Re: Unable to execute Query in parallel for partitioned table

Hi Albe,

Thank you so much for information, will check this and get back to you if
any help required.

I have a doubt why didn't the parallelism works here ,could u plz guide me?

Thank you so much again.

On Thu, 11 Feb, 2021, 1:23 PM Laurenz Albe, <laurenz(dot)albe(at)cybertec(dot)at>
wrote:

> On Thu, 2021-02-11 at 05:09 +0530, Brajendra Pratap wrote:
> > I am unable to execute the below in parallel plz suggest how can I
> achieve parallelism here.
> >
> > select count(*) over () VIEWALLROWCOUNT,abc.*,ROW_NUMBER() OVER (order
> by trn_transaction_date desc ) AS RowNumber from (
> > select * from transactions where trn_store_date_id=20201202) abc;
> >
> > Query plan is as mentioned below :-
> >
> > explain analyze select count(*) over ()
> VIEWALLROWCOUNT,abc.*,ROW_NUMBER() OVER (order by trn_transaction_date
> desc ) AS RowNumber from (
> > select * from transactions where trn_store_date_id=20201218) abc;
> > LOG: duration: 25820.176 ms statement: explain analyze select count(*)
> over () VIEWALLROWCOUNT,abc.*,ROW_NUMBER() OVER (order by
> trn_transaction_date desc ) AS RowNumber from (
> > select * from transactions where trn_store_date_id=20201218) abc;
> >
> QUERY PLAN
> >
> ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
> > WindowAgg (cost=4474843.51..4498066.81 rows=774110 width=21297)
> (actual time=21455.495..25241.738 rows=795190 loops=1)
> > -> WindowAgg (cost=4474843.51..4488390.44 rows=774110 width=21289)
> (actual time=10588.494..15311.865 rows=795190 loops=1)
> > -> Sort (cost=4474843.51..4476778.79 rows=774110 width=21281)
> (actual time=10588.422..11771.300 rows=795190 loops=1)
> > Sort Key: transactions.trn_transaction_date DESC
> > Sort Method: external merge Disk: 1496856kB
> > -> Result (cost=0.00..270640.32 rows=774110
> width=21281) (actual time=0.117..4504.159 rows=795190 loops=1)
> > -> Append (cost=0.00..262899.22 rows=774110
> width=21281) (actual time=0.094..1449.532 rows=795190 loops=1)
> > -> Seq Scan on transactions
> (cost=0.00..0.00 rows=1 width=47554) (actual time=0.019..0.019 rows=0
> loops=1)
> > Filter: (trn_store_date_id = 20201218)
> > -> Index Scan using
> idx_202012_trn_store_date_id on transactions_202012 (cost=0.56..259028.67
> rows=774109 width=21281) (actual time=0.074..1357.764 rows=795190 loops=1)
> > Index Cond: (trn_store_date_id =
> 20201218)
> > Planning Time: 116.472 ms
> > Execution Time: 25676.098 ms
> >
> > Note :- We had tried different options like max_worker_processes,
> max_parallel_workers,
> max_parallel_workers_per_gather,max_parallel_maintenance_worker to execute
> it in parallel but no luck.
>
> I don't think parallelization will help you here.
>
> Your problem is probably the "abc.*" in the SELECT list.
>
> There must be really large data in this table, so it takes a long time to
> fetch and
> sort the rows. Try selecting only the columns you need.
>
> Alternatively, add a LIMIT clause. Do you really need all 800000 rows?
>
> Yours,
> Laurenz Albe
> --
> Cybertec | https://www.cybertec-postgresql.com
>
>