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
