union all taking years - PG 9.6

[Patrick B <patrickbakerbr@xxxxxxxxx>]

Hi guys.

I have two tables, where 'tableA' is the old and 'tableC' is the new one. I say "new/old" because we are migrating the data from tableA to tableC soon.

I created a view selecting from both tables, with a UNION ALL between them. When selecting from that view, it's really slow. I can't even run explain analyze (it's been 1h and query did not finished yet).

However, when running both selects with explain analyze, query is fast.

What should I do in this case? Why is that taking so long? I assume it's because the UNION will look for duplicates?

Thanks

Patrick.