QUERY spending lot of time in operator "ParallelUnion"
I have a complex query with 2 inner joins and 5 LEFT outer joins on multiple dimension tables.
Fact table size : 70 million rows.
- I created a view with the query.
- The projections are all pretty good to operate.
- Explain plan appears ok.
Environment : Vertica Analytic Database v7.1.2-0
When I execute the query with a limit 10k rows, the output is generated in 15 seconds. But when I attempt CTAS task (create table as select * from view) , it runs forever.
When I look in to execution_engine_profiles it reports highest clock time spent on operator "ParallelUnion". The strange issue is that normal select delivers data as expected but the same does not work on CTAS task.
Let me know if anyone can shed some light on this operator.