Re: Parallel Aggregate

I've done some testing with one of my data sets in an 8VPU virtual environment and this is looking really, really good.

My test query is:

SELECT pageview, sum(pageview_count)

FROM fact_agg_2015_12

GROUP BY date_trunc('DAY'::text, pageview);

The query returns 15 rows. The fact_agg table is 5398MB and holds around 25 million records.

Explain with a max_parallel_degree of 8 tells me that the query will only use 6 background workers. I have no indexes on the table currently.

Finalize HashAggregate  (cost=810142.42..810882.62 rows=59216 width=16)

   Group Key: (date_trunc('DAY'::text, pageview))

   ->  Gather  (cost=765878.46..808069.86 rows=414512 width=16)

         Number of Workers: 6

         ->  Partial HashAggregate  (cost=764878.46..765618.66 rows=59216 width=16)

               Group Key: date_trunc('DAY'::text, pageview)

               ->  Parallel Seq Scan on fact_agg_2015_12  (cost=0.00..743769.76 rows=4221741 width=12)