query and the EXPLAIN output.
>
>
>         On Thu, Oct 17, 2013 at 1:09 AM, Sandeep Gupta
>         <gup...@gm... <mailto:gup...@gm...>> wrote:
>
>             Hi,
>
>              In an another query that requires the result to be
>             aggregated and ordered by a field (lets say timeo)
>             the query planner currently pulls the results and then
>             performs a sort with hash aggregate.
>
>             The table at the datanodes are clustered by timeo. I was
>             wondering if it possible
>             for query planner to push down the order by clause at the
>             datanode and then perform
>             sort-merge aggregate at the coordinator. Surely, that
>             would be a better query plan.
>
>             We have tried enable_sort=off etc. but that doesn't work.
>
>             Thanks.
>             Sandeep
>
>
>
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>
>         -- 
>         Best Wishes,
>         Ashutosh Bapat
>         EnterpriseDB Corporation
>         The Postgres Database Company
>
>
>
>
>
> -- 
> Best Wishes,
> Ashutosh Bapat
> EnterpriseDB Corporation
> The Postgres Database Company